43 lines
1.0 KiB
C
43 lines
1.0 KiB
C
/* TomsFastMath, a fast ISO C bignum library.
|
|
*
|
|
* This project is meant to fill in where LibTomMath
|
|
* falls short. That is speed ;-)
|
|
*
|
|
* This project is public domain and free for all purposes.
|
|
*
|
|
* Tom St Denis, tomstdenis@gmail.com
|
|
*/
|
|
#include "bignum_fast.h"
|
|
|
|
/* c = a mod 2**d */
|
|
void fp_mod_2d(fp_int *a, int b, fp_int *c)
|
|
{
|
|
int x;
|
|
|
|
/* zero if count less than or equal to zero */
|
|
if (b <= 0) {
|
|
fp_zero(c);
|
|
return;
|
|
}
|
|
|
|
/* get copy of input */
|
|
fp_copy(a, c);
|
|
|
|
/* if 2**d is larger than we just return */
|
|
if (b >= (DIGIT_BIT * a->used)) {
|
|
return;
|
|
}
|
|
|
|
/* zero digits above the last digit of the modulus */
|
|
for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
|
|
c->dp[x] = 0;
|
|
}
|
|
/* clear the digit that is not completely outside/inside the modulus */
|
|
c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) >> (DIGIT_BIT - b);
|
|
fp_clamp (c);
|
|
}
|
|
|
|
/* $Source: /cvs/libtom/tomsfastmath/src/bit/fp_mod_2d.c,v $ */
|
|
/* $Revision: 1.1 $ */
|
|
/* $Date: 2006/12/31 21:25:53 $ */
|