From 089efbbbbe91c2cf97a00cb19711e3d2e76667b1 Mon Sep 17 00:00:00 2001
From: Henry de Valence <hdevalence@chain.com>
Date: Mon, 30 Oct 2017 16:52:27 -0700
Subject: [PATCH] Prune constants that are no longer used anywhere

---
 src/constants.rs       | 40 ----------------------------------------
 src/constants_32bit.rs | 37 -------------------------------------
 src/constants_64bit.rs | 22 ----------------------
 3 files changed, 99 deletions(-)

diff --git a/src/constants.rs b/src/constants.rs
index 09880dd..86a71a5 100644
--- a/src/constants.rs
+++ b/src/constants.rs
@@ -28,20 +28,6 @@ pub use constants_64bit::*;
 #[cfg(not(feature="radix_51"))]
 pub use constants_32bit::*;
 
-/// (p-1)/2, in little-endian bytes.
-pub const HALF_P_MINUS_1_BYTES: [u8; 32] =
-    [0xf6, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-     0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-     0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-     0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x3f];
-
-/// `HALF_Q_MINUS_1_BYTES` is (2^255-20)/2 expressed in little endian form.
-pub const HALF_Q_MINUS_1_BYTES: [u8; 32] = [ // halfQMinus1Bytes
-    0xf6, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x3f, ];
-
 /// Basepoint has y = 4/5.
 ///
 /// Generated with Sage: these are the bytes of 4/5 in 𝔽_p.  The
@@ -123,13 +109,6 @@ mod test {
         }
     }
 
-    #[test]
-    fn test_half() {
-        let one = FieldElement::one();
-        let two = &one + &one;
-        assert_eq!(one, &two * &constants::HALF);
-    }
-
     /// Test that the constant for sqrt(-486664) really is a square
     /// root of -486664.
     #[test]
@@ -204,14 +183,6 @@ mod test {
         assert_eq!(d2, constants::d2);
     }
 
-    #[test]
-    fn test_d4() {
-        let mut four = FieldElement::zero();
-        // XXX should have a way to create small field elements
-        four.0[0] = 4;
-        assert_eq!(&constants::d * &four, constants::d4);
-    }
-
     #[test]
     fn test_sqrt_ad_minus_one() {
         let a = FieldElement::minus_one();
@@ -220,15 +191,4 @@ mod test {
         assert_eq!(should_be_ad_minus_one, ad_minus_one);
     }
 
-    #[test]
-    fn test_a_minus_d() {
-        let a = FieldElement::minus_one();
-        let a_minus_d = &a - &constants::d;
-        assert_eq!(a_minus_d, constants::a_minus_d);
-        let (_, invsqrt_a_minus_d) = constants::a_minus_d.invsqrt();
-        assert_eq!(invsqrt_a_minus_d, constants::invsqrt_a_minus_d);
-        let inv_a_minus_d = invsqrt_a_minus_d.square();
-        assert_eq!(inv_a_minus_d, constants::inv_a_minus_d);
-        assert_eq!(&inv_a_minus_d * &a_minus_d, FieldElement::one());
-    }
 }
diff --git a/src/constants_32bit.rs b/src/constants_32bit.rs
index 6cbe4db..fd86cd1 100644
--- a/src/constants_32bit.rs
+++ b/src/constants_32bit.rs
@@ -31,14 +31,6 @@ pub const d2: FieldElement32      = FieldElement32([
     -21827239,  -5839606, -30745221,  13898782,    229458,
     15978800,  -12551817,  -6495438,  29715968,   9444199, ]);
 
