denyhosts/clamscan/libclamav/tomsfastmath/bit/fp_mod_2d.c
2022-10-22 18:41:00 +08:00

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 $ */