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comparison bn_fast_s_mp_mul_digs.c @ 190:d8254fc979e9 libtommath-orig LTM_0.35

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Initial import of libtommath 0.35
author Matt Johnston <matt@ucc.asn.au>
date Fri, 06 May 2005 08:59:30 +0000
parents d29b64170cf0
children
comparison
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142:d29b64170cf0 190:d8254fc979e9
29 * required for fast Barrett reduction). 29 * required for fast Barrett reduction).
30 * 30 *
31 * Based on Algorithm 14.12 on pp.595 of HAC. 31 * Based on Algorithm 14.12 on pp.595 of HAC.
32 * 32 *
33 */ 33 */
34 int 34 int fast_s_mp_mul_digs (mp_int * a, mp_int * b, mp_int * c, int digs)
35 fast_s_mp_mul_digs (mp_int * a, mp_int * b, mp_int * c, int digs)
36 { 35 {
37 int olduse, res, pa, ix, iz; 36 int olduse, res, pa, ix, iz;
38 mp_digit W[MP_WARRAY]; 37 mp_digit W[MP_WARRAY];
39 register mp_word _W; 38 register mp_word _W;
40 39
48 /* number of output digits to produce */ 47 /* number of output digits to produce */
49 pa = MIN(digs, a->used + b->used); 48 pa = MIN(digs, a->used + b->used);
50 49
51 /* clear the carry */ 50 /* clear the carry */
52 _W = 0; 51 _W = 0;
53 for (ix = 0; ix <= pa; ix++) { 52 for (ix = 0; ix < pa; ix++) {
54 int tx, ty; 53 int tx, ty;
55 int iy; 54 int iy;
56 mp_digit *tmpx, *tmpy; 55 mp_digit *tmpx, *tmpy;
57 56
58 /* get offsets into the two bignums */ 57 /* get offsets into the two bignums */
61 60
62 /* setup temp aliases */ 61 /* setup temp aliases */
63 tmpx = a->dp + tx; 62 tmpx = a->dp + tx;
64 tmpy = b->dp + ty; 63 tmpy = b->dp + ty;
65 64
66 /* this is the number of times the loop will iterrate, essentially its 65 /* this is the number of times the loop will iterrate, essentially
67 while (tx++ < a->used && ty-- >= 0) { ... } 66 while (tx++ < a->used && ty-- >= 0) { ... }
68 */ 67 */
69 iy = MIN(a->used-tx, ty+1); 68 iy = MIN(a->used-tx, ty+1);
70 69
71 /* execute loop */ 70 /* execute loop */
78 77
79 /* make next carry */ 78 /* make next carry */
80 _W = _W >> ((mp_word)DIGIT_BIT); 79 _W = _W >> ((mp_word)DIGIT_BIT);
81 } 80 }
82 81
82 /* store final carry */
83 W[ix] = (mp_digit)(_W & MP_MASK);
84
83 /* setup dest */ 85 /* setup dest */
84 olduse = c->used; 86 olduse = c->used;
85 c->used = digs; 87 c->used = pa;
86 88
87 { 89 {
88 register mp_digit *tmpc; 90 register mp_digit *tmpc;
89 tmpc = c->dp; 91 tmpc = c->dp;
90 for (ix = 0; ix < digs; ix++) { 92 for (ix = 0; ix < pa+1; ix++) {
91 /* now extract the previous digit [below the carry] */ 93 /* now extract the previous digit [below the carry] */
92 *tmpc++ = W[ix]; 94 *tmpc++ = W[ix];
93 } 95 }
94 96
95 /* clear unused digits [that existed in the old copy of c] */ 97 /* clear unused digits [that existed in the old copy of c] */