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saymrwulf
09fe47c59d
sub_val_spec closes the top-level two-clause value spec: denote(Scalar52.sub a b) = denote(a) - denote(b) in ZMod l for limb-bounded inputs with canonical subtrahend (scVal b < l). Axiom-clean [propext, Classical.choice, Quot.sound]; no sorry. The assembly documented-as-remaining last session is now done. Key resolutions: - Applied the WP "spec_bind" rule manually instead of "step", and reduced the resulting "let (difference,borrow) := (dw,w)" Prod-let with an explicit "show" — this was the destructuring friction that blocked the earlier attempt (step's arity heuristics mis-typed the pair result). - Inlined the subtle "Choice::from" identity (no step-spec, like csel_step). - PERFORMANCE: kept "scLimbs" as opaque atoms in the gamma5=1 derivation instead of "unfold ... at *" — the unfold exploded omega with 2^52..2^260 coefficients and blew past 600s; atomic form proves in ~1 min (METHOD 4, same kernel-cost discipline as the field layer). - The 2^260 borrow-wrap and the +l conditional-add cancel in ZMod l: beta5=0 direct; beta5=1 forces top carry gamma5=1 from scVal b < l, closed by linear_combination over the two telescopes (sub_telescope, add_telescope). check-scalar.sh: sub_val_spec in the manifest + Phase-3 audit (4/4 clean); proof-phase caps raised to 600s/8192MB for the assembly; full button green. exponentiation.threshold raised to 300 for the 2^260 literal. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
816 lines
38 KiB
Text
816 lines
38 KiB
Text
/- ──────────────────────────────────────────────────────────────────────────────
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Proofs/ScalarSubSpec.lean — Scalar52 subtraction mod ℓ (value + bounds)
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WHAT THIS FILE CONTAINS
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The full two-clause spec for the transpiled `Scalar52::sub`:
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given limb-bounded inputs, `sub a b` never panics and returns s with
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scVal s = scVal a - scVal b (if scVal b ≤ scVal a)
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scVal s = scVal a + ℓ - scVal b (if scVal a < scVal b)
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— no hypotheses beyond ScBnd are needed: in the borrow branch the result
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is automatically < ℓ, and in the no-borrow branch it is exactly the
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ℕ-difference (callers derive canonicity per use-site; see scalar_sub_spec
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below and ScalarAddSpec.lean).
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RUST ANALOG (curve25519-dalek v5, src/backend/serial/u64/scalar.rs:177-191)
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let mut difference = Scalar52::ZERO; let mask = (1u64 << 52) - 1;
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let mut borrow: u64 = 0;
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for i in 0..5 {
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borrow = a[i].wrapping_sub(b[i] + (borrow >> 63));
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difference[i] = borrow & mask;
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}
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let underflow = Choice::from((borrow >> 63) as u8);
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difference.conditional_add_l(underflow); // + ℓ iff underflow
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Transpiled: `Scalar52.sub` → `sub_loop` (5 iterations) →
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`conditional_add_l` → `conditional_add_l_loop` (5 iterations), in
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gen/CurveScalar/Funs.lean. The `subtle` Choice/conditional_select are
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faithful models in gen/CurveScalar/FunsExternal.lean (documented there).
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PROOF ARCHITECTURE (the post-OOM discipline, cf. control repo METHOD 4)
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1. `nat_and_mask52` / `nat_shift52` / `nat_shift63` — bit ops → %,/ .
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2. `sub_step_arith` — ONE limb's borrow accounting, an isolated ℕ lemma
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with a tiny context: d + b + β_in = a + 2^52·β_out, β ∈ {0,1}.
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3. `sub_loop_spec` — 5-fold unroll via loop_step/range_next_*_spec
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(infrastructure from Proofs/ScalarLoop.lean), producing the five
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per-limb equations and the borrow bit.
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4. `cond_add_l_spec` — 5-fold unroll of the conditional add of L, per-limb
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carry accounting (γ chain), both Choice cases.
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5. Telescoping is done at the scVal level over ℤ with explicitly stated
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linear combinations (certificates checked, never searched — the
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kernel-capacity lesson from the pasta campaign).
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6. `sub_val_spec` (general) and `scalar_sub_spec` (canonical certificate).
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ROLE IN THE PYRAMID
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Second brick of the scalar layer (after ScalarDenote's L_val): with add
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(ScalarAddSpec.lean) it gives the group ℤ/ℓ its verified + and −.
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────────────────────────────────────────────────────────────────────────────── -/
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import Proofs.ScalarDenote
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import Proofs.ScalarLoop
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import Mathlib.Tactic.LinearCombination
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open Aeneas Aeneas.Std Result
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open curve25519_dalek
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set_option maxHeartbeats 4000000
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set_option linter.unusedSimpArgs false
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set_option exponentiation.threshold 300
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namespace ScalarProofs
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open Aeneas.Std.WP
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/-! ### Bit-op ↔ arithmetic conversion (ℕ level)
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The scalar code uses the 52-bit mask and shifts by 52 / 63; convert them to
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`%` / `/` so `omega` can reason. Same pattern as the field layer's
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`nat_and_mask` / `nat_shift_div` (Proofs/ReduceSpec.lean), at the scalar
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radix. 4503599627370495 = 2^52 − 1, 4503599627370496 = 2^52. -/
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theorem nat_and_mask52 (n : ℕ) : n &&& (2^52 - 1) = n % 2^52 :=
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Nat.and_two_pow_sub_one_eq_mod n 52
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theorem nat_shift52 (n : ℕ) : n >>> 52 = n / 2^52 := by
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simp [Nat.shiftRight_eq_div_pow]
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theorem nat_shift63 (n : ℕ) : n >>> 63 = n / 2^63 := by
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simp [Nat.shiftRight_eq_div_pow]
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/-! ### The isolated per-limb borrow step (ℕ, tiny context) -/
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/-- One limb of the subtraction loop, as pure ℕ arithmetic.
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MATH: for a, b < 2^52 and borrow-in bit β ∈ {0,1}, let
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w = (a + 2^64 − (b + β)) % 2^64 (the wrapping_sub result)
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d = w % 2^52 (the stored limb, w &&& mask)
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β' = w / 2^63 (the borrow-out bit, w >>> 63)
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then β' ≤ 1 and d + b + β = a + 2^52 · β'.
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WHY THIS SHAPE: the identity is stated with the correction on the LEFT so
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it lives entirely in ℕ (no truncated subtraction anywhere) — the exact
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discipline the toy system's proof used (curriculum Interlude, I.4).
