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Adjust BN_mod_inverse algorithm selection according to experiments on

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Ultra-Sparcs (both 32-bit and 64-bit compilations)
This commit is contained in:
Bodo Möller 2001-04-09 09:28:24 +00:00
parent 4d231b4359
commit 1f224bf029
2 changed files with 9 additions and 5 deletions
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9
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@ -6,9 +6,12 @@
*) Implement binary inversion algorithm for BN_mod_inverse in addition
to the algorithm using long divison. The binary algorithm can be
used only if the modulus is odd. It is faster only for relatively
small moduli (roughly 20% for 128-bit moduli, roughly 5% for 256-bit
moduli), so we use it only for moduli up to 400 bits.
used only if the modulus is odd. On 32-bit systems, it is faster
only for relatively small moduli (roughly 20-30% for 128-bit moduli,
roughly 5-15% for 256-bit moduli), so we use it only for moduli
up to 450 bits. In 64-bit environments, the binary algorithm
appears to be advantageous for much longer moduli; here we use it
for moduli up to 2048 bits.
[Bodo Moeller]
*) Change bctest again: '-x' expressions are not available in all

5
crypto/bn/bn_gcd.c
View File

@ -244,11 +244,12 @@ BIGNUM *BN_mod_inverse(BIGNUM *in,
* sign*Y*a == A (mod |n|).
*/
if (BN_is_odd(n) && (BN_num_bits(n) <= 400))
if (BN_is_odd(n) && (BN_num_bits(n) <= (BN_BITS <= 32 ? 450 : 2048)))
{
/* Binary inversion algorithm; requires odd modulus.
* This is faster than the general algorithm if the modulus
* is sufficiently small. */
* is sufficiently small (about 400 .. 500 bits on 32-bit
* sytems, but much more on 64-bit systems) */
int shift;
while (!BN_is_zero(B))