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comparison bn_mp_exptmod.c @ 142:d29b64170cf0 libtommath-orig

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import of libtommath 0.32
author Matt Johnston <matt@ucc.asn.au>
date Sun, 19 Dec 2004 11:33:56 +0000
parents 86e0b50a9b58
children a96ff234ff19 d8254fc979e9
comparison
equal deleted inserted replaced
19:e1037a1e12e7 142:d29b64170cf0
1 #include <tommath.h>
2 #ifdef BN_MP_EXPTMOD_C
1 /* LibTomMath, multiple-precision integer library -- Tom St Denis 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
2 * 4 *
3 * LibTomMath is a library that provides multiple-precision 5 * LibTomMath is a library that provides multiple-precision
4 * integer arithmetic as well as number theoretic functionality. 6 * integer arithmetic as well as number theoretic functionality.
5 * 7 *
10 * The library is free for all purposes without any express 12 * The library is free for all purposes without any express
11 * guarantee it works. 13 * guarantee it works.
12 * 14 *
13 * Tom St Denis, [email protected], http://math.libtomcrypt.org 15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
14 */ 16 */
15 #include <tommath.h>
16 17
17 18
18 /* this is a shell function that calls either the normal or Montgomery 19 /* this is a shell function that calls either the normal or Montgomery
19 * exptmod functions. Originally the call to the montgomery code was 20 * exptmod functions. Originally the call to the montgomery code was
20 * embedded in the normal function but that wasted alot of stack space 21 * embedded in the normal function but that wasted alot of stack space
29 return MP_VAL; 30 return MP_VAL;
30 } 31 }
31 32
32 /* if exponent X is negative we have to recurse */ 33 /* if exponent X is negative we have to recurse */
33 if (X->sign == MP_NEG) { 34 if (X->sign == MP_NEG) {
35 #ifdef BN_MP_INVMOD_C
34 mp_int tmpG, tmpX; 36 mp_int tmpG, tmpX;
35 int err; 37 int err;
36 38
37 /* first compute 1/G mod P */ 39 /* first compute 1/G mod P */
38 if ((err = mp_init(&tmpG)) != MP_OKAY) { 40 if ((err = mp_init(&tmpG)) != MP_OKAY) {
55 57
56 /* and now compute (1/G)**|X| instead of G**X [X < 0] */ 58 /* and now compute (1/G)**|X| instead of G**X [X < 0] */
57 err = mp_exptmod(&tmpG, &tmpX, P, Y); 59 err = mp_exptmod(&tmpG, &tmpX, P, Y);
58 mp_clear_multi(&tmpG, &tmpX, NULL); 60 mp_clear_multi(&tmpG, &tmpX, NULL);
59 return err; 61 return err;
62 #else
63 /* no invmod */
64 return MP_VAL
65 #endif
60 } 66 }
61 67
68 #ifdef BN_MP_DR_IS_MODULUS_C
62 /* is it a DR modulus? */ 69 /* is it a DR modulus? */
63 dr = mp_dr_is_modulus(P); 70 dr = mp_dr_is_modulus(P);
71 #else
72 dr = 0;
73 #endif
64 74
75 #ifdef BN_MP_REDUCE_IS_2K_C
65 /* if not, is it a uDR modulus? */ 76 /* if not, is it a uDR modulus? */
66 if (dr == 0) { 77 if (dr == 0) {
67 dr = mp_reduce_is_2k(P) << 1; 78 dr = mp_reduce_is_2k(P) << 1;
68 } 79 }
80 #endif
69 81
70 /* if the modulus is odd or dr != 0 use the fast method */ 82 /* if the modulus is odd or dr != 0 use the fast method */
83 #ifdef BN_MP_EXPTMOD_FAST_C
71 if (mp_isodd (P) == 1 || dr != 0) { 84 if (mp_isodd (P) == 1 || dr != 0) {
72 return mp_exptmod_fast (G, X, P, Y, dr); 85 return mp_exptmod_fast (G, X, P, Y, dr);
73 } else { 86 } else {
87 #endif
88 #ifdef BN_S_MP_EXPTMOD_C
74 /* otherwise use the generic Barrett reduction technique */ 89 /* otherwise use the generic Barrett reduction technique */
75 return s_mp_exptmod (G, X, P, Y); 90 return s_mp_exptmod (G, X, P, Y);
91 #else
92 /* no exptmod for evens */
93 return MP_VAL;
94 #endif
95 #ifdef BN_MP_EXPTMOD_FAST_C
76 } 96 }
97 #endif
77 } 98 }
78 99
100 #endif