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 /* 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@iahu.ca, http://math.libtomcrypt.org */ #include /* b = a/2 */ int mp_div_2(mp_int * a, mp_int * b) { int x, res, oldused; /* copy */ if (b->alloc < a->used) { if ((res = mp_grow (b, a->used)) != MP_OKAY) { return res; } } oldused = b->used; b->used = a->used; { register mp_digit r, rr, *tmpa, *tmpb; /* source alias */ tmpa = a->dp + b->used - 1; /* dest alias */ tmpb = b->dp + b->used - 1; /* carry */ r = 0; for (x = b->used - 1; x >= 0; x--) { /* get the carry for the next iteration */ rr = *tmpa & 1; /* shift the current digit, add in carry and store */ *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1)); /* forward carry to next iteration */ r = rr; } /* zero excess digits */ tmpb = b->dp + b->used; for (x = b->used; x < oldused; x++) { *tmpb++ = 0; } } b->sign = a->sign; mp_clamp (b); return MP_OKAY; }
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