104 lines
3.0 KiB
C
104 lines
3.0 KiB
C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
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*/
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#include <tommath.h>
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/* Check if remainders are possible squares - fast exclude non-squares */
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static const char rem_128[128] = {
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0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1
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};
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static const char rem_105[105] = {
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0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1,
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0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1,
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0, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1,
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0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1,
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1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1,
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1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1
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};
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/* Store non-zero to ret if arg is square, and zero if not */
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int mp_is_square(mp_int *arg,int *ret)
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{
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int res;
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mp_digit c;
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mp_int t;
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unsigned long r;
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/* Default to Non-square :) */
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*ret = MP_NO;
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if (arg->sign == MP_NEG) {
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return MP_VAL;
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}
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/* digits used? (TSD) */
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if (arg->used == 0) {
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return MP_OKAY;
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}
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/* First check mod 128 (suppose that DIGIT_BIT is at least 7) */
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if (rem_128[127 & DIGIT(arg,0)] == 1) {
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return MP_OKAY;
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}
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/* Next check mod 105 (3*5*7) */
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if ((res = mp_mod_d(arg,105,&c)) != MP_OKAY) {
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return res;
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}
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if (rem_105[c] == 1) {
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return MP_OKAY;
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}
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/* product of primes less than 2^31 */
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if ((res = mp_init_set_int(&t,11L*13L*17L*19L*23L*29L*31L)) != MP_OKAY) {
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return res;
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}
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if ((res = mp_mod(arg,&t,&t)) != MP_OKAY) {
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goto ERR;
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}
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r = mp_get_int(&t);
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/* Check for other prime modules, note it's not an ERROR but we must
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* free "t" so the easiest way is to goto ERR. We know that res
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* is already equal to MP_OKAY from the mp_mod call
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*/
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if ( (1L<<(r%11)) & 0x5C4L ) goto ERR;
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if ( (1L<<(r%13)) & 0x9E4L ) goto ERR;
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if ( (1L<<(r%17)) & 0x5CE8L ) goto ERR;
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if ( (1L<<(r%19)) & 0x4F50CL ) goto ERR;
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if ( (1L<<(r%23)) & 0x7ACCA0L ) goto ERR;
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if ( (1L<<(r%29)) & 0xC2EDD0CL ) goto ERR;
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if ( (1L<<(r%31)) & 0x6DE2B848L ) goto ERR;
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/* Final check - is sqr(sqrt(arg)) == arg ? */
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if ((res = mp_sqrt(arg,&t)) != MP_OKAY) {
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goto ERR;
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}
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if ((res = mp_sqr(&t,&t)) != MP_OKAY) {
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goto ERR;
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}
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*ret = (mp_cmp_mag(&t,arg) == MP_EQ) ? MP_YES : MP_NO;
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ERR:mp_clear(&t);
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return res;
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}
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