3 * $Id: mpreduce.c,v 1.1 2004/03/27 00:04:46 mdw Exp $
5 * Efficient reduction modulo nice primes
7 * (c) 2004 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Catacomb.
14 * Catacomb is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU Library General Public License as
16 * published by the Free Software Foundation; either version 2 of the
17 * License, or (at your option) any later version.
19 * Catacomb is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22 * GNU Library General Public License for more details.
24 * You should have received a copy of the GNU Library General Public
25 * License along with Catacomb; if not, write to the Free
26 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
30 /*----- Revision history --------------------------------------------------*
32 * $Log: mpreduce.c,v $
33 * Revision 1.1 2004/03/27 00:04:46 mdw
34 * Implement efficient reduction for pleasant-looking primes.
38 /*----- Header files ------------------------------------------------------*/
40 #include <mLib/darray.h>
41 #include <mLib/macros.h>
45 #include "mpreduce-exp.h"
47 /*----- Data structures ---------------------------------------------------*/
49 DA_DECL(instr_v, mpreduce_instr);
51 /*----- Main code ---------------------------------------------------------*/
53 /* --- @mpreduce_create@ --- *
55 * Arguments: @gfreduce *r@ = structure to fill in
56 * @mp *x@ = an integer
60 * Use: Initializes a context structure for reduction.
63 void mpreduce_create(mpreduce *r, mp *p)
66 enum { Z = 0, Z1 = 2, X = 4, X0 = 6 };
73 /* --- Fill in the easy stuff --- */
83 /* --- Stash a new instruction --- */
85 #define INSTR(op_, argx_, argy_) do { \
87 DA(&iv)[DA_LEN(&iv)].op = (op_); \
88 DA(&iv)[DA_LEN(&iv)].argx = (argx_); \
89 DA(&iv)[DA_LEN(&iv)].argy = (argy_); \
93 /* --- Main loop --- *
95 * A simple state machine decomposes @p@ conveniently into positive and
96 * negative powers of 2. The pure form of the state machine is left below
97 * for reference (and in case I need inspiration for a NAF exponentiator).
101 for (i = 0, mp_scan(&sc, p); mp_step(&sc); i++) {
102 switch (st | mp_bit(&sc)) {
103 case Z | 1: st = Z1; break;
104 case Z1 | 0: st = Z; printf("+ %lu\n", i - 1); break;
105 case Z1 | 1: st = X; printf("- %lu\n", i - 1); break;
106 case X | 0: st = X0; break;
107 case X0 | 1: st = X; printf("- %lu\n", i - 1); break;
108 case X0 | 0: st = Z; printf("+ %lu\n", i - 1); break;
111 if (st >= X) printf("+ %lu\n", i);
114 for (i = 0, mp_scan(&sc, p); i < d - 1 && mp_step(&sc); i++) {
115 switch (st | mp_bit(&sc)) {
116 case Z | 1: st = Z1; break;
117 case Z1 | 0: st = Z; op = MPRI_SUB; goto instr;
118 case Z1 | 1: st = X; op = MPRI_ADD; goto instr;
119 case X | 0: st = X0; break;
120 case X0 | 1: st = X; op = MPRI_ADD; goto instr;
121 case X0 | 0: st = Z; op = MPRI_SUB; goto instr;
123 w = (d - i)/MPW_BITS + 1;
124 b = (MPW_BITS + i - d - 1)%MPW_BITS;
125 INSTR(op | !!b, w, b);
128 if ((DA(&iv)[DA_LEN(&iv) - 1].op & ~1u) == MPRI_SUB) {
130 "mpreduce can't handle moduli of the form 2^m + x\n");
136 /* --- Wrap up --- */
140 r->iv = xmalloc(r->in * sizeof(mpreduce_instr));
141 memcpy(r->iv, DA(&iv), r->in * sizeof(mpreduce_instr));
143 r->iv = xmalloc(r->in * 2 * sizeof(mpreduce_instr));
144 for (i = 0; i < r->in; i++) {
145 r->iv[i] = DA(&iv)[i];
146 op = r->iv[i].op & ~1u;
155 r->iv[i + r->in].op = op;
156 r->iv[i + r->in].argx = w;
157 r->iv[i + r->in].argy = b;
163 /* --- @mpreduce_destroy@ --- *
165 * Arguments: @mpreduce *r@ = structure to free
169 * Use: Reclaims the resources from a reduction context.
172 void mpreduce_destroy(mpreduce *r)
178 /* --- @mpreduce_dump@ --- *
180 * Arguments: @mpreduce *r@ = structure to dump
181 * @FILE *fp@ = file to dump on
185 * Use: Dumps a reduction context.
188 void mpreduce_dump(mpreduce *r, FILE *fp)
191 static const char *opname[] = { "add", "addshift", "sub", "subshift" };
193 fprintf(fp, "mod = "); mp_writefile(r->p, fp, 16);
194 fprintf(fp, "\n lim = %lu; s = %d\n", (unsigned long)r->lim, r->s);
195 for (i = 0; i < r->in; i++) {
196 assert(r->iv[i].op < N(opname));
197 fprintf(fp, " %s %lu %lu\n",
199 (unsigned long)r->iv[i].argx,
200 (unsigned long)r->iv[i].argy);
203 fprintf(fp, "tail end charlie\n");
204 for (i = r->in; i < 2 * r->in; i++) {
205 assert(r->iv[i].op < N(opname));
206 fprintf(fp, " %s %lu %lu\n",
208 (unsigned long)r->iv[i].argx,
209 (unsigned long)r->iv[i].argy);
214 /* --- @mpreduce_do@ --- *
216 * Arguments: @mpreduce *r@ = reduction context
217 * @mp *d@ = destination
220 * Returns: Destination, @x@ reduced modulo the reduction poly.
