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fix modp256k1_shift

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NIIBE Yutaka
2014-02-21 11:36:15 +09:00
parent 9feeeb308b
commit 2accc339e2
2 changed files with 15 additions and 16 deletions
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4
ChangeLog
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@@ -1,3 +1,7 @@
2014-02-21 Niibe Yutaka <gniibe@fsij.org>
* src/modp256k1.c (modp256k1_shift): Bug fix.
2014-02-20 Niibe Yutaka <gniibe@fsij.org>
* src/Makefile.in (CSRC): Add files of p256k1.

27
src/modp256k1.c
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@@ -463,7 +463,6 @@ void
modp256k1_shift (bn256 *X, const bn256 *A, int shift)
{
uint32_t carry;
#define borrow carry
bn256 tmp[1];
carry = bn256_shift (X, A, shift);
@@ -471,20 +470,16 @@ modp256k1_shift (bn256 *X, const bn256 *A, int shift)
return;
memset (tmp, 0, sizeof (bn256));
tmp->word[7] = carry;
tmp->word[0] = carry;
tmp->word[0] = carry + (carry << 9);
tmp->word[1] = carry + (tmp->word[0] < (carry << 9)) + (carry >> 23);
tmp->word[0] = tmp->word[0] + (carry << 8);
tmp->word[1] = tmp->word[1] + (tmp->word[0] < (carry << 8)) + (carry >> 24);
tmp->word[0] = tmp->word[0] + (carry << 7);
tmp->word[1] = tmp->word[1] + (tmp->word[0] < (carry << 7)) + (carry >> 25);
tmp->word[0] = tmp->word[0] + (carry << 6);
tmp->word[1] = tmp->word[1] + (tmp->word[0] < (carry << 6)) + (carry >> 26);
tmp->word[0] = tmp->word[0] + (carry << 4);
tmp->word[1] = tmp->word[1] + (tmp->word[0] < (carry << 4)) + (carry >> 28);
modp256k1_add (X, X, tmp);
tmp->word[7] = 0;
tmp->word[0] = 0;
tmp->word[6] = carry;
tmp->word[3] = carry;
modp256k1_sub (X, X, tmp);
borrow = bn256_sub (tmp, X, P256K1);
if (borrow)
memcpy (tmp, X, sizeof (bn256));
else
memcpy (X, tmp, sizeof (bn256));
#undef borrow
}