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comparison libtommath/bn_mp_dr_reduce.c @ 1436:60fc6476e044

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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
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1435:f849a5ca2efc 1436:60fc6476e044
1 #include <tommath.h> 1 #include <tommath_private.h>
2 #ifdef BN_MP_DR_REDUCE_C 2 #ifdef BN_MP_DR_REDUCE_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 /* reduce "x" in place modulo "n" using the Diminished Radix algorithm. 18 /* reduce "x" in place modulo "n" using the Diminished Radix algorithm.
19 * 19 *
20 * Based on algorithm from the paper 20 * Based on algorithm from the paper
38 38
39 /* m = digits in modulus */ 39 /* m = digits in modulus */
40 m = n->used; 40 m = n->used;
41 41
42 /* ensure that "x" has at least 2m digits */ 42 /* ensure that "x" has at least 2m digits */
43 if (x->alloc < m + m) { 43 if (x->alloc < (m + m)) {
44 if ((err = mp_grow (x, m + m)) != MP_OKAY) { 44 if ((err = mp_grow (x, m + m)) != MP_OKAY) {
45 return err; 45 return err;
46 } 46 }
47 } 47 }
48 48
60 /* set carry to zero */ 60 /* set carry to zero */
61 mu = 0; 61 mu = 0;
62 62
63 /* compute (x mod B**m) + k * [x/B**m] inline and inplace */ 63 /* compute (x mod B**m) + k * [x/B**m] inline and inplace */
64 for (i = 0; i < m; i++) { 64 for (i = 0; i < m; i++) {
65 r = ((mp_word)*tmpx2++) * ((mp_word)k) + *tmpx1 + mu; 65 r = (((mp_word)*tmpx2++) * (mp_word)k) + *tmpx1 + mu;
66 *tmpx1++ = (mp_digit)(r & MP_MASK); 66 *tmpx1++ = (mp_digit)(r & MP_MASK);
67 mu = (mp_digit)(r >> ((mp_word)DIGIT_BIT)); 67 mu = (mp_digit)(r >> ((mp_word)DIGIT_BIT));
68 } 68 }
69 69
70 /* set final carry */ 70 /* set final carry */
80 80
81 /* if x >= n then subtract and reduce again 81 /* if x >= n then subtract and reduce again
82 * Each successive "recursion" makes the input smaller and smaller. 82 * Each successive "recursion" makes the input smaller and smaller.
83 */ 83 */
84 if (mp_cmp_mag (x, n) != MP_LT) { 84 if (mp_cmp_mag (x, n) != MP_LT) {
85 s_mp_sub(x, n, x); 85 if ((err = s_mp_sub(x, n, x)) != MP_OKAY) {
86 return err;
87 }
86 goto top; 88 goto top;
87 } 89 }
88 return MP_OKAY; 90 return MP_OKAY;
89 } 91 }
90 #endif 92 #endif
91 93
92 /* $Source: /cvs/libtom/libtommath/bn_mp_dr_reduce.c,v $ */ 94 /* $Source$ */
93 /* $Revision: 1.3 $ */ 95 /* $Revision$ */
94 /* $Date: 2006/03/31 14:18:44 $ */ 96 /* $Date$ */