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comparison libtommath/bn_s_mp_mul_digs.c @ 1739:13d834efc376 fuzz

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merge from main
author Matt Johnston <matt@ucc.asn.au>
date Thu, 15 Oct 2020 19:55:15 +0800
parents 1051e4eea25a
children
comparison
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1562:768ebf737aa0 1739:13d834efc376
1 #include <tommath_private.h> 1 #include "tommath_private.h"
2 #ifdef BN_S_MP_MUL_DIGS_C 2 #ifdef BN_S_MP_MUL_DIGS_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
4 * 4 /* SPDX-License-Identifier: Unlicense */
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
7 *
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
11 *
12 * The library is free for all purposes without any express
13 * guarantee it works.
14 *
15 * Tom St Denis, [email protected], http://libtom.org
16 */
17 5
18 /* multiplies |a| * |b| and only computes upto digs digits of result 6 /* multiplies |a| * |b| and only computes upto digs digits of result
19 * HAC pp. 595, Algorithm 14.12 Modified so you can control how 7 * HAC pp. 595, Algorithm 14.12 Modified so you can control how
20 * many digits of output are created. 8 * many digits of output are created.
21 */ 9 */
22 int s_mp_mul_digs (mp_int * a, mp_int * b, mp_int * c, int digs) 10 mp_err s_mp_mul_digs(const mp_int *a, const mp_int *b, mp_int *c, int digs)
23 { 11 {
24 mp_int t; 12 mp_int t;
25 int res, pa, pb, ix, iy; 13 mp_err err;
26 mp_digit u; 14 int pa, pb, ix, iy;
27 mp_word r; 15 mp_digit u;
28 mp_digit tmpx, *tmpt, *tmpy; 16 mp_word r;
17 mp_digit tmpx, *tmpt, *tmpy;
29 18
30 /* can we use the fast multiplier? */ 19 /* can we use the fast multiplier? */
31 if (((digs) < MP_WARRAY) && 20 if ((digs < MP_WARRAY) &&
32 (MIN (a->used, b->used) < 21 (MP_MIN(a->used, b->used) < MP_MAXFAST)) {
33 (1 << ((CHAR_BIT * sizeof(mp_word)) - (2 * DIGIT_BIT))))) { 22 return s_mp_mul_digs_fast(a, b, c, digs);
34 return fast_s_mp_mul_digs (a, b, c, digs); 23 }
35 }
36 24
37 if ((res = mp_init_size (&t, digs)) != MP_OKAY) { 25 if ((err = mp_init_size(&t, digs)) != MP_OKAY) {
38 return res; 26 return err;
39 } 27 }
40 t.used = digs; 28 t.used = digs;
41 29
42 /* compute the digits of the product directly */ 30 /* compute the digits of the product directly */
43 pa = a->used; 31 pa = a->used;
44 for (ix = 0; ix < pa; ix++) { 32 for (ix = 0; ix < pa; ix++) {
45 /* set the carry to zero */ 33 /* set the carry to zero */
46 u = 0; 34 u = 0;
47 35
48 /* limit ourselves to making digs digits of output */ 36 /* limit ourselves to making digs digits of output */
49 pb = MIN (b->used, digs - ix); 37 pb = MP_MIN(b->used, digs - ix);
50 38
51 /* setup some aliases */ 39 /* setup some aliases */
52 /* copy of the digit from a used within the nested loop */ 40 /* copy of the digit from a used within the nested loop */
53 tmpx = a->dp[ix]; 41 tmpx = a->dp[ix];
54
55 /* an alias for the destination shifted ix places */
56 tmpt = t.dp + ix;
57
58 /* an alias for the digits of b */
59 tmpy = b->dp;
60 42
61 /* compute the columns of the output and propagate the carry */ 43 /* an alias for the destination shifted ix places */
62 for (iy = 0; iy < pb; iy++) { 44 tmpt = t.dp + ix;
63 /* compute the column as a mp_word */
64 r = (mp_word)*tmpt +
65 ((mp_word)tmpx * (mp_word)*tmpy++) +
66 (mp_word)u;
67 45
68 /* the new column is the lower part of the result */ 46 /* an alias for the digits of b */
69 *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK)); 47 tmpy = b->dp;
70 48
71 /* get the carry word from the result */ 49 /* compute the columns of the output and propagate the carry */
72 u = (mp_digit) (r >> ((mp_word) DIGIT_BIT)); 50 for (iy = 0; iy < pb; iy++) {
73 } 51 /* compute the column as a mp_word */
74 /* set carry if it is placed below digs */ 52 r = (mp_word)*tmpt +
75 if ((ix + iy) < digs) { 53 ((mp_word)tmpx * (mp_word)*tmpy++) +
76 *tmpt = u; 54 (mp_word)u;
77 }
78 }
79 55
80 mp_clamp (&t); 56 /* the new column is the lower part of the result */
81 mp_exch (&t, c); 57 *tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);
82 58
83 mp_clear (&t); 59 /* get the carry word from the result */
84 return MP_OKAY; 60 u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
61 }
62 /* set carry if it is placed below digs */
63 if ((ix + iy) < digs) {
64 *tmpt = u;
65 }
66 }
67
68 mp_clamp(&t);
69 mp_exch(&t, c);
70
71 mp_clear(&t);
72 return MP_OKAY;
85 } 73 }
86 #endif 74 #endif
87
88 /* ref: $Format:%D$ */
89 /* git commit: $Format:%H$ */
90 /* commit time: $Format:%ai$ */