# 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://math.libtomcrypt.org */ #include /* multiply by a digit */ int mp_mul_d (mp_int * a, mp_digit b, mp_int * c) { int res, pa, olduse; /* make sure c is big enough to hold a*b */ pa = a->used; if (c->alloc < pa + 1) { if ((res = mp_grow (c, pa + 1)) != MP_OKAY) { return res; } } /* get the original destinations used count */ olduse = c->used; /* set the new temporary used count */ c->used = pa + 1; { register mp_digit u, *tmpa, *tmpc; register mp_word r; register int ix; /* alias for a->dp [source] */ tmpa = a->dp; /* alias for c->dp [dest] */ tmpc = c->dp; /* zero carry */ u = 0; for (ix = 0; ix < pa; ix++) { /* compute product and carry sum for this term */ r = ((mp_word) u) + ((mp_word) * tmpa++) * ((mp_word) b); /* mask off higher bits to get a single digit */ *tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK)); /* send carry into next iteration */ u = (mp_digit) (r >> ((mp_word) DIGIT_BIT)); } /* store final carry [if any] */ *tmpc++ = u; /* now zero digits above the top */ for (; pa < olduse; pa++) { *tmpc++ = 0; } } mp_clamp (c); return MP_OKAY; }
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