8514b4166
Denys Vlasenko
2021-11-28
Subject
tls: P256: enable 64-bit version of montgomery reduction
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networking/tls_sp_c32.c+8 -7
| @@ -711,12 +711,13 @@ static void sp_512to256_mont_shift_8(sp_digit* r, sp_digit* a) | |
| memcpy(r, a + 8, sizeof(*r) * 8); | |
| } | |
| - | // Disabled for now. Seems to work, but ugly and 40 bytes larger on x86-64. |
| - | #if 0 //UNALIGNED_LE_64BIT |
| + | #if UNALIGNED_LE_64BIT |
| /* 64-bit little-endian optimized version. | |
| * See generic 32-bit version below for explanation. | |
| * The benefit of this version is: even though r[3] calculation is atrocious, | |
| * we call sp_256_mul_add_4() four times, not 8. | |
| + | * Measured run time improvement of curve_P256_compute_pubkey_and_premaster() |
| + | * call on x86-64: from ~1500us to ~900us. Code size +32 bytes. |
| */ | |
| static int sp_256_mul_add_4(uint64_t *r /*, const uint64_t* a, uint64_t b*/) | |
| { | |
| @@ -794,18 +795,18 @@ static int sp_256_mul_add_4(uint64_t *r /*, const uint64_t* a, uint64_t b*/) | |
| t64u = (t64 < b); | |
| t64 += r[3]; | |
| t64u += (t64 < r[3]); | |
| - | { |
| - | uint64_t lo,hi; |
| + | { // add ((((uint128_t)b << 32) - b) << 32): |
| + | uint64_t lo, hi; |
| //lo = (((b << 32) - b) << 32 | |
| //hi = (((uint128_t)b << 32) - b) >> 32 | |
| //but without uint128_t: | |
| - | hi = (b << 32) - b; /* form lower 32 bits of "hi" part 1 */ |
| + | hi = (b << 32) - b; /* make lower 32 bits of "hi", part 1 */ |
| b = (b >> 32) - (/*borrowed above?*/(b << 32) < b); /* upper 32 bits of "hi" are in b */ | |
| lo = hi << 32; /* (use "hi" value to calculate "lo",... */ | |
| t64 += lo; /* ...consume... */ | |
| t64u += (t64 < lo); /* ..."lo") */ | |
| - | hi >>= 32; /* form lower 32 bits of "hi" part 2 */ |
| - | hi |= (b << 32); /* combine lower and upper */ |
| + | hi >>= 32; /* make lower 32 bits of "hi", part 2 */ |
| + | hi |= (b << 32); /* combine lower and upper 32 bits */ |
| t64u += hi; /* consume "hi" */ | |
| } | |
| //t_hi = (t < m); | |