99 lines
1.8 KiB
C
99 lines
1.8 KiB
C
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/* 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 "bignum_fast.h"
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static int s_is_power_of_two(fp_digit b, int *p)
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{
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int x;
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/* fast return if no power of two */
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if ((b==0) || (b & (b-1))) {
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return 0;
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}
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for (x = 0; x < DIGIT_BIT; x++) {
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if (b == (((fp_digit)1)<<x)) {
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*p = x;
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return 1;
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}
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}
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return 0;
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}
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/* a/b => cb + d == a */
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int fp_div_d(fp_int *a, fp_digit b, fp_int *c, fp_digit *d)
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{
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fp_int q;
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fp_word w;
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fp_digit t;
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int ix;
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/* cannot divide by zero */
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if (b == 0) {
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return FP_VAL;
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}
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/* quick outs */
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if (b == 1 || fp_iszero(a) == 1) {
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if (d != NULL) {
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*d = 0;
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}
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if (c != NULL) {
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fp_copy(a, c);
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}
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return FP_OKAY;
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}
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/* power of two ? */
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if (s_is_power_of_two(b, &ix) == 1) {
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if (d != NULL) {
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*d = a->dp[0] & ((((fp_digit)1)<<ix) - 1);
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}
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if (c != NULL) {
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fp_div_2d(a, ix, c, NULL);
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}
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return FP_OKAY;
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}
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/* no easy answer [c'est la vie]. Just division */
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fp_init(&q);
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q.used = a->used;
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q.sign = a->sign;
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w = 0;
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for (ix = a->used - 1; ix >= 0; ix--) {
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w = (w << ((fp_word)DIGIT_BIT)) | ((fp_word)a->dp[ix]);
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if (w >= b) {
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t = (fp_digit)(w / b);
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w -= ((fp_word)t) * ((fp_word)b);
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} else {
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t = 0;
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}
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q.dp[ix] = (fp_digit)t;
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}
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if (d != NULL) {
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*d = (fp_digit)w;
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}
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if (c != NULL) {
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fp_clamp(&q);
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fp_copy(&q, c);
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}
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return FP_OKAY;
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}
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/* $Source: /cvs/libtom/tomsfastmath/src/divide/fp_div_d.c,v $ */
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/* $Revision: 1.2 $ */
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/* $Date: 2007/01/12 15:13:54 $ */
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