223 static void run(const mpreduce_instr *i, const mpreduce_instr *il,
226 for (; i < il; i++) {
229 mp_build(&vv, v - i->argx, v + 1);
230 printf(" 0x"); mp_writefile(&vv, stdout, 16);
231 printf(" %c (0x%lx << %u) == 0x",
232 (i->op & ~1u) == MPRI_ADD ? '+' : '-',
237 case MPRI_ADD: MPX_UADDN(v - i->argx, v + 1, z); break;
238 case MPRI_ADDLSL: mpx_uaddnlsl(v - i->argx, v + 1, z, i->argy); break;
239 case MPRI_SUB: MPX_USUBN(v - i->argx, v + 1, z); break;
240 case MPRI_SUBLSL: mpx_usubnlsl(v - i->argx, v + 1, z, i->argy); break;
245 mp_build(&vv, v - i->argx, v + 1);
246 mp_writefile(&vv, stdout, 16);
252 mp *mpreduce_do(mpreduce *r, mp *d, mp *x)
255 const mpreduce_instr *il;
259 mp *_r = 0, *_rr = 0;
262 /* --- If source is negative, divide --- */
265 mp_div(0, &d, x, r->p);
269 /* --- Try to reuse the source's space --- */
273 MP_DEST(x, MP_LEN(x), x->f);
275 /* --- Do the reduction --- */
279 mp_div(0, &_r, x, r->p);
285 if (MP_LEN(x) >= r->lim) {
292 run(r->iv, il, vl, z);
295 mp_div(0, &_rr, x, r->p);
296 assert(MP_EQ(_r, _rr));
301 while (*vl >> r->s) {
303 *vl &= ((1 << r->s) - 1);
304 run(r->iv + r->in, il + r->in, vl, z);
307 mp_div(0, &_rr, x, r->p);
308 assert(MP_EQ(_r, _rr));
314 /* --- Finishing touches --- */
317 if (MP_CMP(x, >=, r->p))
318 x = mp_sub(x, x, r->p);
323 assert(MP_EQ(_r, x));
330 /* --- @mpreduce_exp@ --- *
332 * Arguments: @mpreduce *mr@ = pointer to reduction context
333 * @mp *d@ = fake destination
337 * Returns: Result, %$a^e \bmod m$%.
340 mp *mpreduce_exp(mpreduce *mr, mp *d, mp *a, mp *e)
343 mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
348 else if (MP_LEN(e) < EXP_THRESH)
357 /*----- Test rig ----------------------------------------------------------*/
362 #define MP(x) mp_readstring(MP_NEW, #x, 0, 0)
364 static int vreduce(dstr *v)
366 mp *d = *(mp **)v[0].buf;
367 mp *n = *(mp **)v[1].buf;
368 mp *r = *(mp **)v[2].buf;
373 mpreduce_create(&rr, d);
374 c = mpreduce_do(&rr, MP_NEW, n);
376 fprintf(stderr, "\n*** reduction failed\n*** ");
377 mpreduce_dump(&rr, stderr);
378 fprintf(stderr, "\n*** n = "); mp_writefile(n, stderr, 10);
379 fprintf(stderr, "\n*** r = "); mp_writefile(r, stderr, 10);
380 fprintf(stderr, "\n*** c = "); mp_writefile(c, stderr, 10);
381 fprintf(stderr, "\n");
384 mpreduce_destroy(&rr);
385 mp_drop(n); mp_drop(d); mp_drop(r); mp_drop(c);
386 assert(mparena_count(MPARENA_GLOBAL) == 0);
390 static int vmodexp(dstr *v)
392 mp *p = *(mp **)v[0].buf;
393 mp *g = *(mp **)v[1].buf;
394 mp *x = *(mp **)v[2].buf;
395 mp *r = *(mp **)v[3].buf;
400 mpreduce_create(&rr, p);
401 c = mpreduce_exp(&rr, MP_NEW, g, x);
403 fprintf(stderr, "\n*** modexp failed\n*** ");
404 fprintf(stderr, "\n*** p = "); mp_writefile(p, stderr, 10);
405 fprintf(stderr, "\n*** g = "); mp_writefile(g, stderr, 10);
406 fprintf(stderr, "\n*** x = "); mp_writefile(x, stderr, 10);
407 fprintf(stderr, "\n*** c = "); mp_writefile(c, stderr, 10);
408 fprintf(stderr, "\n*** r = "); mp_writefile(r, stderr, 10);
409 fprintf(stderr, "\n");
412 mpreduce_destroy(&rr);
413 mp_drop(p); mp_drop(g); mp_drop(r); mp_drop(x); mp_drop(c);
414 assert(mparena_count(MPARENA_GLOBAL) == 0);
418 static test_chunk defs[] = {
419 { "reduce", vreduce, { &type_mp, &type_mp, &type_mp, 0 } },
420 { "modexp", vmodexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
424 int main(int argc, char *argv[])
426 test_run(argc, argv, defs, SRCDIR"/tests/mpreduce");
432 /*----- That's all, folks -------------------------------------------------*/