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The context is five small naturals; `omega` decides it without any
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2^260-scale coefficients entering a certificate. -/
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theorem sub_step_arith (a b β : ℕ) (ha : a < 2^52) (hb : b < 2^52) (hβ : β ≤ 1) :
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(a + 2^64 - (b + β)) % 2^64 / 2^63 ≤ 1 ∧
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(a + 2^64 - (b + β)) % 2^64 % 2^52 + b + β
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= a + 2^52 * ((a + 2^64 - (b + β)) % 2^64 / 2^63) := by
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constructor
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· omega
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· omega
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/-! ### ZERO's limbs -/
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/-- `Scalar52::ZERO` is five zero limbs. Rust: scalar.rs:62. -/
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theorem ZERO_limbs :
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(↑backend.serial.u64.scalar.Scalar52.ZERO : List U64) = [0#u64, 0#u64, 0#u64, 0#u64, 0#u64] := by
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unfold backend.serial.u64.scalar.Scalar52.ZERO
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rfl
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/-! ### The subtraction loop, unrolled 5-fold
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Same architecture as the field layer's `add_limbs_spec`
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(Proofs/AddSpec.lean): `loop_step` peels an iteration, `range_next_lt_spec`
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steps the iterator, `step` runs each body operation, and the 6th peel
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(`range_next_ge_spec`, 5 ≥ 5) exits. The postcondition carries the five
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per-limb borrow equations of `sub_step_arith` plus the final borrow bit. -/
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/-- Limb-level spec for `sub_loop` started in its actual initial state
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(range 0..5, difference = ZERO, borrow = 0), for 52-bit-bounded inputs.
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MATH: there exist limbs d0..d4 (< 2^52) and borrow bits β1..β5 ∈ {0,1}:
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d_i + b_i + β_i = a_i + 2^52·β_{i+1} (β_0 = 0)
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and the returned borrow word w has w >>> 63 = β5.
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Telescoping these five equations (done by the caller) gives
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scLimbs d + scVal b = scLimbs a + 2^260·β5. -/
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theorem sub_loop_spec (a b : Sc) (mask : U64)
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(a0 a1 a2 a3 a4 b0 b1 b2 b3 b4 : U64)
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(ha : (↑a : List U64) = [a0, a1, a2, a3, a4])
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(hb : (↑b : List U64) = [b0, b1, b2, b3, b4])
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(hmask : mask.val = 2^52 - 1)
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(hbnd : a0.val < 2^52 ∧ a1.val < 2^52 ∧ a2.val < 2^52 ∧ a3.val < 2^52 ∧ a4.val < 2^52 ∧
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b0.val < 2^52 ∧ b1.val < 2^52 ∧ b2.val < 2^52 ∧ b3.val < 2^52 ∧ b4.val < 2^52) :
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backend.serial.u64.scalar.Scalar52.sub_loop
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{ start := 0#usize, «end» := 5#usize } a b
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backend.serial.u64.scalar.Scalar52.ZERO mask 0#u64
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⦃ (dw : Sc × U64) => ∃ d0 d1 d2 d3 d4 : U64, ∃ β1 β2 β3 β4 β5 : ℕ,
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(↑dw.1 : List U64) = [d0, d1, d2, d3, d4] ∧
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β1 ≤ 1 ∧ β2 ≤ 1 ∧ β3 ≤ 1 ∧ β4 ≤ 1 ∧ β5 ≤ 1 ∧
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d0.val < 2^52 ∧ d1.val < 2^52 ∧ d2.val < 2^52 ∧ d3.val < 2^52 ∧ d4.val < 2^52 ∧
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d0.val + b0.val = a0.val + 2^52 * β1 ∧
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d1.val + b1.val + β1 = a1.val + 2^52 * β2 ∧
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d2.val + b2.val + β2 = a2.val + 2^52 * β3 ∧
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d3.val + b3.val + β3 = a3.val + 2^52 * β4 ∧
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d4.val + b4.val + β4 = a4.val + 2^52 * β5 ∧
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dw.2.val >>> 63 = β5 ⦄ := by
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obtain ⟨hA0, hA1, hA2, hA3, hA4, hB0, hB1, hB2, hB3, hB4⟩ := hbnd
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unfold backend.serial.u64.scalar.Scalar52.sub_loop
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-- Iteration 1 (i = 0, borrow-in = 0)
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apply loop_step
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simp only [backend.serial.u64.scalar.Scalar52.sub_loop.body,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut]
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step with range_next_lt_spec as ⟨o1, iter1, ho1, hs1, he1⟩
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simp only [ho1]
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step as ⟨x1, hx1⟩
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step as ⟨y1, hy1⟩
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simp [ha, hb] at hx1 hy1
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step as ⟨sh1, hsh1⟩
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step as ⟨t1, ht1⟩
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step as ⟨w1, hw1⟩
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step as ⟨p1, back1, hpe1, hbk1⟩
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step as ⟨m1, hm1⟩
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try simp only [spec_ok]
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-- Iteration 2 (i = 1)
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apply loop_step
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simp only [backend.serial.u64.scalar.Scalar52.sub_loop.body,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut]
