66 lines
1.3 KiB
C
66 lines
1.3 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 <tfm_private.h>
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#if FP_GEN_RANDOM_MAX == 0xffffffff
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#define FP_GEN_RANDOM_SHIFT 32
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#elif FP_GEN_RANDOM_MAX == 32767
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/* SHRT_MAX */
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#define FP_GEN_RANDOM_SHIFT 15
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#elif FP_GEN_RANDOM_MAX == 2147483647
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/* INT_MAX */
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#define FP_GEN_RANDOM_SHIFT 31
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#elif !defined(FP_GEN_RANDOM_SHIFT)
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#error Thou shalt define their own valid FP_GEN_RANDOM_SHIFT
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#endif
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/* makes a pseudo-random int of a given size */
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static fp_digit fp_gen_random(void)
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{
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fp_digit d = 0, msk = 0;
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do {
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d <<= FP_GEN_RANDOM_SHIFT;
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d |= ((fp_digit) FP_GEN_RANDOM());
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msk <<= FP_GEN_RANDOM_SHIFT;
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msk |= FP_GEN_RANDOM_MAX;
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} while ((FP_MASK & msk) != FP_MASK);
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d &= FP_MASK;
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return d;
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}
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void fp_rand(fp_int *a, int digits)
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{
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fp_digit d;
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fp_zero(a);
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if (digits <= 0) {
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return;
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}
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/* first place a random non-zero digit */
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do {
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d = fp_gen_random();
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} while (d == 0);
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fp_add_d (a, d, a);
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while (--digits > 0) {
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fp_lshd (a, 1);
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fp_add_d (a, fp_gen_random(), a);
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}
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return;
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}
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/* $Source$ */
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/* $Revision$ */
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/* $Date$ */
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