Mercurial > dropbear
comparison bn_mp_expt_d.c @ 282:91fbc376f010 libtommath-orig libtommath-0.35
Import of libtommath 0.35
From ltm-0.35.tar.bz2 SHA1 of 3f193dbae9351e92d02530994fa18236f7fde01c
| author | Matt Johnston <matt@ucc.asn.au> |
|---|---|
| date | Wed, 08 Mar 2006 13:16:18 +0000 |
| parents | |
| children | 97db060d0ef5 |
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| -1:000000000000 | 282:91fbc376f010 |
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| 1 #include <tommath.h> | |
| 2 #ifdef BN_MP_EXPT_D_C | |
| 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis | |
| 4 * | |
| 5 * LibTomMath is a library that provides multiple-precision | |
| 6 * integer arithmetic as well as number theoretic functionality. | |
| 7 * | |
| 8 * The library was designed directly after the MPI library by | |
| 9 * Michael Fromberger but has been written from scratch with | |
| 10 * additional optimizations in place. | |
| 11 * | |
| 12 * The library is free for all purposes without any express | |
| 13 * guarantee it works. | |
| 14 * | |
| 15 * Tom St Denis, [email protected], http://math.libtomcrypt.org | |
| 16 */ | |
| 17 | |
| 18 /* calculate c = a**b using a square-multiply algorithm */ | |
| 19 int mp_expt_d (mp_int * a, mp_digit b, mp_int * c) | |
| 20 { | |
| 21 int res, x; | |
| 22 mp_int g; | |
| 23 | |
| 24 if ((res = mp_init_copy (&g, a)) != MP_OKAY) { | |
| 25 return res; | |
| 26 } | |
| 27 | |
| 28 /* set initial result */ | |
| 29 mp_set (c, 1); | |
| 30 | |
| 31 for (x = 0; x < (int) DIGIT_BIT; x++) { | |
| 32 /* square */ | |
| 33 if ((res = mp_sqr (c, c)) != MP_OKAY) { | |
| 34 mp_clear (&g); | |
| 35 return res; | |
| 36 } | |
| 37 | |
| 38 /* if the bit is set multiply */ | |
| 39 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) { | |
| 40 if ((res = mp_mul (c, &g, c)) != MP_OKAY) { | |
| 41 mp_clear (&g); | |
| 42 return res; | |
| 43 } | |
| 44 } | |
| 45 | |
| 46 /* shift to next bit */ | |
| 47 b <<= 1; | |
| 48 } | |
| 49 | |
| 50 mp_clear (&g); | |
| 51 return MP_OKAY; | |
| 52 } | |
| 53 #endif |