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 #include #ifdef BN_MP_ADD_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. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com */ /* single digit addition */ int mp_add_d (mp_int * a, mp_digit b, mp_int * c) { int res, ix, oldused; mp_digit *tmpa, *tmpc, mu; /* 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 and |a| >= b, call c = |a| - b */ if (a->sign == MP_NEG && (a->used > 1 || a->dp[0] >= b)) { /* temporarily fix sign of a */ a->sign = MP_ZPOS; /* c = |a| - b */ res = mp_sub_d(a, b, c); /* fix sign */ a->sign = c->sign = MP_NEG; /* clamp */ mp_clamp(c); return res; } /* old number of used digits in c */ oldused = c->used; /* sign always positive */ c->sign = MP_ZPOS; /* source alias */ tmpa = a->dp; /* destination alias */ tmpc = c->dp; /* if a is positive */ if (a->sign == MP_ZPOS) { /* add digit, after this we're propagating * the carry. */ *tmpc = *tmpa++ + b; mu = *tmpc >> DIGIT_BIT; *tmpc++ &= MP_MASK; /* now handle rest of the digits */ for (ix = 1; ix < a->used; ix++) { *tmpc = *tmpa++ + mu; mu = *tmpc >> DIGIT_BIT; *tmpc++ &= MP_MASK; } /* set final carry */ ix++; *tmpc++ = mu; /* setup size */ c->used = a->used + 1; } else { /* a was negative and |a| < b */ c->used = 1; /* the result is a single digit */ if (a->used == 1) { *tmpc++ = b - a->dp[0]; } else { *tmpc++ = b; } /* setup count so the clearing of oldused * can fall through correctly */ ix = 1; } /* now zero to oldused */ while (ix++ < oldused) { *tmpc++ = 0; } mp_clamp(c); return MP_OKAY; } #endif /* \$Source: /cvs/libtom/libtommath/bn_mp_add_d.c,v \$ */ /* \$Revision: 1.4 \$ */ /* \$Date: 2006/03/31 14:18:44 \$ */