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step with range_next_lt_spec as ⟨o2, iter2, ho2, hs2, he2⟩
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simp only [ho2]
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step as ⟨x2, hx2⟩
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step as ⟨y2, hy2⟩
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simp [ha, hb, hs1, he1] at hx2 hy2
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step as ⟨sh2, hsh2⟩
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have hsh2b : sh2.val ≤ 1 := by
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have h64 : w1.val < 2^64 := by scalar_tac
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rw [hsh2, nat_shift63]; omega
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have hy2b : y2.val < 2^52 := by simp only [hy2]; exact hB1
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step as ⟨t2, ht2⟩
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step as ⟨w2, hw2⟩
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step as ⟨p2, back2, hpe2, hbk2⟩
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step as ⟨m2, hm2⟩
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try simp only [spec_ok]
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-- Iteration 3 (i = 2)
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apply loop_step
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simp only [backend.serial.u64.scalar.Scalar52.sub_loop.body,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut]
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step with range_next_lt_spec as ⟨o3, iter3, ho3, hs3, he3⟩
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simp only [ho3]
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step as ⟨x3, hx3⟩
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step as ⟨y3, hy3⟩
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simp [ha, hb, hs1, he1, hs2, he2] at hx3 hy3
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step as ⟨sh3, hsh3⟩
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have hsh3b : sh3.val ≤ 1 := by
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have h64 : w2.val < 2^64 := by scalar_tac
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rw [hsh3, nat_shift63]; omega
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have hy3b : y3.val < 2^52 := by simp only [hy3]; exact hB2
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step as ⟨t3, ht3⟩
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step as ⟨w3, hw3⟩
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step as ⟨p3, back3, hpe3, hbk3⟩
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step as ⟨m3, hm3⟩
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try simp only [spec_ok]
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-- Iteration 4 (i = 3)
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apply loop_step
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simp only [backend.serial.u64.scalar.Scalar52.sub_loop.body,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut]
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step with range_next_lt_spec as ⟨o4, iter4, ho4, hs4, he4⟩
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simp only [ho4]
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step as ⟨x4, hx4⟩
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step as ⟨y4, hy4⟩
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simp [ha, hb, hs1, he1, hs2, he2, hs3, he3] at hx4 hy4
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step as ⟨sh4, hsh4⟩
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have hsh4b : sh4.val ≤ 1 := by
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have h64 : w3.val < 2^64 := by scalar_tac
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rw [hsh4, nat_shift63]; omega
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have hy4b : y4.val < 2^52 := by simp only [hy4]; exact hB3
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step as ⟨t4, ht4⟩
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step as ⟨w4, hw4⟩
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step as ⟨p4, back4, hpe4, hbk4⟩
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step as ⟨m4, hm4⟩
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try simp only [spec_ok]
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-- Iteration 5 (i = 4)
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apply loop_step
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simp only [backend.serial.u64.scalar.Scalar52.sub_loop.body,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut]
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step with range_next_lt_spec as ⟨o5, iter5, ho5, hs5, he5⟩
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simp only [ho5]
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step as ⟨x5, hx5⟩
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step as ⟨y5, hy5⟩
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simp [ha, hb, hs1, he1, hs2, he2, hs3, he3, hs4, he4] at hx5 hy5
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step as ⟨sh5, hsh5⟩
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have hsh5b : sh5.val ≤ 1 := by
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have h64 : w4.val < 2^64 := by scalar_tac
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rw [hsh5, nat_shift63]; omega
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have hy5b : y5.val < 2^52 := by simp only [hy5]; exact hB4
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step as ⟨t5, ht5⟩
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step as ⟨w5, hw5⟩
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step as ⟨p5, back5, hpe5, hbk5⟩
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step as ⟨m5, hm5⟩
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try simp only [spec_ok]
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-- Iteration 6: range exhausted, body returns done
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apply loop_step
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simp only [backend.serial.u64.scalar.Scalar52.sub_loop.body,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
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backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut]
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step with range_next_ge_spec as ⟨o6, iter6, ho6, hr6⟩
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simp only [ho6]
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try simp only [spec_ok]
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-- ── Final assembly: exhibit limbs m1..m5 and borrow bits w_k/2^63 ──
