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crypto/pcurves: compute constants for inversion at comptime (#11780)

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Frank Denis 2022-06-13 08:13:52 +02:00 committed by GitHub
parent 13f02c30e6
commit 7c660d17cd
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1 changed files with 13 additions and 9 deletions
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22
lib/std/crypto/pcurves/common.zig
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@ -203,19 +203,17 @@ pub fn Field(comptime params: FieldParams) type {
const XLimbs = [a.limbs.len + 1]Word; const XLimbs = [a.limbs.len + 1]Word;
var d: Word = 1; var d: Word = 1;
var f: XLimbs = undefined; var f = comptime blk: {
fiat.msat(&f); var f: XLimbs = undefined;
fiat.msat(&f);
break :blk f;
};
var g: XLimbs = undefined; var g: XLimbs = undefined;
fiat.fromMontgomery(g[0..a.limbs.len], a.limbs); fiat.fromMontgomery(g[0..a.limbs.len], a.limbs);
g[g.len - 1] = 0; g[g.len - 1] = 0;
var r: Limbs = undefined; var r = Fe.one.limbs;
fiat.setOne(&r); var v = Fe.zero.limbs;
var v = mem.zeroes(Limbs);
var precomp: Limbs = undefined;
fiat.divstepPrecomp(&precomp);
var out1: Word = undefined; var out1: Word = undefined;
var out2: XLimbs = undefined; var out2: XLimbs = undefined;
@ -236,6 +234,12 @@ pub fn Field(comptime params: FieldParams) type {
var v_opp: Limbs = undefined; var v_opp: Limbs = undefined;
fiat.opp(&v_opp, v); fiat.opp(&v_opp, v);
fiat.selectznz(&v, @truncate(u1, f[f.len - 1] >> (@bitSizeOf(Word) - 1)), v, v_opp); fiat.selectznz(&v, @truncate(u1, f[f.len - 1] >> (@bitSizeOf(Word) - 1)), v, v_opp);
const precomp = blk: {
var precomp: Limbs = undefined;
fiat.divstepPrecomp(&precomp);
break :blk precomp;
};
var fe: Fe = undefined; var fe: Fe = undefined;
fiat.mul(&fe.limbs, v, precomp); fiat.mul(&fe.limbs, v, precomp);
return fe; return fe;