# public libtom /libtommath

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file 73 lines (60 sloc) 1.752 kb
 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 `/* 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 */intmp_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;  c->sign = a->sign;  {    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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