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improve a bit

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NIIBE Yutaka
2014-03-26 18:37:38 +09:00
parent fc53d507ce
commit 1920c5fc69
3 changed files with 42 additions and 42 deletions
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7
ChangeLog
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@@ -1,3 +1,10 @@
2014-03-26 Niibe Yutaka <gniibe@fsij.org>
* src/mod25638.c (mod25638_reduce): New.
(mod25638_mul, mod25638_sqr): Use mod25638_reduce.
* src/ecc-edwards.c (ptc_to_ac_25519): No need to subtract p25519.
2014-03-25 Niibe Yutaka <gniibe@fsij.org>
* misc/t-eddsa.c: New.

15
src/ecc-edwards.c
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@@ -219,20 +219,9 @@ ptc_to_ac_25519 (ac *X, const ptc *A)
/*
* A->z may be bigger than p25519, or two times bigger than p25519.
* We try to subtract p25519 twice.
* But this is no problem for computation of mod_inv.
*/
borrow = bn256_sub (z_inv, A->z, p25519);
if (borrow)
memcpy (z_inv, A->z, sizeof (bn256));
else
memcpy (z, A->z, sizeof (bn256)); /* dumy copy */
borrow = bn256_sub (z, z_inv, p25519);
if (borrow)
memcpy (z, z_inv, sizeof (bn256));
else
memcpy (z_inv, z, sizeof (bn256)); /* dumy copy */
mod_inv (z_inv, z, p25519);
mod_inv (z_inv, A->z, p25519);
mod25638_mul (X->x, A->x, z_inv);
borrow = bn256_sub (z, X->x, p25519);

62
src/mod25638.c
View File

@@ -123,39 +123,29 @@ mod25638_sub (bn256 *X, const bn256 *A, const bn256 *B)
/**
* @brief X = (A * B) mod 2^256-38
* @brief X = A mod 25638
*
* Note that the second argument is not "const bn512 *".
* A is modified during the computation of modulo.
*/
void
mod25638_mul (bn256 *X, const bn256 *A, const bn256 *B)
static void
mod25638_reduce (bn256 *X, bn512 *A)
{
uint32_t word[BN256_WORDS*2];
const uint32_t *s;
uint32_t *d;
uint32_t w;
uint32_t c, c0;
#if ASM_IMPLEMENTATION
memset (word, 0, sizeof (uint32_t)*BN256_WORDS);
uint32_t c, c0;
s = A->word; d = &word[0]; w = B->word[0]; MULADD_256 (s, d, w, c);
s = A->word; d = &word[1]; w = B->word[1]; MULADD_256 (s, d, w, c);
s = A->word; d = &word[2]; w = B->word[2]; MULADD_256 (s, d, w, c);
s = A->word; d = &word[3]; w = B->word[3]; MULADD_256 (s, d, w, c);
s = A->word; d = &word[4]; w = B->word[4]; MULADD_256 (s, d, w, c);
s = A->word; d = &word[5]; w = B->word[5]; MULADD_256 (s, d, w, c);
s = A->word; d = &word[6]; w = B->word[6]; MULADD_256 (s, d, w, c);
s = A->word; d = &word[7]; w = B->word[7]; MULADD_256 (s, d, w, c);
s = &word[8]; d = &word[0]; w = 38; MULADD_256 (s, d, w, c);
c0 = word[8] * 38;
s = word;
s = &A->word[8]; d = &A->word[0]; w = 38; MULADD_256 (s, d, w, c);
c0 = A->word[8] * 38;
s = &A->word[0];
ADDWORD_256 (s, c0, c);
word[0] += c * 38;
memcpy (X, word, sizeof (bn256));
A->word[0] += c * 38;
memcpy (X, A, sizeof (bn256));
#else
(void)c; (void)c0;
bn256_mul ((bn512 *)word, A, B);
s = &word[8]; d = &word[0]; w = 38;
s = &A->word[8]; d = &A->word[0]; w = 38;
{
int i;
uint64_t r;
@@ -179,8 +169,8 @@ mod25638_mul (bn256 *X, const bn256 *A, const bn256 *B)
}
d[i] = (uint32_t)r;
r0 = word[8] * 38;
d = word;
r0 = A->word[8] * 38;
d = &A->word[0];
for (i = 0; i < BN256_WORDS; i++)
{
r0 += d[i];
@@ -188,21 +178,35 @@ mod25638_mul (bn256 *X, const bn256 *A, const bn256 *B)
d[i] = r0;
r0 = carry;
}
word[0] += r0 * 38;
A->word[0] += r0 * 38;
}
memcpy (X, word, sizeof (bn256));
memcpy (X, A, sizeof (bn256));
#endif
}
/**
* @brief X = (A * B) mod 2^256-38
*/
void
mod25638_mul (bn256 *X, const bn256 *A, const bn256 *B)
{
bn512 tmp[1];
bn256_mul (tmp, A, B);
mod25638_reduce (X, tmp);
}
/**
* @brief X = A * A mod 2^256-38
*/
void
mod25638_sqr (bn256 *X, const bn256 *A)
{
/* This could be improved a bit, see bn256_sqr. */
mod25638_mul (X, A, A);
bn512 tmp[1];
bn256_sqr (tmp, A);
mod25638_reduce (X, tmp);
}