Mercurial > dropbear
annotate bn_fast_s_mp_mul_digs.c @ 203:e109027b9edf libtommath LTM_DB_0.46 LTM_DB_0.47
Don't remove ~ files on make clean (and find -type was wrong anyway)
| author | Matt Johnston <matt@ucc.asn.au> |
|---|---|
| date | Wed, 11 May 2005 16:27:28 +0000 |
| parents | d8254fc979e9 |
| children |
| rev | line source |
|---|---|
| 142 | 1 #include <tommath.h> |
| 2 #ifdef BN_FAST_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 /* Fast (comba) multiplier | |
| 19 * | |
| 20 * This is the fast column-array [comba] multiplier. It is | |
| 21 * designed to compute the columns of the product first | |
| 22 * then handle the carries afterwards. This has the effect | |
| 23 * of making the nested loops that compute the columns very | |
| 24 * simple and schedulable on super-scalar processors. | |
| 25 * | |
| 26 * This has been modified to produce a variable number of | |
| 27 * digits of output so if say only a half-product is required | |
| 28 * you don't have to compute the upper half (a feature | |
| 29 * required for fast Barrett reduction). | |
| 30 * | |
| 31 * Based on Algorithm 14.12 on pp.595 of HAC. | |
| 32 * | |
| 33 */ | |
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34 int fast_s_mp_mul_digs (mp_int * a, mp_int * b, mp_int * c, int digs) |
| 2 | 35 { |
| 142 | 36 int olduse, res, pa, ix, iz; |
| 37 mp_digit W[MP_WARRAY]; | |
| 38 register mp_word _W; | |
| 2 | 39 |
| 40 /* grow the destination as required */ | |
| 41 if (c->alloc < digs) { | |
| 42 if ((res = mp_grow (c, digs)) != MP_OKAY) { | |
| 43 return res; | |
| 44 } | |
| 45 } | |
| 46 | |
| 142 | 47 /* number of output digits to produce */ |
| 48 pa = MIN(digs, a->used + b->used); | |
| 2 | 49 |
| 142 | 50 /* clear the carry */ |
| 51 _W = 0; | |
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52 for (ix = 0; ix < pa; ix++) { |
| 142 | 53 int tx, ty; |
| 54 int iy; | |
| 55 mp_digit *tmpx, *tmpy; | |
| 56 | |
| 57 /* get offsets into the two bignums */ | |
| 58 ty = MIN(b->used-1, ix); | |
| 59 tx = ix - ty; | |
| 2 | 60 |
| 142 | 61 /* setup temp aliases */ |
| 62 tmpx = a->dp + tx; | |
| 63 tmpy = b->dp + ty; | |
| 2 | 64 |
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65 /* this is the number of times the loop will iterrate, essentially |
| 142 | 66 while (tx++ < a->used && ty-- >= 0) { ... } |
| 2 | 67 */ |
| 142 | 68 iy = MIN(a->used-tx, ty+1); |
| 2 | 69 |
| 142 | 70 /* execute loop */ |
| 71 for (iz = 0; iz < iy; ++iz) { | |
| 72 _W += ((mp_word)*tmpx++)*((mp_word)*tmpy--); | |
| 73 } | |
| 2 | 74 |
| 142 | 75 /* store term */ |
| 76 W[ix] = ((mp_digit)_W) & MP_MASK; | |
| 2 | 77 |
| 142 | 78 /* make next carry */ |
| 79 _W = _W >> ((mp_word)DIGIT_BIT); | |
| 2 | 80 } |
| 81 | |
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82 /* store final carry */ |
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83 W[ix] = (mp_digit)(_W & MP_MASK); |
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84 |
| 2 | 85 /* setup dest */ |
| 142 | 86 olduse = c->used; |
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87 c->used = pa; |
| 2 | 88 |
| 89 { | |
| 90 register mp_digit *tmpc; | |
| 91 tmpc = c->dp; | |
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92 for (ix = 0; ix < pa+1; ix++) { |
| 2 | 93 /* now extract the previous digit [below the carry] */ |
| 142 | 94 *tmpc++ = W[ix]; |
| 2 | 95 } |
| 96 | |
| 97 /* clear unused digits [that existed in the old copy of c] */ | |
| 98 for (; ix < olduse; ix++) { | |
| 99 *tmpc++ = 0; | |
| 100 } | |
| 101 } | |
| 102 mp_clamp (c); | |
| 103 return MP_OKAY; | |
| 104 } | |
| 142 | 105 #endif |