`123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105` ``````#include "tommath_private.h" #ifdef BN_S_MP_ADD_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 */ /* low level addition, based on HAC pp.594, Algorithm 14.7 */ int s_mp_add(const mp_int *a, const mp_int *b, mp_int *c) { const mp_int *x; int olduse, res, min, max; /* find sizes, we let |a| <= |b| which means we have to sort * them. "x" will point to the input with the most digits */ if (a->used > b->used) { min = b->used; max = a->used; x = a; } else { min = a->used; max = b->used; x = b; } /* init result */ if (c->alloc < (max + 1)) { if ((res = mp_grow(c, max + 1)) != MP_OKAY) { return res; } } /* get old used digit count and set new one */ olduse = c->used; c->used = max + 1; { mp_digit u, *tmpa, *tmpb, *tmpc; int i; /* alias for digit pointers */ /* first input */ tmpa = a->dp; /* second input */ tmpb = b->dp; /* destination */ tmpc = c->dp; /* zero the carry */ u = 0; for (i = 0; i < min; i++) { /* Compute the sum at one digit, T[i] = A[i] + B[i] + U */ *tmpc = *tmpa++ + *tmpb++ + u; /* U = carry bit of T[i] */ u = *tmpc >> (mp_digit)DIGIT_BIT; /* take away carry bit from T[i] */ *tmpc++ &= MP_MASK; } /* now copy higher words if any, that is in A+B * if A or B has more digits add those in */ if (min != max) { for (; i < max; i++) { /* T[i] = X[i] + U */ *tmpc = x->dp[i] + u; /* U = carry bit of T[i] */ u = *tmpc >> (mp_digit)DIGIT_BIT; /* take away carry bit from T[i] */ *tmpc++ &= MP_MASK; } } /* add carry */ *tmpc++ = u; /* clear digits above oldused */ for (i = c->used; i < olduse; i++) { *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 */ ``````