# libtom/libtommath

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 /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is library that provides for multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library is 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://libtommath.iahu.ca */ #include /* b = a*2 */ int mp_mul_2 (mp_int * a, mp_int * b) { int x, res, oldused; /* Optimization: should copy and shift at the same time */ if (b->alloc < a->used) { if ((res = mp_grow (b, a->used)) != MP_OKAY) { return res; } } oldused = b->used; b->used = a->used; /* shift any bit count < DIGIT_BIT */ { register mp_digit r, rr, *tmpa, *tmpb; r = 0; tmpa = a->dp; tmpb = b->dp; for (x = 0; x < b->used; x++) { rr = *tmpa >> (DIGIT_BIT - 1); *tmpb++ = ((*tmpa++ << 1) | r) & MP_MASK; r = rr; } /* new leading digit? */ if (r != 0) { if (b->alloc == b->used) { if ((res = mp_grow (b, b->used + 1)) != MP_OKAY) { return res; } } /* add a MSB of 1 */ *tmpb = 1; ++b->used; } tmpb = b->dp + b->used; for (x = b->used; x < oldused; x++) { *tmpb++ = 0; } } return MP_OKAY; }
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