Mercurial > dropbear
diff libtommath/bn_mp_sub.c @ 389:5ff8218bcee9
propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 2af95f00ebd5bb7a28b3817db1218442c935388e)
to branch 'au.asn.ucc.matt.dropbear' (head ecd779509ef23a8cdf64888904fc9b31d78aa933)
author | Matt Johnston <matt@ucc.asn.au> |
---|---|
date | Thu, 11 Jan 2007 03:14:55 +0000 |
parents | eed26cff980b |
children | 60fc6476e044 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/libtommath/bn_mp_sub.c Thu Jan 11 03:14:55 2007 +0000 @@ -0,0 +1,59 @@ +#include <tommath.h> +#ifdef BN_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.com + */ + +/* high level subtraction (handles signs) */ +int +mp_sub (mp_int * a, mp_int * b, mp_int * c) +{ + int sa, sb, res; + + sa = a->sign; + sb = b->sign; + + if (sa != sb) { + /* subtract a negative from a positive, OR */ + /* subtract a positive from a negative. */ + /* In either case, ADD their magnitudes, */ + /* and use the sign of the first number. */ + c->sign = sa; + res = s_mp_add (a, b, c); + } else { + /* subtract a positive from a positive, OR */ + /* subtract a negative from a negative. */ + /* First, take the difference between their */ + /* magnitudes, then... */ + if (mp_cmp_mag (a, b) != MP_LT) { + /* Copy the sign from the first */ + c->sign = sa; + /* The first has a larger or equal magnitude */ + res = s_mp_sub (a, b, c); + } else { + /* The result has the *opposite* sign from */ + /* the first number. */ + c->sign = (sa == MP_ZPOS) ? MP_NEG : MP_ZPOS; + /* The second has a larger magnitude */ + res = s_mp_sub (b, a, c); + } + } + return res; +} + +#endif + +/* $Source: /cvs/libtom/libtommath/bn_mp_sub.c,v $ */ +/* $Revision: 1.3 $ */ +/* $Date: 2006/03/31 14:18:44 $ */