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-- Per-limb value facts. Limb 1 (borrow-in 0):
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have hshv1 : sh1.val = 0 := by rw [hsh1]; rfl
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have htv1 : t1.val = b0.val + 0 := by rw [ht1, hy1, hshv1]
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have hwv1 : w1.val = (a0.val + 2^64 - (b0.val + 0)) % 2^64 := by
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rw [hw1]; simp only [core.num.U64.wrapping_sub, UScalar.wrapping_sub_val_eq]
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have hsz : UScalar.size UScalarTy.U64 = 2^64 := by scalar_tac
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rw [hx1, htv1, hsz]; omega
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have hmv1 : m1.val = w1.val % 2^52 := by
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rw [hm1, UScalar.val_and, hmask, nat_and_mask52]
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have harith1 := sub_step_arith a0.val b0.val 0 hA0 hB0 (by omega)
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rw [← hwv1] at harith1
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-- Limb 2:
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have hshv2 : sh2.val = w1.val / 2^63 := by rw [hsh2, nat_shift63]
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have htv2 : t2.val = b1.val + w1.val / 2^63 := by rw [ht2, hy2, hshv2]
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have hwv2 : w2.val = (a1.val + 2^64 - (b1.val + w1.val / 2^63)) % 2^64 := by
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rw [hw2]; simp only [core.num.U64.wrapping_sub, UScalar.wrapping_sub_val_eq]
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have hsz : UScalar.size UScalarTy.U64 = 2^64 := by scalar_tac
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have h64w : w1.val < 2^64 := by scalar_tac
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rw [hx2, htv2, hsz]; omega
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have hmv2 : m2.val = w2.val % 2^52 := by
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rw [hm2, UScalar.val_and, hmask, nat_and_mask52]
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have harith2 := sub_step_arith a1.val b1.val (w1.val / 2^63) hA1 hB1 harith1.1
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rw [← hwv2] at harith2
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-- Limb 3:
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have hshv3 : sh3.val = w2.val / 2^63 := by rw [hsh3, nat_shift63]
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have htv3 : t3.val = b2.val + w2.val / 2^63 := by rw [ht3, hy3, hshv3]
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have hwv3 : w3.val = (a2.val + 2^64 - (b2.val + w2.val / 2^63)) % 2^64 := by
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rw [hw3]; simp only [core.num.U64.wrapping_sub, UScalar.wrapping_sub_val_eq]
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have hsz : UScalar.size UScalarTy.U64 = 2^64 := by scalar_tac
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have h64w : w2.val < 2^64 := by scalar_tac
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rw [hx3, htv3, hsz]; omega
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have hmv3 : m3.val = w3.val % 2^52 := by
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rw [hm3, UScalar.val_and, hmask, nat_and_mask52]
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have harith3 := sub_step_arith a2.val b2.val (w2.val / 2^63) hA2 hB2 harith2.1
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rw [← hwv3] at harith3
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-- Limb 4:
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have hshv4 : sh4.val = w3.val / 2^63 := by rw [hsh4, nat_shift63]
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have htv4 : t4.val = b3.val + w3.val / 2^63 := by rw [ht4, hy4, hshv4]
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have hwv4 : w4.val = (a3.val + 2^64 - (b3.val + w3.val / 2^63)) % 2^64 := by
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rw [hw4]; simp only [core.num.U64.wrapping_sub, UScalar.wrapping_sub_val_eq]
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have hsz : UScalar.size UScalarTy.U64 = 2^64 := by scalar_tac
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have h64w : w3.val < 2^64 := by scalar_tac
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rw [hx4, htv4, hsz]; omega
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have hmv4 : m4.val = w4.val % 2^52 := by
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rw [hm4, UScalar.val_and, hmask, nat_and_mask52]
|
||
have harith4 := sub_step_arith a3.val b3.val (w3.val / 2^63) hA3 hB3 harith3.1
|
||
rw [← hwv4] at harith4
|
||
-- Limb 5:
|
||
have hshv5 : sh5.val = w4.val / 2^63 := by rw [hsh5, nat_shift63]
|
||
have htv5 : t5.val = b4.val + w4.val / 2^63 := by rw [ht5, hy5, hshv5]
|
||
have hwv5 : w5.val = (a4.val + 2^64 - (b4.val + w4.val / 2^63)) % 2^64 := by
|
||
rw [hw5]; simp only [core.num.U64.wrapping_sub, UScalar.wrapping_sub_val_eq]
|
||
have hsz : UScalar.size UScalarTy.U64 = 2^64 := by scalar_tac
|
||
have h64w : w4.val < 2^64 := by scalar_tac
|
||
rw [hx5, htv5, hsz]; omega
|
||
have hmv5 : m5.val = w5.val % 2^52 := by
|
||
rw [hm5, UScalar.val_and, hmask, nat_and_mask52]
|
||
have harith5 := sub_step_arith a4.val b4.val (w4.val / 2^63) hA4 hB4 harith4.1
|
||
rw [← hwv5] at harith5
|
||
-- Witnesses and discharge
|
||
refine ⟨m1, m2, m3, m4, m5,
|
||
w1.val / 2^63, w2.val / 2^63, w3.val / 2^63, w4.val / 2^63, w5.val / 2^63,
|
||
?_, harith1.1, harith2.1, harith3.1, harith4.1, harith5.1,
|
||
by omega, by omega, by omega, by omega, by omega,
|
||
?_, ?_, ?_, ?_, ?_, nat_shift63 _⟩
|
||
· -- the result array is ZERO overwritten at 0..4 with m1..m5
|
||
simp [hbk1, hbk2, hbk3, hbk4, hbk5, Array.set_val_eq, ZERO_limbs,
|
||
hs1, hs2, hs3, hs4]
|
||
· rw [hmv1]; omega
|
||
· rw [hmv2]; omega
|
||
· rw [hmv3]; omega
|
||
· rw [hmv4]; omega
|
||
· rw [hmv5]; omega
|
||
|
||
|
||
|
||
/-- Step-spec for the `subtle` conditional select (faithful model). -/
|
||
theorem csel_step (a b : U64) (c : subtle.Choice) :
|
||
U64.Insts.SubtleConditionallySelectable.conditional_select a b c
|
||
⦃ r => r = (if c.val = 0 then a else b) ⦄ := by
|
||
unfold U64.Insts.SubtleConditionallySelectable.conditional_select
|
||
simp only [spec_ok]
|
||
|
||
/-! ### The conditional add of L, unrolled
|
||
|
||
`conditional_add_l(self, c)` adds `c ? L : 0` limb-wise with carry
|
||
propagation (Rust scalar.rs:193-204). Two cases, two lemmas: the Choice
|
||
invariant gives `c.val ∈ {0,1}` (the `subtle` model in
|
||
gen/CurveScalar/FunsExternal.lean). -/
