## Mercurial > dropbear

### view libtommath/bn_mp_mul_2.c @ 709:abd99ecd7ec2

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use an empty writebuf rather than a NULL one

author | Matt Johnston <matt@ucc.asn.au> |
---|---|

date | Wed, 20 Mar 2013 22:31:07 +0800 |

parents | 5ff8218bcee9 |

children | 60fc6476e044 |

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#include <tommath.h> #ifdef BN_MP_MUL_2_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, [email protected], http://math.libtomcrypt.com */ /* b = a*2 */ int mp_mul_2(mp_int * a, mp_int * b) { int x, res, oldused; /* grow to accomodate result */ if (b->alloc < a->used + 1) { if ((res = mp_grow (b, a->used + 1)) != MP_OKAY) { return res; } } oldused = b->used; b->used = a->used; { register mp_digit r, rr, *tmpa, *tmpb; /* alias for source */ tmpa = a->dp; /* alias for dest */ tmpb = b->dp; /* carry */ r = 0; for (x = 0; x < a->used; x++) { /* get what will be the *next* carry bit from the * MSB of the current digit */ rr = *tmpa >> ((mp_digit)(DIGIT_BIT - 1)); /* now shift up this digit, add in the carry [from the previous] */ *tmpb++ = ((*tmpa++ << ((mp_digit)1)) | r) & MP_MASK; /* copy the carry that would be from the source * digit into the next iteration */ r = rr; } /* new leading digit? */ if (r != 0) { /* add a MSB which is always 1 at this point */ *tmpb = 1; ++(b->used); } /* now zero any excess digits on the destination * that we didn't write to */ tmpb = b->dp + b->used; for (x = b->used; x < oldused; x++) { *tmpb++ = 0; } } b->sign = a->sign; return MP_OKAY; } #endif /* $Source: /cvs/libtom/libtommath/bn_mp_mul_2.c,v $ */ /* $Revision: 1.3 $ */ /* $Date: 2006/03/31 14:18:44 $ */