## File: bn_mp_sub_d.c

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libtommath 1.1.0-3
 `123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990` ``````#include "tommath_private.h" #ifdef BN_MP_SUB_D_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * SPDX-License-Identifier: Unlicense */ /* single digit subtraction */ int mp_sub_d(const mp_int *a, mp_digit b, mp_int *c) { mp_digit *tmpa, *tmpc, mu; int res, ix, oldused; /* grow c as required */ if (c->alloc < (a->used + 1)) { if ((res = mp_grow(c, a->used + 1)) != MP_OKAY) { return res; } } /* if a is negative just do an unsigned * addition [with fudged signs] */ if (a->sign == MP_NEG) { mp_int a_ = *a; a_.sign = MP_ZPOS; res = mp_add_d(&a_, b, c); c->sign = MP_NEG; /* clamp */ mp_clamp(c); return res; } /* setup regs */ oldused = c->used; tmpa = a->dp; tmpc = c->dp; /* if a <= b simply fix the single digit */ if (((a->used == 1) && (a->dp <= b)) || (a->used == 0)) { if (a->used == 1) { *tmpc++ = b - *tmpa; } else { *tmpc++ = b; } ix = 1; /* negative/1digit */ c->sign = MP_NEG; c->used = 1; } else { /* positive/size */ c->sign = MP_ZPOS; c->used = a->used; /* subtract first digit */ *tmpc = *tmpa++ - b; mu = *tmpc >> ((sizeof(mp_digit) * (size_t)CHAR_BIT) - 1u); *tmpc++ &= MP_MASK; /* handle rest of the digits */ for (ix = 1; ix < a->used; ix++) { *tmpc = *tmpa++ - mu; mu = *tmpc >> ((sizeof(mp_digit) * (size_t)CHAR_BIT) - 1u); *tmpc++ &= MP_MASK; } } /* zero excess digits */ while (ix++ < oldused) { *tmpc++ = 0; } mp_clamp(c); return MP_OKAY; } #endif /* ref: HEAD -> master, tag: v1.1.0 */ /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */ /* commit time: 2019-01-28 20:32:32 +0100 */ ``````