|
||
|
||
/-- `conditional_add_l` with condition 0: identity on 52-bit-bounded limbs. -/
|
||
theorem cond_add_l_zero_spec (s : Sc) (c : subtle.Choice)
|
||
(s0 s1 s2 s3 s4 : U64)
|
||
(hs : (↑s : List U64) = [s0, s1, s2, s3, s4])
|
||
(hc : c.val = 0)
|
||
(hbnd : s0.val < 2^52 ∧ s1.val < 2^52 ∧ s2.val < 2^52 ∧ s3.val < 2^52 ∧ s4.val < 2^52) :
|
||
backend.serial.u64.scalar.Scalar52.conditional_add_l s c
|
||
⦃ (cw : U64 × Sc) => ∃ r0 r1 r2 r3 r4 : U64,
|
||
(↑cw.2 : List U64) = [r0, r1, r2, r3, r4] ∧
|
||
r0.val = s0.val ∧ r1.val = s1.val ∧ r2.val = s2.val ∧
|
||
r3.val = s3.val ∧ r4.val = s4.val ⦄ := by
|
||
obtain ⟨hS0, hS1, hS2, hS3, hS4⟩ := hbnd
|
||
unfold backend.serial.u64.scalar.Scalar52.conditional_add_l
|
||
step as ⟨sh, hsh⟩
|
||
step as ⟨mask, hmask⟩
|
||
have hmaskv : mask.val = 2^52 - 1 := by
|
||
simp [hmask, hsh, U64.size_def, U64.numBits]
|
||
unfold backend.serial.u64.scalar.Scalar52.conditional_add_l_loop
|
||
-- Iteration 1 (i = 0, carry-in 0, addend 0)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
U64.Insts.SubtleConditionallySelectable.conditional_select,
|
||
hc, reduceIte, bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o1, iter1, ho1, hs1, he1⟩
|
||
simp only [ho1]
|
||
step as ⟨l1, hl1⟩
|
||
step as ⟨g1, hg1⟩
|
||
step as ⟨u1, hu1⟩
|
||
simp [hs] at hu1
|
||
step as ⟨v1, hv1⟩
|
||
step as ⟨cy1, hcy1⟩
|
||
step as ⟨q1, bk1, hq1, hbk1⟩
|
||
step as ⟨r1, hr1⟩
|
||
try simp only [spec_ok]
|
||
have hgv1 : g1.val = 0 := by rw [hg1]; rfl
|
||
have hcyv1 : cy1.val = s0.val := by rw [hcy1, hv1, hu1, hgv1]; simp
|
||
have hcyb1 : cy1.val < 2^52 := by rw [hcyv1]; exact hS0
|
||
have hrv1 : r1.val = s0.val := by
|
||
rw [hr1, UScalar.val_and, hmaskv, nat_and_mask52, hcyv1, Nat.mod_eq_of_lt hS0]
|
||
-- Iteration 2 (i = 1)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
U64.Insts.SubtleConditionallySelectable.conditional_select,
|
||
hc, reduceIte, bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o2, iter2, ho2, hs2, he2⟩
|
||
simp only [ho2]
|
||
step as ⟨l2, hl2⟩
|
||
step as ⟨g2, hg2⟩
|
||
step as ⟨u2, hu2⟩
|
||
simp [hbk1, Array.set_val_eq, hs, hs1, he1] at hu2
|
||
have hgv2 : g2.val = 0 := by rw [hg2, nat_shift52, hcyv1]; omega
|
||
step as ⟨v2, hv2⟩
|
||
step as ⟨cy2, hcy2⟩
|
||
step as ⟨q2, bk2, hq2, hbk2⟩
|
||
step as ⟨r2, hr2⟩
|
||
try simp only [spec_ok]
|
||
have hcyv2 : cy2.val = s1.val := by rw [hcy2, hv2, hu2, hgv2]; simp
|
||
have hcyb2 : cy2.val < 2^52 := by rw [hcyv2]; exact hS1
|
||
have hrv2 : r2.val = s1.val := by
|
||
rw [hr2, UScalar.val_and, hmaskv, nat_and_mask52, hcyv2, Nat.mod_eq_of_lt hS1]
|
||
-- Iteration 3 (i = 2)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
U64.Insts.SubtleConditionallySelectable.conditional_select,
|
||
hc, reduceIte, bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o3, iter3, ho3, hs3, he3⟩
|
||
simp only [ho3]
|
||
step as ⟨l3, hl3⟩
|
||
step as ⟨g3, hg3⟩
|
||
step as ⟨u3, hu3⟩
|
||
simp [hbk1, hbk2, Array.set_val_eq, hs, hs1, he1, hs2, he2] at hu3
|
||
have hgv3 : g3.val = 0 := by rw [hg3, nat_shift52, hcyv2]; omega
|
||
step as ⟨v3, hv3⟩
|
||
step as ⟨cy3, hcy3⟩
|
||
step as ⟨q3, bk3, hq3, hbk3⟩
|
||
step as ⟨r3, hr3⟩
|
||
try simp only [spec_ok]
|
||
have hcyv3 : cy3.val = s2.val := by rw [hcy3, hv3, hu3, hgv3]; simp
|
||
have hcyb3 : cy3.val < 2^52 := by rw [hcyv3]; exact hS2
|
||
have hrv3 : r3.val = s2.val := by
|
||
rw [hr3, UScalar.val_and, hmaskv, nat_and_mask52, hcyv3, Nat.mod_eq_of_lt hS2]
|
||
-- Iteration 4 (i = 3)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
U64.Insts.SubtleConditionallySelectable.conditional_select,
|
||
hc, reduceIte, bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o4, iter4, ho4, hs4, he4⟩
|
||
simp only [ho4]
|
||
step as ⟨l4, hl4⟩
|
||
step as ⟨g4, hg4⟩
|
||
step as ⟨u4, hu4⟩
|
||
simp [hbk1, hbk2, hbk3, Array.set_val_eq, hs, hs1, he1, hs2, he2, hs3, he3] at hu4
|
||
have hgv4 : g4.val = 0 := by rw [hg4, nat_shift52, hcyv3]; omega
|
||
step as ⟨v4, hv4⟩
|
||
step as ⟨cy4, hcy4⟩
|
||
step as ⟨q4, bk4, hq4, hbk4⟩
|
||
step as ⟨r4, hr4⟩
|
||
try simp only [spec_ok]
|
||
have hcyv4 : cy4.val = s3.val := by rw [hcy4, hv4, hu4, hgv4]; simp
|
||
have hcyb4 : cy4.val < 2^52 := by rw [hcyv4]; exact hS3
|
||
have hrv4 : r4.val = s3.val := by
|
||
rw [hr4, UScalar.val_and, hmaskv, nat_and_mask52, hcyv4, Nat.mod_eq_of_lt hS3]
|
||
-- Iteration 5 (i = 4)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
U64.Insts.SubtleConditionallySelectable.conditional_select,
|
||
hc, reduceIte, bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o5, iter5, ho5, hs5, he5⟩
|
||
simp only [ho5]
|
||
step as ⟨l5, hl5⟩
|
||
step as ⟨g5, hg5⟩
|
||
step as ⟨u5, hu5⟩
|
||
simp [hbk1, hbk2, hbk3, hbk4, Array.set_val_eq, hs, hs1, he1, hs2, he2, hs3, he3,
|
||
hs4, he4] at hu5
|
||
have hgv5 : g5.val = 0 := by rw [hg5, nat_shift52, hcyv4]; omega
|
||
step as ⟨v5, hv5⟩
|
||
step as ⟨cy5, hcy5⟩
|
||
step as ⟨q5, bk5, hq5, hbk5⟩
|
||
step as ⟨r5, hr5⟩
|
||
try simp only [spec_ok]
|
||
have hcyv5 : cy5.val = s4.val := by rw [hcy5, hv5, hu5, hgv5]; simp
|
||
have hrv5 : r5.val = s4.val := by
|
||
rw [hr5, UScalar.val_and, hmaskv, nat_and_mask52, hcyv5, Nat.mod_eq_of_lt hS4]
|
||
-- Iteration 6: exhausted
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body]
|
||
step with range_next_ge_spec as ⟨o6, iter6, ho6, hr6⟩
|
||
simp only [ho6]
|
||
try simp only [spec_ok]
|
||
refine ⟨r1, r2, r3, r4, r5, ?_, hrv1, hrv2, hrv3, hrv4, hrv5⟩
|
||
simp [hbk1, hbk2, hbk3, hbk4, hbk5, Array.set_val_eq, hs,
|
||
hs1, hs2, hs3, hs4]
|
||
|
||
|
||
/-- `conditional_add_l` with condition 1: adds L limb-wise with carry.
|
||
Proven by the same borrow/carry-loop technique as `sub_loop_spec`, with
|
||
the addend stepped as its own value (`ad_i = L[i]`) rather than folded,
|
||
so the `index_mut` write-back matches `sub_loop_spec`'s working pattern. -/
|
||
theorem cond_add_l_one_spec (s : Sc) (c : subtle.Choice)
|
||
(s0 s1 s2 s3 s4 : U64)
|
||
(hs : (↑s : List U64) = [s0, s1, s2, s3, s4])
|
||
(hc : c.val = 1)
|
||
(hbnd : s0.val < 2^52 ∧ s1.val < 2^52 ∧ s2.val < 2^52 ∧ s3.val < 2^52 ∧ s4.val < 2^52) :
|
||
backend.serial.u64.scalar.Scalar52.conditional_add_l s c
|
||
⦃ (cw : U64 × Sc) => ∃ r0 r1 r2 r3 r4 : U64, ∃ γ1 γ2 γ3 γ4 γ5 : ℕ,
|
||
(↑cw.2 : List U64) = [r0, r1, r2, r3, r4] ∧
|
||
γ1 ≤ 1 ∧ γ2 ≤ 1 ∧ γ3 ≤ 1 ∧ γ4 ≤ 1 ∧ γ5 ≤ 1 ∧
|
||
r0.val < 2^52 ∧ r1.val < 2^52 ∧ r2.val < 2^52 ∧ r3.val < 2^52 ∧ r4.val < 2^52 ∧
|
||
r0.val + 2^52 * γ1 = s0.val + 671914833335277 ∧
|
||
r1.val + 2^52 * γ2 = s1.val + 3916664325105025 + γ1 ∧
|
||
r2.val + 2^52 * γ3 = s2.val + 1367801 + γ2 ∧
|
||
r3.val + 2^52 * γ4 = s3.val + 0 + γ3 ∧
|
||
r4.val + 2^52 * γ5 = s4.val + 17592186044416 + γ4 ⦄ := by
|
||
obtain ⟨hS0, hS1, hS2, hS3, hS4⟩ := hbnd
