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