Mercurial > dropbear
annotate bn_mp_reduce_2k.c @ 200:c5c969ed76f3 libtommath
propagate from branch 'au.asn.ucc.matt.ltm-orig' (head 7fa10cba9535de3461cedb14b877c24858826204)
to branch 'au.asn.ucc.matt.dropbear.ltm' (head fc26f60de0370ab0a281fa41a2d13fb17c9d90a8)
| author | Matt Johnston <matt@ucc.asn.au> |
|---|---|
| date | Wed, 11 May 2005 16:15:27 +0000 |
| parents | d8254fc979e9 |
| children |
| rev | line source |
|---|---|
| 142 | 1 #include <tommath.h> |
| 2 #ifdef BN_MP_REDUCE_2K_C | |
| 2 | 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 /* reduces a modulo n where n is of the form 2**p - d */ | |
|
190
d8254fc979e9
Initial import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
142
diff
changeset
|
19 int mp_reduce_2k(mp_int *a, mp_int *n, mp_digit d) |
| 2 | 20 { |
| 21 mp_int q; | |
| 22 int p, res; | |
| 23 | |
| 24 if ((res = mp_init(&q)) != MP_OKAY) { | |
| 25 return res; | |
| 26 } | |
| 27 | |
| 28 p = mp_count_bits(n); | |
| 29 top: | |
| 30 /* q = a/2**p, a = a mod 2**p */ | |
| 31 if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) { | |
| 32 goto ERR; | |
| 33 } | |
| 34 | |
| 35 if (d != 1) { | |
| 36 /* q = q * d */ | |
| 37 if ((res = mp_mul_d(&q, d, &q)) != MP_OKAY) { | |
| 38 goto ERR; | |
| 39 } | |
| 40 } | |
| 41 | |
| 42 /* a = a + q */ | |
| 43 if ((res = s_mp_add(a, &q, a)) != MP_OKAY) { | |
| 44 goto ERR; | |
| 45 } | |
| 46 | |
| 47 if (mp_cmp_mag(a, n) != MP_LT) { | |
| 48 s_mp_sub(a, n, a); | |
| 49 goto top; | |
| 50 } | |
| 51 | |
| 52 ERR: | |
| 53 mp_clear(&q); | |
| 54 return res; | |
| 55 } | |
| 56 | |
| 142 | 57 #endif |