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, tomstdenis@gmail.com
9  */
10 #include "bignum_fast.h"
11 
12 /* c = a mod 2**d */
fp_mod_2d(fp_int * a,int b,fp_int * c)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: /cvs/libtom/tomsfastmath/src/bit/fp_mod_2d.c,v $ */
41 /* $Revision: 1.1 $ */
42 /* $Date: 2006/12/31 21:25:53 $ */
43