Commit 263c44473896597346bc244d82a2b436d7d2da02 | zig | Meg's Mirrors

author	Frank Denis <124872+jedisct1@users.noreply.github.com> 2020-08-15 08:55:48+02:00
committer	Andrew Kelley <andrew@ziglang.org> 2020-08-16 22:35:27-07:00
log	263c44473896597346bc244d82a2b436d7d2da02
tree	fd6989ebe7fb7c753ea6f3ccaacbac329198753d
parent	ed558bfbaa737b187d894eddb8573cde15a3fb33

Move loop decrements into continuations

Suggested by @daurnimator

3 files changed, 3 insertions(+), 6 deletions(-)

lib
- std
  - crypto
    25519
    curve25519.zig
    edwards25519.zig
    scalar.zig

lib/std/crypto/25519/curve25519.zig+1-2

...	...	@@ -44,7 +44,7 @@ pub const Curve25519 = struct {
44	44	var z3 = Fe.one;
45	45	var swap: u8 = 0;
46	46	var pos: usize = bits - 1;
47		while (true) {
	47	while (true) : (pos -= 1) {
48	48	const b = (s[pos / 8] >> @intCast(u3, pos & 7)) & 1;
49	49	swap ^= b;
50	50	Fe.cSwap2(&x2, &x3, &z2, &z3, swap);
...	...	@@ -68,7 +68,6 @@ pub const Curve25519 = struct {
68	68	z3 = x1.mul(z2);
69	69	z2 = tmp1.mul(tmp0);
70	70	if (pos == 0) break;
71		pos -= 1;
72	71	}
73	72	Fe.cSwap2(&x2, &x3, &z2, &z3, swap);
74	73	z2 = z2.invert();

lib/std/crypto/25519/edwards25519.zig+1-2

...	...	@@ -132,12 +132,11 @@ pub const Edwards25519 = struct {
132	132	fn pcMul(pc: [16]Edwards25519, s: [32]u8) !Edwards25519 {
133	133	var q = Edwards25519.identityElement();
134	134	var pos: usize = 252;
135		while (true) {
	135	while (true) : (pos -= 4) {
136	136	q = q.dbl().dbl().dbl().dbl();
137	137	const b = (s[pos / 8] >> @intCast(u3, pos & 7)) & 0xf;
138	138	q = q.add(pcSelect(pc, b));
139	139	if (pos == 0) break;
140		pos -= 4;
141	140	}
142	141	try q.rejectIdentity();
143	142	return q;

lib/std/crypto/25519/scalar.zig+1-2

...	...	@@ -116,13 +116,12 @@ pub fn rejectNonCanonical(s: [32]u8) !void {
116	116	var c: u8 = 0;
117	117	var n: u8 = 1;
118	118	var i: usize = 31;
119		while (true) {
	119	while (true) : (i -= 1) {
120	120	const xs = @as(u16, s[i]);
121	121	const xfield_size = @as(u16, field_size[i]);
122	122	c \|= @intCast(u8, ((xs -% xfield_size) >> 8) & n);
123	123	n &= @intCast(u8, ((xs ^ xfield_size) -% 1) >> 8);
124	124	if (i == 0) break;
125		i -= 1;
126	125	}
127	126	if (c == 0) {
128	127	return error.NonCanonical;