Mercurial > dropbear
comparison tomsfastmath/src/addsub/fp_sub.c @ 643:a362b62d38b2 dropbear-tfm
Add tomsfastmath from git rev bfa4582842bc3bab42e4be4aed5703437049502a
with Makefile.in renamed
| author | Matt Johnston <matt@ucc.asn.au> |
|---|---|
| date | Wed, 23 Nov 2011 18:10:20 +0700 |
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| children |
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| 642:33fd2f3499d2 | 643:a362b62d38b2 |
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| 1 /* TomsFastMath, a fast ISO C bignum library. | |
| 2 * | |
| 3 * This project is meant to fill in where LibTomMath | |
| 4 * falls short. That is speed ;-) | |
| 5 * | |
| 6 * This project is public domain and free for all purposes. | |
| 7 * | |
| 8 * Tom St Denis, [email protected] | |
| 9 */ | |
| 10 #include <tfm.h> | |
| 11 | |
| 12 /* c = a - b */ | |
| 13 void fp_sub(fp_int *a, fp_int *b, fp_int *c) | |
| 14 { | |
| 15 int sa, sb; | |
| 16 | |
| 17 sa = a->sign; | |
| 18 sb = b->sign; | |
| 19 | |
| 20 if (sa != sb) { | |
| 21 /* subtract a negative from a positive, OR */ | |
| 22 /* subtract a positive from a negative. */ | |
| 23 /* In either case, ADD their magnitudes, */ | |
| 24 /* and use the sign of the first number. */ | |
| 25 c->sign = sa; | |
| 26 s_fp_add (a, b, c); | |
| 27 } else { | |
| 28 /* subtract a positive from a positive, OR */ | |
| 29 /* subtract a negative from a negative. */ | |
| 30 /* First, take the difference between their */ | |
| 31 /* magnitudes, then... */ | |
| 32 if (fp_cmp_mag (a, b) != FP_LT) { | |
| 33 /* Copy the sign from the first */ | |
| 34 c->sign = sa; | |
| 35 /* The first has a larger or equal magnitude */ | |
| 36 s_fp_sub (a, b, c); | |
| 37 } else { | |
| 38 /* The result has the *opposite* sign from */ | |
| 39 /* the first number. */ | |
| 40 c->sign = (sa == FP_ZPOS) ? FP_NEG : FP_ZPOS; | |
| 41 /* The second has a larger magnitude */ | |
| 42 s_fp_sub (b, a, c); | |
| 43 } | |
| 44 } | |
| 45 } | |
| 46 | |
| 47 | |
| 48 /* $Source$ */ | |
| 49 /* $Revision$ */ | |
| 50 /* $Date$ */ |