-pub const d4: FieldElement32      = FieldElement32([
-    23454405,  -11679213,   5618422,  -5756869,    458917,
-    -1596832,  -25103633, -12990876,  -7676928, -14666033  ]);
-
-pub const a_minus_d: FieldElement32    = FieldElement32([
-    10913609,  -13857413,  15372611,  -6949391,   -114729,
-     8787816,    6275908,   3247719,  18696448,  12055116, ]);
-
 pub const sqrt_ad_minus_one: FieldElement32 = FieldElement32([
     24849947, -153582, -23613485, 6347715, -21072328, -667138, -25271143, -15367704, -870347, 14525639
 ]);
@@ -48,18 +40,6 @@ pub const invsqrt_a_minus_d: FieldElement32 = FieldElement32([
     120897, 20826367, -7060776, 6093568, -1986012
 ]);
 
-#[cfg(not(feature="radix_51"))]
-pub const inv_a_minus_d: FieldElement32 = FieldElement32([
-    -121666, 0, 0, 0, 0, 0, 0, 0, 0, 0
-]);
-
-/// (p-1)/2, in little-endian bytes.
-pub const HALF_P_MINUS_1_BYTES: [u8; 32] =
-    [0xf6, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-     0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-     0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-     0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x3f];
-
 /// Precomputed value of one of the square roots of -1 (mod p)
 pub const SQRT_M1: FieldElement32 = FieldElement32([
     -32595792,  -7943725,   9377950,   3500415,  12389472,
@@ -71,10 +51,6 @@ pub const MSQRT_M1: FieldElement32 = FieldElement32([
     32595792,    7943725,  -9377950,  -3500415, -12389472,
     272473,     25146209,   2005654,   -326686, -11406482, ]);
 
-/// Precomputed value of 1/2 (mod p).
-pub const HALF: FieldElement32 = FieldElement32([
-    10, 0, 0, 0, 0, 0, 0, 0, 0, -16777216, ]);
-
 /// In Montgomery form y² = x³+Ax²+x, Curve25519 has A=486662.
 pub const A: FieldElement32       = FieldElement32([
     486662, 0, 0, 0, 0, 0, 0, 0, 0, 0, ]);
@@ -82,24 +58,11 @@ pub const A: FieldElement32       = FieldElement32([
 /// `APLUS2_OVER_FOUR` is (A+2)/4. (This is used internally within the Montgomery ladder.)
 pub const APLUS2_OVER_FOUR: FieldElement32 = FieldElement32([121666, 0, 0, 0, 0, 0, 0, 0, 0, 0]);
 
-/// `SQRT_MINUS_A` is sqrt(-486662)
-// XXX I think that this was used in Adam's code for his elligator
-// implementation, but that should maybe be using sqrt(-486664)
-// instead...?  - hdevalence
-pub const SQRT_MINUS_A: FieldElement32 = FieldElement32([ // sqrtMinusA
-    12222970,    8312128,  11511410,  -9067497,  15300785,
-    241793,    -25456130, -14121551,  12187136,  -3972024, ]);
-
 /// `SQRT_MINUS_APLUS2` is sqrt(-486664)
 pub const SQRT_MINUS_APLUS2: FieldElement32 = FieldElement32([
     -12222970, -8312128, -11511410, 9067497, -15300785,
     -241793, 25456130, 14121551, -12187136, 3972024]);
 
-/// `SQRT_MINUS_HALF` is sqrt(-1/2)
-pub const SQRT_MINUS_HALF: FieldElement32 = FieldElement32([ // sqrtMinusHalf
-    -17256545,   3971863,  28865457,  -1750208,  27359696,
-    -16640980,  12573105,   1002827,   -163343,  11073975, ]);
-
 /// Basepoint has y = 4/5.  This is called `_POINT` to distinguish it from `_TABLE`, which should
 /// be used for scalar multiplication (it's much faster).
 pub const ED25519_BASEPOINT_POINT: ExtendedPoint = ExtendedPoint{
diff --git a/src/constants_64bit.rs b/src/constants_64bit.rs
index f497b0d..bf03063 100644
--- a/src/constants_64bit.rs
+++ b/src/constants_64bit.rs
@@ -23,16 +23,10 @@ use edwards::ExtendedPoint;
 use edwards::AffineNielsPoint;
 use edwards::EdwardsBasepointTable;
 
