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Document RSAZ slightly better.

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Better commit such details to comments before I forget them.

Change-Id: Ie36332235c692f4369413b4340a742b5ad895ce1
Reviewed-on: https://boringssl-review.googlesource.com/25984
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
This commit is contained in:
David Benjamin 2018-02-13 20:47:28 -05:00 committed by CQ bot account: commit-bot@chromium.org
parent c03ecb93a2
commit 78a832d793
1 changed files with 13 additions and 6 deletions
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19
crypto/fipsmodule/bn/rsaz_exp.c
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@ -33,9 +33,12 @@ void rsaz_1024_scatter5_avx2(void *tbl, const void *val, int i);
void rsaz_1024_gather5_avx2(void *val, const void *tbl, int i);
void rsaz_1024_red2norm_avx2(void *norm, const void *red);
// one is 1 in RSAZ's representation.
alignas(64) static const BN_ULONG one[40] = {
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
// two80 is 2^80 in RSAZ's representation. Note RSAZ uses base 2^29, so this is
// 2^(29*2 + 22) = 2^80, not 2^(64*2 + 22).
alignas(64) static const BN_ULONG two80[40] = {
0, 0, 1 << 22, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
@ -60,8 +63,12 @@ void RSAZ_1024_mod_exp_avx2(BN_ULONG result_norm[16],
rsaz_1024_norm2red_avx2(a_inv, base_norm);
rsaz_1024_norm2red_avx2(R2, RR);
// Convert |R2| from the usual radix, giving R = 2^1024, to RSAZ's radix,
// giving R = 2^(36*29) = 2^1044.
rsaz_1024_mul_avx2(R2, R2, R2, m, k0);
// R2 = 2^2048 * 2^2048 / 2^1044 = 2^3052
rsaz_1024_mul_avx2(R2, R2, two80, m, k0);
// R2 = 2^3052 * 2^80 / 2^1044 = 2^2088 = (2^1044)^2
// table[0] = 1
rsaz_1024_mul_avx2(result, R2, one, m, k0);
@ -75,7 +82,7 @@ void RSAZ_1024_mod_exp_avx2(BN_ULONG result_norm[16],
rsaz_1024_sqr_avx2(result, a_inv, m, k0, 1);
rsaz_1024_scatter5_avx2(table_s, result, 2);
#if 0
// this is almost 2x smaller and less than 1% slower
// This is almost 2x smaller and less than 1% slower.
for (int index = 3; index < 32; index++) {
rsaz_1024_mul_avx2(result, result, a_inv, m, k0);
rsaz_1024_scatter5_avx2(table_s, result, index);
@ -191,7 +198,7 @@ void RSAZ_1024_mod_exp_avx2(BN_ULONG result_norm[16],
rsaz_1024_gather5_avx2(result, table_s, wvalue);
int index = 1014;
while (index > -1) { // loop for the remaining 127 windows
while (index > -1) { // Loop for the remaining 127 windows.
rsaz_1024_sqr_avx2(result, result, m, k0, 5);
@ -201,19 +208,19 @@ void RSAZ_1024_mod_exp_avx2(BN_ULONG result_norm[16],
wvalue = (wvalue >> (index % 8)) & 31;
index -= 5;
rsaz_1024_gather5_avx2(a_inv, table_s, wvalue); // borrow a_inv
rsaz_1024_gather5_avx2(a_inv, table_s, wvalue); // Borrow |a_inv|.
rsaz_1024_mul_avx2(result, result, a_inv, m, k0);
}
// square four times
// Square four times.
rsaz_1024_sqr_avx2(result, result, m, k0, 4);
wvalue = p_str[0] & 15;
rsaz_1024_gather5_avx2(a_inv, table_s, wvalue); // borrow a_inv
rsaz_1024_gather5_avx2(a_inv, table_s, wvalue); // Borrow |a_inv|.
rsaz_1024_mul_avx2(result, result, a_inv, m, k0);
// from Montgomery
// Convert from Montgomery.
rsaz_1024_mul_avx2(result, result, one, m, k0);
rsaz_1024_red2norm_avx2(result_norm, result);