37 lines
1.1 KiB
C
37 lines
1.1 KiB
C
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#include "tommath_private.h"
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#ifdef MP_SUB_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/* high level subtraction (handles signs) */
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mp_err mp_sub(const mp_int *a, const mp_int *b, mp_int *c)
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{
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if (a->sign != b->sign) {
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/* subtract a negative from a positive, OR */
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/* subtract a positive from a negative. */
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/* In either case, ADD their magnitudes, */
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/* and use the sign of the first number. */
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c->sign = a->sign;
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return s_mp_add(a, b, c);
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}
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/* subtract a positive from a positive, OR */
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/* subtract a negative from a negative. */
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/* First, take the difference between their */
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/* magnitudes, then... */
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if (mp_cmp_mag(a, b) == MP_LT) {
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/* The second has a larger magnitude */
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/* The result has the *opposite* sign from */
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/* the first number. */
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c->sign = (!mp_isneg(a) ? MP_NEG : MP_ZPOS);
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MP_EXCH(const mp_int *, a, b);
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} else {
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/* The first has a larger or equal magnitude */
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/* Copy the sign from the first */
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c->sign = a->sign;
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}
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return s_mp_sub(a, b, c);
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}
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#endif
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