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Use the equivalent of a sliding window (without precomputation

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because we're only handling words anyway) in BN_mod_exp_mont_word
making it a little faster for very small exponents,
and adjust the performance gain estimate in CHANGES according
to slightly more thorough measurements.
(15% faster than BN_mod_exp_mont for "large" base,
20% faster than BN_mod_exp_mont for small base.)
This commit is contained in:
Bodo Möller 2000-06-08 09:39:28 +00:00
parent 6dad7bd69c
commit f8989a2155
2 changed files with 96 additions and 18 deletions
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5
CHANGES
View File

@ -4,9 +4,8 @@
Changes between 0.9.5a and 0.9.6 [xx XXX 2000]
*) New function BN_mod_exp_mont_word for small bases (roughly 20%
faster than BN_mod_exp_mont even though it does not use
windowing).
*) New function BN_mod_exp_mont_word for small bases (roughly 15-20%
faster than BN_mod_exp_mont).
[Bodo Moeller]
*) CygWin32 support.

109
crypto/bn/bn_exp.c
View File

@ -55,6 +55,60 @@
* copied and put under another distribution licence
* [including the GNU Public Licence.]
*/
/* ====================================================================
* Copyright (c) 1998-2000 The OpenSSL Project. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. All advertising materials mentioning features or use of this
* software must display the following acknowledgment:
* "This product includes software developed by the OpenSSL Project
* for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
*
* 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
* endorse or promote products derived from this software without
* prior written permission. For written permission, please contact
* openssl-core@openssl.org.
*
* 5. Products derived from this software may not be called "OpenSSL"
* nor may "OpenSSL" appear in their names without prior written
* permission of the OpenSSL Project.
*
* 6. Redistributions of any form whatsoever must retain the following
* acknowledgment:
* "This product includes software developed by the OpenSSL Project
* for use in the OpenSSL Toolkit (http://www.openssl.org/)"
*
* THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
* EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
* ====================================================================
*
* This product includes cryptographic software written by Eric Young
* (eay@cryptsoft.com). This product includes software written by Tim
* Hudson (tjh@cryptsoft.com).
*
*/
#include <stdio.h>
#include "cryptlib.h"
@ -611,11 +665,17 @@ err:
int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
/* if we had BN_mod_exp_mont_2, we could even use windowing in it */
{
int b, bits, ret=0;
BIGNUM *d, *r, *t;
BN_MONT_CTX *mont = NULL;
int b, bits, ret=0;
BN_ULONG w, next_w;
BIGNUM *d, *r, *t;
BIGNUM *swap_tmp;
#define BN_MOD_MUL_WORD(r, w, m) \
(BN_mul_word(r, (w)) && \
(BN_ucmp(r, (m)) >= 0 ? \
(BN_mod(t, r, m, ctx) && (swap_tmp = r, r = t, t = swap_tmp, 1)) : \
1))
bn_check_top(p);
bn_check_top(m);
@ -656,26 +716,45 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
}
if (!BN_to_montgomery(r, BN_value_one(), mont, ctx)) goto err;
for (b = bits-1; b >= 0; b--)
/* bits-1 >= 0 */
/* The result is accumulated in the product r*w. */
w = a; /* bit 'bits-1' of 'p' is always set */
for (b = bits-2; b >= 0; b--)
{
/* First, square r*w. */
next_w = w*w;
if ((next_w/w) != w) /* overflow */
{
if (!BN_MOD_MUL_WORD(r, w, m))
goto err;
next_w = 1;
}
w = next_w;
if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
goto err;
/* Second, multiply r*w by 'a' if exponent bit is set. */
if (BN_is_bit_set(p, b))
{
if (!BN_mul_word(r, a))
goto err;
if (BN_ucmp(r, m) >= 0)
next_w = w*a;
if ((next_w/a) != w) /* overflow */
{
if (!BN_mod(t, r, m, ctx))
if (!BN_MOD_MUL_WORD(r, w, m))
goto err;
{ BIGNUM *swap_tmp = r; r = t; t = swap_tmp; }
next_w = a;
}
}
if (b > 0)
{
if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
goto err;
w = next_w;
}
}
/* Finally, set r:=r*w. */
if (w != 1)
{
if (!BN_MOD_MUL_WORD(r, w, m))
goto err;
}
BN_from_montgomery(rr, r, mont, ctx);
ret = 1;
err: