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Remove fixme notes from FieldElement code

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Henry de Valence 2018-07-16 22:11:48 -07:00
parent 8d46eacd2c
commit bc731f9d79
1 changed files with 5 additions and 16 deletions
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21
src/field.rs
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@ -96,17 +96,10 @@ impl FieldElement {
/// Compute (self^(2^250-1), self^11), used as a helper function /// Compute (self^(2^250-1), self^11), used as a helper function
/// within invert() and pow22523(). /// within invert() and pow22523().
///
/// XXX This returns an extra intermediate to save computation in
/// finding inverses, at the cost of an extra copy when it's not
/// used (e.g., when raising to (p-1)/2 or (p-5)/8). Good idea?
fn pow22501(&self) -> (FieldElement, FieldElement) { fn pow22501(&self) -> (FieldElement, FieldElement) {
// Instead of managing which temporary variables are used // Instead of managing which temporary variables are used
// for what, we define as many as we need and trust the // for what, we define as many as we need and leave stack
// compiler to reuse stack space as appropriate. // allocation to the compiler
//
// XXX testing some examples suggests that this does happen,
// but it would be good to check asm for this function.
// //
// Each temporary variable t_i is of the form (self)^e_i. // Each temporary variable t_i is of the form (self)^e_i.
// Squaring t_i corresponds to multiplying e_i by 2, // Squaring t_i corresponds to multiplying e_i by 2,
@ -177,12 +170,9 @@ impl FieldElement {
/// ///
/// The inverse is computed as self^(p-2), since /// The inverse is computed as self^(p-2), since
/// x^(p-2)x = x^(p-1) = 1 (mod p). /// x^(p-2)x = x^(p-1) = 1 (mod p).
// ///
// XXX do we want the debug assertion to check for zero? it breaks behaviour /// This function returns zero on input zero.
// such as that such as in curve25519_dalek::montgomery::test::identity_to_monty.
pub fn invert(&self) -> FieldElement { pub fn invert(&self) -> FieldElement {
// debug_assert!(*self != FieldElement::zero());
// The bits of p-2 = 2^255 -19 -2 are 11010111111...11. // The bits of p-2 = 2^255 -19 -2 are 11010111111...11.
// //
// nonzero bits of exponent // nonzero bits of exponent
@ -194,8 +184,7 @@ impl FieldElement {
} }
/// Raise this field element to the power (p-5)/8 = 2^252 -3. /// Raise this field element to the power (p-5)/8 = 2^252 -3.
/// Used in decoding. fn pow_p58(&self) -> FieldElement {
pub fn pow_p58(&self) -> FieldElement {
// The bits of (p-5)/8 are 101111.....11. // The bits of (p-5)/8 are 101111.....11.
// //
// nonzero bits of exponent // nonzero bits of exponent