Mercurial > dropbear

comparison libtommath/bn_mp_montgomery_setup.c @ 1436:60fc6476e044

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Update to libtommath v1.0
author Matt Johnston <matt@ucc.asn.au>
date Sat, 24 Jun 2017 22:37:14 +0800
parents 5ff8218bcee9
children 8bba51a55704
comparison
equal deleted inserted replaced
1435:f849a5ca2efc 1436:60fc6476e044
1 #include <tommath.h> 1 #include <tommath_private.h>
2 #ifdef BN_MP_MONTGOMERY_SETUP_C 2 #ifdef BN_MP_MONTGOMERY_SETUP_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 * 4 *
5 * LibTomMath is a library that provides multiple-precision 5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality. 6 * integer arithmetic as well as number theoretic functionality.
10 * additional optimizations in place. 10 * additional optimizations in place.
11 * 11 *
12 * The library is free for all purposes without any express 12 * The library is free for all purposes without any express
13 * guarantee it works. 13 * guarantee it works.
14 * 14 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.com 15 * Tom St Denis, [email protected], http://libtom.org
16 */ 16 */
17 17
18 /* setups the montgomery reduction stuff */ 18 /* setups the montgomery reduction stuff */
19 int 19 int
20 mp_montgomery_setup (mp_int * n, mp_digit * rho) 20 mp_montgomery_setup (mp_int * n, mp_digit * rho)
34 if ((b & 1) == 0) { 34 if ((b & 1) == 0) {
35 return MP_VAL; 35 return MP_VAL;
36 } 36 }
37 37
38 x = (((b + 2) & 4) << 1) + b; /* here x*a==1 mod 2**4 */ 38 x = (((b + 2) & 4) << 1) + b; /* here x*a==1 mod 2**4 */
39 x *= 2 - b * x; /* here x*a==1 mod 2**8 */ 39 x *= 2 - (b * x); /* here x*a==1 mod 2**8 */
40 #if !defined(MP_8BIT) 40 #if !defined(MP_8BIT)
41 x *= 2 - b * x; /* here x*a==1 mod 2**16 */ 41 x *= 2 - (b * x); /* here x*a==1 mod 2**16 */
42 #endif 42 #endif
43 #if defined(MP_64BIT) || !(defined(MP_8BIT) || defined(MP_16BIT)) 43 #if defined(MP_64BIT) || !(defined(MP_8BIT) || defined(MP_16BIT))
44 x *= 2 - b * x; /* here x*a==1 mod 2**32 */ 44 x *= 2 - (b * x); /* here x*a==1 mod 2**32 */
45 #endif 45 #endif
46 #ifdef MP_64BIT 46 #ifdef MP_64BIT
47 x *= 2 - b * x; /* here x*a==1 mod 2**64 */ 47 x *= 2 - (b * x); /* here x*a==1 mod 2**64 */
48 #endif 48 #endif
49 49
50 /* rho = -1/m mod b */ 50 /* rho = -1/m mod b */
51 *rho = (unsigned long)(((mp_word)1 << ((mp_word) DIGIT_BIT)) - x) & MP_MASK; 51 *rho = (mp_digit)(((mp_word)1 << ((mp_word) DIGIT_BIT)) - x) & MP_MASK;
52 52
53 return MP_OKAY; 53 return MP_OKAY;
54 } 54 }
55 #endif 55 #endif
56 56
57 /* $Source: /cvs/libtom/libtommath/bn_mp_montgomery_setup.c,v $ */ 57 /* $Source$ */
58 /* $Revision: 1.4 $ */ 58 /* $Revision$ */
59 /* $Date: 2006/12/04 21:34:03 $ */ 59 /* $Date$ */