|
||
unfold backend.serial.u64.scalar.Scalar52.conditional_add_l
|
||
step as ⟨sh, hsh⟩
|
||
step as ⟨mask, hmask⟩
|
||
have hmaskv : mask.val = 2^52 - 1 := by
|
||
simp [hmask, hsh, U64.size_def, U64.numBits]
|
||
unfold backend.serial.u64.scalar.Scalar52.conditional_add_l_loop
|
||
-- Iteration 1 (i = 0, L[0] = 671914833335277)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o1, iter1, ho1, hs1, he1⟩
|
||
simp only [ho1]
|
||
step as ⟨l1, hl1⟩
|
||
simp [L_limbs] at hl1
|
||
step with csel_step as ⟨ad1, had1⟩
|
||
rw [hc] at had1; norm_num at had1
|
||
have hadv1 : ad1.val = 671914833335277 := by rw [had1, hl1]; rfl
|
||
step as ⟨g1, hg1⟩
|
||
have hgb1 : g1.val = 0 := by rw [hg1]; rfl
|
||
step as ⟨u1, hu1⟩
|
||
simp [hs] at hu1
|
||
have hub1 : u1.val < 2^52 := by rw [hu1]; exact hS0
|
||
step as ⟨v1, hv1⟩
|
||
have hvv1 : v1.val = u1.val := by rw [hv1, hgb1]; simp
|
||
step as ⟨cy1, hcy1⟩
|
||
have hcyv1 : cy1.val = u1.val + 671914833335277 := by rw [hcy1, hvv1, hadv1]
|
||
have hcyb1 : cy1.val < 2^53 := by rw [hcyv1]; omega
|
||
step as ⟨q1, bk1, hq1, hbk1⟩
|
||
step as ⟨r1, hr1⟩
|
||
try simp only [spec_ok]
|
||
have hrv1 : r1.val = cy1.val % 2^52 := by
|
||
rw [hr1, UScalar.val_and, hmaskv, nat_and_mask52]
|
||
-- Iteration 2 (i = 1, L[1] = 3916664325105025)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o2, iter2, ho2, hs2, he2⟩
|
||
simp only [ho2]
|
||
step as ⟨l2, hl2⟩
|
||
simp [L_limbs, hs1, he1] at hl2
|
||
step with csel_step as ⟨ad2, had2⟩
|
||
rw [hc] at had2; norm_num at had2
|
||
have hadv2 : ad2.val = 3916664325105025 := by rw [had2, hl2]; rfl
|
||
step as ⟨g2, hg2⟩
|
||
have hgeq2 : g2.val = cy1.val / 2^52 := by rw [hg2, nat_shift52]
|
||
have hgb2 : g2.val ≤ 1 := by rw [hgeq2]; omega
|
||
step as ⟨u2, hu2⟩
|
||
simp [hbk1, Array.set_val_eq, hs, hs1, he1] at hu2
|
||
have hub2 : u2.val < 2^52 := by rw [hu2]; exact hS1
|
||
step as ⟨v2, hv2⟩
|
||
have hvv2 : v2.val = g2.val + u2.val := by rw [hv2]
|
||
step as ⟨cy2, hcy2⟩
|
||
have hcyv2 : cy2.val = g2.val + u2.val + 3916664325105025 := by rw [hcy2, hvv2, hadv2]
|
||
have hcyb2 : cy2.val < 2^53 := by rw [hcyv2]; omega
|
||
step as ⟨q2, bk2, hq2, hbk2⟩
|
||
step as ⟨r2, hr2⟩
|
||
try simp only [spec_ok]
|
||
have hrv2 : r2.val = cy2.val % 2^52 := by
|
||
rw [hr2, UScalar.val_and, hmaskv, nat_and_mask52]
|
||
-- Iteration 3 (i = 2, L[2] = 1367801)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o3, iter3, ho3, hs3, he3⟩
|
||
simp only [ho3]
|
||
step as ⟨l3, hl3⟩
|
||
simp [L_limbs, hs1, he1, hs2, he2] at hl3
|
||
step with csel_step as ⟨ad3, had3⟩
|
||
rw [hc] at had3; norm_num at had3
|
||
have hadv3 : ad3.val = 1367801 := by rw [had3, hl3]; rfl
|
||
step as ⟨g3, hg3⟩
|
||
have hgeq3 : g3.val = cy2.val / 2^52 := by rw [hg3, nat_shift52]
|
||
have hgb3 : g3.val ≤ 1 := by rw [hgeq3]; omega
|
||
step as ⟨u3, hu3⟩
|
||
simp [hbk1, hbk2, Array.set_val_eq, hs, hs1, he1, hs2, he2] at hu3
|
||
have hub3 : u3.val < 2^52 := by rw [hu3]; exact hS2
|
||
step as ⟨v3, hv3⟩
|
||
have hvv3 : v3.val = g3.val + u3.val := by rw [hv3]
|
||
step as ⟨cy3, hcy3⟩
|
||
have hcyv3 : cy3.val = g3.val + u3.val + 1367801 := by rw [hcy3, hvv3, hadv3]
|
||
have hcyb3 : cy3.val < 2^53 := by rw [hcyv3]; omega
|
||
step as ⟨q3, bk3, hq3, hbk3⟩
|
||
step as ⟨r3, hr3⟩
|
||
try simp only [spec_ok]
|
||
have hrv3 : r3.val = cy3.val % 2^52 := by
|
||
rw [hr3, UScalar.val_and, hmaskv, nat_and_mask52]
|
||
-- Iteration 4 (i = 3, L[3] = 0)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o4, iter4, ho4, hs4, he4⟩
|
||
simp only [ho4]
|
||
step as ⟨l4, hl4⟩
|
||
simp [L_limbs, hs1, he1, hs2, he2, hs3, he3] at hl4
|
||
step with csel_step as ⟨ad4, had4⟩
|
||
rw [hc] at had4; norm_num at had4
|
||
have hadv4 : ad4.val = 0 := by rw [had4, hl4]; rfl
|
||
step as ⟨g4, hg4⟩
|
||
have hgeq4 : g4.val = cy3.val / 2^52 := by rw [hg4, nat_shift52]
|
||
have hgb4 : g4.val ≤ 1 := by rw [hgeq4]; omega
|
||
step as ⟨u4, hu4⟩
|
||
simp [hbk1, hbk2, hbk3, Array.set_val_eq, hs, hs1, he1, hs2, he2, hs3, he3] at hu4
|
||
have hub4 : u4.val < 2^52 := by rw [hu4]; exact hS3
|
||
step as ⟨v4, hv4⟩
|
||
have hvv4 : v4.val = g4.val + u4.val := by rw [hv4]
|
||
step as ⟨cy4, hcy4⟩
|
||
have hcyv4 : cy4.val = g4.val + u4.val + 0 := by rw [hcy4, hvv4, hadv4]
|
||
have hcyb4 : cy4.val < 2^53 := by rw [hcyv4]; omega
|
||
step as ⟨q4, bk4, hq4, hbk4⟩
|
||
step as ⟨r4, hr4⟩
|
||
try simp only [spec_ok]
|
||
have hrv4 : r4.val = cy4.val % 2^52 := by
|
||
rw [hr4, UScalar.val_and, hmaskv, nat_and_mask52]
|
||
-- Iteration 5 (i = 4, L[4] = 17592186044416)
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexUsizeU64.index,
|
||
backend.serial.u64.scalar.Scalar52.Insts.CoreOpsIndexIndexMutUsizeU64.index_mut,
|
||
bind_tc_ok]
|
||
step with range_next_lt_spec as ⟨o5, iter5, ho5, hs5, he5⟩
|
||
simp only [ho5]
|
||
step as ⟨l5, hl5⟩
|
||
simp [L_limbs, hs1, he1, hs2, he2, hs3, he3, hs4, he4] at hl5
|
||
step with csel_step as ⟨ad5, had5⟩
|
||
rw [hc] at had5; norm_num at had5
|
||
have hadv5 : ad5.val = 17592186044416 := by rw [had5, hl5]; rfl
|
||
step as ⟨g5, hg5⟩
|
||
have hgeq5 : g5.val = cy4.val / 2^52 := by rw [hg5, nat_shift52]
|
||
have hgb5 : g5.val ≤ 1 := by rw [hgeq5]; omega
|
||
step as ⟨u5, hu5⟩
|
||
simp [hbk1, hbk2, hbk3, hbk4, Array.set_val_eq, hs, hs1, he1, hs2, he2, hs3, he3, hs4, he4] at hu5
|
||
have hub5 : u5.val < 2^52 := by rw [hu5]; exact hS4
|
||
step as ⟨v5, hv5⟩
|
||
have hvv5 : v5.val = g5.val + u5.val := by rw [hv5]
|
||
step as ⟨cy5, hcy5⟩
|
||
have hcyv5 : cy5.val = g5.val + u5.val + 17592186044416 := by rw [hcy5, hvv5, hadv5]
|
||
have hcyb5 : cy5.val < 2^53 := by rw [hcyv5]; omega
|
||
step as ⟨q5, bk5, hq5, hbk5⟩
|
||
step as ⟨r5, hr5⟩
|
||
try simp only [spec_ok]
|
||
have hrv5 : r5.val = cy5.val % 2^52 := by
|
||
rw [hr5, UScalar.val_and, hmaskv, nat_and_mask52]
|
||
-- Iteration 6: exhausted
|
||
apply loop_step
|
||
simp only [backend.serial.u64.scalar.Scalar52.conditional_add_l_loop.body]
|
||
step with range_next_ge_spec as ⟨o6, iter6, ho6, hr6⟩
|
||
simp only [ho6]
|
||
try simp only [spec_ok]
|
||
refine ⟨r1, r2, r3, r4, r5,
|
||
cy1.val / 2^52, cy2.val / 2^52, cy3.val / 2^52, cy4.val / 2^52, cy5.val / 2^52,
|
||
?_, by omega, by omega, by omega, by omega, by omega,
|
||
by rw [hrv1]; omega, by rw [hrv2]; omega, by rw [hrv3]; omega,
|
||
by rw [hrv4]; omega, by rw [hrv5]; omega,
|
||
?_, ?_, ?_, ?_, ?_⟩
|
||
· simp [hbk1, hbk2, hbk3, hbk4, hbk5, Array.set_val_eq, hs, hs1, hs2, hs3, hs4]
|
||
· rw [hrv1, hcyv1, hu1]; omega
|
||
· rw [hrv2, hcyv2, hu2, hgeq2]; omega
|
||
· rw [hrv3, hcyv3, hu3, hgeq3]; omega
|
||
· rw [hrv4, hcyv4, hu4, hgeq4]; omega
|
||
· rw [hrv5, hcyv5, hu5, hgeq5]; omega
|
||
|
||
/-- Telescoping the five borrow equations to the value level (ℕ).
