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comparison tomsfastmath/src/bit/fp_mod_2d.c @ 643:a362b62d38b2 dropbear-tfm

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Add tomsfastmath from git rev bfa4582842bc3bab42e4be4aed5703437049502a with Makefile.in renamed
author Matt Johnston <matt@ucc.asn.au>
date Wed, 23 Nov 2011 18:10:20 +0700
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642:33fd2f3499d2 643:a362b62d38b2
1 /* TomsFastMath, a fast ISO C bignum library.
2 *
3 * This project is meant to fill in where LibTomMath
4 * falls short. That is speed ;-)
5 *
6 * This project is public domain and free for all purposes.
7 *
8 * Tom St Denis, [email protected]
9 */
10 #include <tfm.h>
11
12 /* c = a mod 2**d */
13 void fp_mod_2d(fp_int *a, int b, fp_int *c)
14 {
15 int x;
16
17 /* zero if count less than or equal to zero */
18 if (b <= 0) {
19 fp_zero(c);
20 return;
21 }
22
23 /* get copy of input */
24 fp_copy(a, c);
25
26 /* if 2**d is larger than we just return */
27 if (b >= (DIGIT_BIT * a->used)) {
28 return;
29 }
30
31 /* zero digits above the last digit of the modulus */
32 for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
33 c->dp[x] = 0;
34 }
35 /* clear the digit that is not completely outside/inside the modulus */
36 c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) >> (DIGIT_BIT - b);
37 fp_clamp (c);
38 }
39
40 /* $Source$ */
41 /* $Revision$ */
42 /* $Date$ */