Mercurial > dropbear
view libtommath/bn_s_mp_sub.c @ 406:2448ae3e75b5
Fix leak of keybuf in recv_msg_userauth_pk_ok, courtesy of Klocwork
author | Matt Johnston <matt@ucc.asn.au> |
---|---|
date | Sat, 03 Feb 2007 13:31:01 +0000 |
parents | eed26cff980b |
children | 5ff8218bcee9 |
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#include <tommath.h> #ifdef BN_S_MP_SUB_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.org */ /* low level subtraction (assumes |a| > |b|), HAC pp.595 Algorithm 14.9 */ int s_mp_sub (mp_int * a, mp_int * b, mp_int * c) { int olduse, res, min, max; /* find sizes */ min = b->used; max = a->used; /* init result */ if (c->alloc < max) { if ((res = mp_grow (c, max)) != MP_OKAY) { return res; } } olduse = c->used; c->used = max; { register mp_digit u, *tmpa, *tmpb, *tmpc; register int i; /* alias for digit pointers */ tmpa = a->dp; tmpb = b->dp; tmpc = c->dp; /* set carry to zero */ u = 0; for (i = 0; i < min; i++) { /* T[i] = A[i] - B[i] - U */ *tmpc = *tmpa++ - *tmpb++ - u; /* U = carry bit of T[i] * Note this saves performing an AND operation since * if a carry does occur it will propagate all the way to the * MSB. As a result a single shift is enough to get the carry */ u = *tmpc >> ((mp_digit)(CHAR_BIT * sizeof (mp_digit) - 1)); /* Clear carry from T[i] */ *tmpc++ &= MP_MASK; } /* now copy higher words if any, e.g. if A has more digits than B */ for (; i < max; i++) { /* T[i] = A[i] - U */ *tmpc = *tmpa++ - u; /* U = carry bit of T[i] */ u = *tmpc >> ((mp_digit)(CHAR_BIT * sizeof (mp_digit) - 1)); /* Clear carry from T[i] */ *tmpc++ &= MP_MASK; } /* clear digits above used (since we may not have grown result above) */ for (i = c->used; i < olduse; i++) { *tmpc++ = 0; } } mp_clamp (c); return MP_OKAY; } #endif