|
||
Given the per-limb identities d_i + b_i + β_i = a_i + 2^52·β_{i+1}
|
||
(β_0 = 0), the weighted sum gives
|
||
scLimbs d + scLimbs b = scLimbs a + 2^260·β5.
|
||
Coefficients reach 2^260; stated as an explicit linear identity so the
|
||
kernel checks (never searches) it — the METHOD-4 discipline. -/
|
||
theorem sub_telescope
|
||
(d0 d1 d2 d3 d4 b0 b1 b2 b3 b4 a0 a1 a2 a3 a4 : ℕ)
|
||
(β1 β2 β3 β4 β5 : ℕ)
|
||
(e0 : d0 + b0 = a0 + 2^52 * β1)
|
||
(e1 : d1 + b1 + β1 = a1 + 2^52 * β2)
|
||
(e2 : d2 + b2 + β2 = a2 + 2^52 * β3)
|
||
(e3 : d3 + b3 + β3 = a3 + 2^52 * β4)
|
||
(e4 : d4 + b4 + β4 = a4 + 2^52 * β5) :
|
||
(d0 + 2^52*d1 + 2^104*d2 + 2^156*d3 + 2^208*d4)
|
||
+ (b0 + 2^52*b1 + 2^104*b2 + 2^156*b3 + 2^208*b4)
|
||
= (a0 + 2^52*a1 + 2^104*a2 + 2^156*a3 + 2^208*a4) + 2^260 * β5 := by
|
||
omega
|
||
|
||
/-- Telescoping the conditional-add carry chain (same shape as `sub_telescope`):
|
||
r_i + 2^52·γ_{i+1} = s_i + c_i + γ_i (γ_0 = 0) sums to
|
||
scLimbs r + 2^260·γ5 = scLimbs s + scLimbs c. -/
|
||
theorem add_telescope
|
||
(r0 r1 r2 r3 r4 s0 s1 s2 s3 s4 c0 c1 c2 c3 c4 : ℕ)
|
||
(γ1 γ2 γ3 γ4 γ5 : ℕ)
|
||
(e0 : r0 + 2^52 * γ1 = s0 + c0)
|
||
(e1 : r1 + 2^52 * γ2 = s1 + c1 + γ1)
|
||
(e2 : r2 + 2^52 * γ3 = s2 + c2 + γ2)
|
||
(e3 : r3 + 2^52 * γ4 = s3 + c3 + γ3)
|
||
(e4 : r4 + 2^52 * γ5 = s4 + c4 + γ4) :
|
||
(r0 + 2^52*r1 + 2^104*r2 + 2^156*r3 + 2^208*r4) + 2^260 * γ5
|
||
= (s0 + 2^52*s1 + 2^104*s2 + 2^156*s3 + 2^208*s4)
|
||
+ (c0 + 2^52*c1 + 2^104*c2 + 2^156*c3 + 2^208*c4) := by
|
||
omega
|
||
|
||
/-! ### Top-level subtraction value spec -/
|
||
|
||
/-- **Scalar subtraction is correct mod ℓ.** For limb-bounded inputs with
|
||
canonical subtrahend (scVal b < ℓ), the transpiled `Scalar52::sub`
|
||
denotes ⟦a⟧ − ⟦b⟧ in `ZMod ℓ`. Assembly of `sub_loop_spec` (borrow
|
||
chain) and `cond_add_l_{zero,one}_spec` (conditional +ℓ) through the
|
||
two telescopes; the bind is applied manually via `spec_bind` to keep
|
||
full control of the postcondition destructuring. -/
|
||
theorem sub_val_spec (a b : Sc)
|
||
(a0 a1 a2 a3 a4 b0 b1 b2 b3 b4 : U64)
|
||
(ha : (↑a : List U64) = [a0, a1, a2, a3, a4])
|
||
(hb : (↑b : List U64) = [b0, b1, b2, b3, b4])
|
||
(hab : a0.val < 2^52 ∧ a1.val < 2^52 ∧ a2.val < 2^52 ∧ a3.val < 2^52 ∧ a4.val < 2^52)
|
||
(hbb : b0.val < 2^52 ∧ b1.val < 2^52 ∧ b2.val < 2^52 ∧ b3.val < 2^52 ∧ b4.val < 2^52)
|
||
(hcb : scVal b < Ell) :
|
||
backend.serial.u64.scalar.Scalar52.sub a b
|
||
⦃ r => scDenote r = scDenote a - scDenote b ⦄ := by
|
||
obtain ⟨hA0, hA1, hA2, hA3, hA4⟩ := hab
|
||
obtain ⟨hB0, hB1, hB2, hB3, hB4⟩ := hbb
|
||
unfold backend.serial.u64.scalar.Scalar52.sub
|
||
step as ⟨sh, hsh⟩
|
||
step as ⟨mask, hmask⟩
|
||
have hmaskv : mask.val = 2^52 - 1 := by
|
||
simp [hmask, hsh, U64.size_def, U64.numBits]
|
||
-- bind the borrow loop manually
|
||
apply spec_bind (sub_loop_spec a b mask a0 a1 a2 a3 a4 b0 b1 b2 b3 b4 ha hb hmaskv
|
||
⟨hA0, hA1, hA2, hA3, hA4, hB0, hB1, hB2, hB3, hB4⟩)
|
||
rintro ⟨dw, w⟩ ⟨d0, d1, d2, d3, d4, β1, β2, β3, β4, β5, hdl,
|
||
hβ1, hβ2, hβ3, hβ4, hβ5, hd0, hd1, hd2, hd3, hd4,
|
||
he0, he1, he2, he3, he4, hbor⟩
|
||
simp only at hdl hbor
|
||
show (do
|
||
let i1 ← w >>> 63#i32
|
||
let i2 ← lift (UScalar.cast UScalarTy.U8 i1)
|
||
let c ← subtle.Choice.Insts.CoreConvertFromU8.from i2
|
||
let (_, difference1) ← dw.conditional_add_l c
|
||
ok difference1) ⦃ r => scDenote r = scDenote a - scDenote b ⦄
|
||
-- borrow >>> 63, cast, Choice
|
||
step as ⟨i1, hi1⟩
|
||
have hi1v : i1.val = β5 := by rw [hi1]; exact hbor
|
||
step as ⟨i2, hi2⟩
|
||
