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