Mercurial > dropbear
annotate bn_s_mp_mul_digs.c @ 190:d8254fc979e9 libtommath-orig LTM_0.35
Initial import of libtommath 0.35
| author | Matt Johnston <matt@ucc.asn.au> |
|---|---|
| date | Fri, 06 May 2005 08:59:30 +0000 |
| parents | d29b64170cf0 |
| children |
| rev | line source |
|---|---|
| 142 | 1 #include <tommath.h> |
| 2 #ifdef BN_S_MP_MUL_DIGS_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 /* multiplies |a| * |b| and only computes upto digs digits of result | |
| 19 * HAC pp. 595, Algorithm 14.12 Modified so you can control how | |
| 20 * many digits of output are created. | |
| 21 */ | |
|
190
d8254fc979e9
Initial import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
142
diff
changeset
|
22 int s_mp_mul_digs (mp_int * a, mp_int * b, mp_int * c, int digs) |
| 2 | 23 { |
| 24 mp_int t; | |
| 25 int res, pa, pb, ix, iy; | |
| 26 mp_digit u; | |
| 27 mp_word r; | |
| 28 mp_digit tmpx, *tmpt, *tmpy; | |
| 29 | |
| 30 /* can we use the fast multiplier? */ | |
| 31 if (((digs) < MP_WARRAY) && | |
| 32 MIN (a->used, b->used) < | |
| 33 (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) { | |
| 34 return fast_s_mp_mul_digs (a, b, c, digs); | |
| 35 } | |
| 36 | |
| 37 if ((res = mp_init_size (&t, digs)) != MP_OKAY) { | |
| 38 return res; | |
| 39 } | |
| 40 t.used = digs; | |
| 41 | |
| 42 /* compute the digits of the product directly */ | |
| 43 pa = a->used; | |
| 44 for (ix = 0; ix < pa; ix++) { | |
| 45 /* set the carry to zero */ | |
| 46 u = 0; | |
| 47 | |
| 48 /* limit ourselves to making digs digits of output */ | |
| 49 pb = MIN (b->used, digs - ix); | |
| 50 | |
| 51 /* setup some aliases */ | |
| 52 /* copy of the digit from a used within the nested loop */ | |
| 53 tmpx = a->dp[ix]; | |
| 54 | |
| 55 /* an alias for the destination shifted ix places */ | |
| 56 tmpt = t.dp + ix; | |
| 57 | |
| 58 /* an alias for the digits of b */ | |
| 59 tmpy = b->dp; | |
| 60 | |
| 61 /* compute the columns of the output and propagate the carry */ | |
| 62 for (iy = 0; iy < pb; iy++) { | |
| 63 /* compute the column as a mp_word */ | |
| 64 r = ((mp_word)*tmpt) + | |
| 65 ((mp_word)tmpx) * ((mp_word)*tmpy++) + | |
| 66 ((mp_word) u); | |
| 67 | |
| 68 /* the new column is the lower part of the result */ | |
| 69 *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK)); | |
| 70 | |
| 71 /* get the carry word from the result */ | |
| 72 u = (mp_digit) (r >> ((mp_word) DIGIT_BIT)); | |
| 73 } | |
| 74 /* set carry if it is placed below digs */ | |
| 75 if (ix + iy < digs) { | |
| 76 *tmpt = u; | |
| 77 } | |
| 78 } | |
| 79 | |
| 80 mp_clamp (&t); | |
| 81 mp_exch (&t, c); | |
| 82 | |
| 83 mp_clear (&t); | |
| 84 return MP_OKAY; | |
| 85 } | |
| 142 | 86 #endif |