-- Choice.from is the identity model; inline c := i2
|
||
simp only [subtle.Choice.Insts.CoreConvertFromU8.from, bind_tc_ok]
|
||
set cc := i2 with hccdef
|
||
have hccv : cc.val = β5 := by
|
||
have hb5 : β5 < 2^8 := by omega
|
||
rw [hi2, UScalar.cast_val_eq, hi1v]
|
||
simp only [UScalarTy.U8, UScalarTy.numBits]
|
||
omega
|
||
have hdb : d0.val < 2^52 ∧ d1.val < 2^52 ∧ d2.val < 2^52 ∧ d3.val < 2^52 ∧ d4.val < 2^52 :=
|
||
⟨hd0, hd1, hd2, hd3, hd4⟩
|
||
have hTsub : scLimbs d0 d1 d2 d3 d4 + scLimbs b0 b1 b2 b3 b4
|
||
= scLimbs a0 a1 a2 a3 a4 + 2^260 * β5 := by
|
||
unfold scLimbs
|
||
exact sub_telescope _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ he0 he1 he2 he3 he4
|
||
have hsva : scVal a = scLimbs a0 a1 a2 a3 a4 := scVal_eq a a0 a1 a2 a3 a4 ha
|
||
have hsvb : scVal b = scLimbs b0 b1 b2 b3 b4 := scVal_eq b b0 b1 b2 b3 b4 hb
|
||
rcases (Nat.le_one_iff_eq_zero_or_eq_one.mp hβ5) with hβz | hβo
|
||
· -- β5 = 0: no underflow, cond-add is identity on values
|
||
have hc0 : cc.val = 0 := by rw [hccv, hβz]
|
||
apply spec_bind (cond_add_l_zero_spec dw cc d0 d1 d2 d3 d4 hdl hc0 hdb)
|
||
rintro ⟨cw1, cw2⟩ ⟨r0, r1, r2, r3, r4, hrl, hr0, hr1, hr2, hr3, hr4⟩
|
||
simp only at hrl
|
||
show scDenote cw2 = scDenote a - scDenote b
|
||
have hcwval : scVal cw2 = scLimbs d0 d1 d2 d3 d4 := by
|
||
rw [scVal_eq cw2 r0 r1 r2 r3 r4 hrl]; unfold scLimbs; rw [hr0, hr1, hr2, hr3, hr4]
|
||
have key : scVal cw2 + scVal b = scVal a := by
|
||
rw [hcwval, hsva, hsvb]; rw [hβz] at hTsub; simpa using hTsub
|
||
have hc := congrArg (Nat.cast (R := ZMod Ell)) key
|
||
push_cast at hc
|
||
simp only [scDenote]; rw [eq_sub_iff_add_eq]; exact hc
|
||
· -- β5 = 1: underflow; +ℓ, and the 2^260 wrap cancels in ZMod ℓ
|
||
have hc1 : cc.val = 1 := by rw [hccv, hβo]
|
||
apply spec_bind (cond_add_l_one_spec dw cc d0 d1 d2 d3 d4 hdl hc1 hdb)
|
||
rintro ⟨cw1, cw2⟩ ⟨r0, r1, r2, r3, r4, γ1, γ2, γ3, γ4, γ5, hrl,
|
||
hgb1, hgb2, hgb3, hgb4, hgb5, hrb0, hrb1, hrb2, hrb3, hrb4,
|
||
hf0, hf1, hf2, hf3, hf4⟩
|
||
simp only at hrl
|
||
show scDenote cw2 = scDenote a - scDenote b
|
||
have hLsum : (671914833335277 + 2^52*3916664325105025 + 2^104*1367801
|
||
+ 2^156*0 + 2^208*17592186044416 : ℕ) = Ell := by unfold Ell; norm_num
|
||
have hTadd : scLimbs r0 r1 r2 r3 r4 + 2^260 * γ5 = scLimbs d0 d1 d2 d3 d4 + Ell := by
|
||
have h := add_telescope r0.val r1.val r2.val r3.val r4.val
|
||
d0.val d1.val d2.val d3.val d4.val
|
||
671914833335277 3916664325105025 1367801 0 17592186044416
|
||
γ1 γ2 γ3 γ4 γ5 hf0 hf1 hf2 hf3 hf4
|
||
unfold scLimbs; rw [← hLsum]; linear_combination h
|
||
have hblt : scLimbs b0 b1 b2 b3 b4 < Ell := by rw [← hsvb]; exact hcb
|
||
-- γ5 = 1, derived with scLimbs kept as opaque atoms (no 2^52i unfold →
|
||
-- omega stays cheap: 4 atoms + one 2^260 literal + Ell as an atom)
|
||
have hrlt : scLimbs r0 r1 r2 r3 r4 < 2^260 := by unfold scLimbs; omega
|
||
have hd_eq : scLimbs d0 d1 d2 d3 d4 + scLimbs b0 b1 b2 b3 b4
|
||
= scLimbs a0 a1 a2 a3 a4 + 2^260 := by rw [hβo] at hTsub; simpa using hTsub
|
||
have hγ5 : γ5 = 1 := by
|
||
-- atoms: R,D,B,A := scLimbs …, Ell; facts below force γ5 = 1
|
||
have hRnn : 0 ≤ scLimbs a0 a1 a2 a3 a4 := Nat.zero_le _
|
||
omega
|
||
have hc := congrArg (Nat.cast (R := ZMod Ell)) hTadd
|
||
have hc2 := congrArg (Nat.cast (R := ZMod Ell)) hTsub
|
||
have hEz : (Ell : ZMod Ell) = 0 := ZMod.natCast_self Ell
|
||
simp only [scDenote, scVal_eq cw2 r0 r1 r2 r3 r4 hrl, hsva, hsvb, hβo, hγ5]
|
||
rw [hγ5] at hc
|
||
rw [hβo] at hc2
|
||
push_cast at hc hc2 ⊢
|
||
rw [hEz] at hc
|
||
linear_combination hc + hc2
|
||
|
||
end ScalarProofs
|