80 lines
1.5 KiB
C
80 lines
1.5 KiB
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 / 2**b */
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void fp_div_2d(fp_int *a, int b, fp_int *c, fp_int *d)
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{
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fp_digit D, r, rr;
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int x;
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fp_int t;
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/* if the shift count is <= 0 then we do no work */
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if (b <= 0) {
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fp_copy (a, c);
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if (d != NULL) {
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fp_zero (d);
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}
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return;
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}
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fp_init(&t);
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/* get the remainder */
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if (d != NULL) {
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fp_mod_2d (a, b, &t);
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}
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/* copy */
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fp_copy(a, c);
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/* shift by as many digits in the bit count */
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if (b >= (int)DIGIT_BIT) {
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fp_rshd (c, b / DIGIT_BIT);
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}
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/* shift any bit count < DIGIT_BIT */
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D = (fp_digit) (b % DIGIT_BIT);
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if (D != 0) {
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register fp_digit *tmpc, mask, shift;
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/* mask */
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mask = (((fp_digit)1) << D) - 1;
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/* shift for lsb */
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shift = DIGIT_BIT - D;
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/* alias */
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tmpc = c->dp + (c->used - 1);
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/* carry */
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r = 0;
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for (x = c->used - 1; x >= 0; x--) {
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/* get the lower bits of this word in a temp */
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rr = *tmpc & mask;
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/* shift the current word and mix in the carry bits from the previous word */
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*tmpc = (*tmpc >> D) | (r << shift);
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--tmpc;
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/* set the carry to the carry bits of the current word found above */
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r = rr;
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}
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}
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fp_clamp (c);
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if (d != NULL) {
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fp_copy (&t, d);
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}
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}
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/* $Source$ */
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/* $Revision$ */
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/* $Date$ */
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