-pub const p: FieldElement64 = FieldElement64([2251799813685229, 2251799813685247, 2251799813685247, 2251799813685247, 2251799813685247]);
-
 pub const d: FieldElement64 = FieldElement64([929955233495203, 466365720129213, 1662059464998953, 2033849074728123, 1442794654840575]);
 
 pub const d2: FieldElement64 = FieldElement64([1859910466990425, 932731440258426, 1072319116312658, 1815898335770999, 633789495995903]);
 
-pub const d4: FieldElement64 = FieldElement64([1468021120295602, 1865462880516853, 2144638232625316, 1379996857856750, 1267578991991807]);
-
-pub const a_minus_d: FieldElement64 = FieldElement64([1321844580190025, 1785434093556034, 589740348686294, 217950738957124, 809005158844672]);
-
 pub const sqrt_ad_minus_one: FieldElement64 = FieldElement64([
     2241493124984347, 425987919032274, 2207028919301688, 1220490630685848, 974799131293748
 ]);
@@ -41,10 +35,6 @@ pub const invsqrt_a_minus_d: FieldElement64 = FieldElement64([
     278908739862762, 821645201101625, 8113234426968, 1777959178193151, 2118520810568447
 ]);
 
-pub const inv_a_minus_d: FieldElement64 = FieldElement64([
-    2251799813563563, 2251799813685247, 2251799813685247, 2251799813685247, 2251799813685247
-]);
-
 /// Precomputed value of one of the square roots of -1 (mod p)
 pub const SQRT_M1: FieldElement64 = FieldElement64([1718705420411056, 234908883556509, 2233514472574048, 2117202627021982, 765476049583133]);
 
@@ -52,27 +42,15 @@ pub const SQRT_M1: FieldElement64 = FieldElement64([1718705420411056, 2349088835
 /// i.e., `MSQRT_M1 = -SQRT_M1`.
 pub const MSQRT_M1: FieldElement64 = FieldElement64([533094393274173, 2016890930128738, 18285341111199, 134597186663265, 1486323764102114]);
 
-/// Precomputed value of 1/2 (mod p).
-pub const HALF: FieldElement64 = FieldElement64([2251799813685239, 2251799813685247, 2251799813685247, 2251799813685247, 1125899906842623]);
-
 /// In Montgomery form y² = x³+Ax²+x, Curve25519 has A=486662.
 pub const A: FieldElement64 = FieldElement64([486662, 0, 0, 0, 0]);
 
 /// `APLUS2_OVER_FOUR` is (A+2)/4. (This is used internally within the Montgomery ladder.)
 pub const APLUS2_OVER_FOUR: FieldElement64 = FieldElement64([121666, 0, 0, 0, 0]);
 
-/// `SQRT_MINUS_A` is sqrt(-486662)
-// XXX I think that this was used in Adam's code for his elligator
-// implementation, but that should maybe be using sqrt(-486664)
-// instead...?  - hdevalence
-pub const SQRT_MINUS_A: FieldElement64 = FieldElement64([557817479725543, 1643290402203250, 16226468853936, 1304118542701054, 1985241807451647]);
-
 /// `SQRT_MINUS_APLUS2` is sqrt(-486664)
 pub const SQRT_MINUS_APLUS2: FieldElement64 = FieldElement64([1693982333959686, 608509411481997, 2235573344831311, 947681270984193, 266558006233600]);
 
-/// `SQRT_MINUS_HALF` is sqrt(-1/2)
-pub const SQRT_MINUS_HALF: FieldElement64 = FieldElement64([266547196637087, 2134345371906993, 1135042577398223, 67298593331632, 743161882051057]);
-
 /// Basepoint has y = 4/5.  This is called `_POINT` to distinguish it from `_TABLE`, which should
 /// be used for scalar multiplication (it's much faster).
 pub const ED25519_BASEPOINT_POINT: ExtendedPoint = ExtendedPoint{