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comparison bn_mp_mul_d.c @ 282:91fbc376f010 libtommath-orig libtommath-0.35

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Import of libtommath 0.35 From ltm-0.35.tar.bz2 SHA1 of 3f193dbae9351e92d02530994fa18236f7fde01c
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:16:18 +0000
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children 97db060d0ef5
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-1:000000000000 282:91fbc376f010
1 #include <tommath.h>
2 #ifdef BN_MP_MUL_D_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 *
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://math.libtomcrypt.org
16 */
17
18 /* multiply by a digit */
19 int
20 mp_mul_d (mp_int * a, mp_digit b, mp_int * c)
21 {
22 mp_digit u, *tmpa, *tmpc;
23 mp_word r;
24 int ix, res, olduse;
25
26 /* make sure c is big enough to hold a*b */
27 if (c->alloc < a->used + 1) {
28 if ((res = mp_grow (c, a->used + 1)) != MP_OKAY) {
29 return res;
30 }
31 }
32
33 /* get the original destinations used count */
34 olduse = c->used;
35
36 /* set the sign */
37 c->sign = a->sign;
38
39 /* alias for a->dp [source] */
40 tmpa = a->dp;
41
42 /* alias for c->dp [dest] */
43 tmpc = c->dp;
44
45 /* zero carry */
46 u = 0;
47
48 /* compute columns */
49 for (ix = 0; ix < a->used; ix++) {
50 /* compute product and carry sum for this term */
51 r = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b);
52
53 /* mask off higher bits to get a single digit */
54 *tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK));
55
56 /* send carry into next iteration */
57 u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
58 }
59
60 /* store final carry [if any] and increment ix offset */
61 *tmpc++ = u;
62 ++ix;
63
64 /* now zero digits above the top */
65 while (ix++ < olduse) {
66 *tmpc++ = 0;
67 }
68
69 /* set used count */
70 c->used = a->used + 1;
71 mp_clamp(c);
72
73 return MP_OKAY;
74 }
75 #endif