3 * $Id: mpbarrett.c,v 1.3 1999/12/12 15:08:52 mdw Exp $
5 * Barrett modular reduction
7 * (c) 1999 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: mpbarrett.c,v $
33 * Revision 1.3 1999/12/12 15:08:52 mdw
34 * Don't bother shifting %$q$% in @mpbarrett_reduce@, just skip the least
37 * Revision 1.2 1999/12/11 01:50:56 mdw
38 * Improve initialization slightly.
40 * Revision 1.1 1999/12/10 23:21:59 mdw
41 * Barrett reduction support: works with even moduli.
45 /*----- Header files ------------------------------------------------------*/
48 #include "mpbarrett.h"
50 /*----- Main code ---------------------------------------------------------*/
52 /* --- @mpbarrett_create@ --- *
54 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
55 * @mp *m@ = modulus to work to
60 * Use: Initializes a Barrett reduction context ready for use.
63 void mpbarrett_create(mpbarrett
*mb
, mp
*m
)
67 /* --- Validate the arguments --- */
69 assert(((void)"Barrett modulus must be positive", (m
->f
& MP_NEG
) == 0));
71 /* --- Compute %$\mu$% --- */
76 b
= mp_create(2 * mb
->k
+ 1);
77 MPX_ZERO(b
->v
, b
->vl
- 1);
83 /* --- @mpbarrett_destroy@ --- *
85 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
89 * Use: Destroys a Barrett reduction context releasing any resources
93 void mpbarrett_destroy(mpbarrett
*mb
)
99 /* --- @mpbarrett_reduce@ --- *
101 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
102 * @mp *d@ = destination for result
103 * @mp *m@ = number to reduce
105 * Returns: The residue of @m@ modulo the number in the reduction
108 * Use: Performs an efficient modular reduction. The argument is
109 * assumed to be positive.
112 mp
*mpbarrett_reduce(mpbarrett
*mb
, mp
*d
, mp
*m
)
117 /* --- Special case if @m@ is too small --- */
125 /* --- First stage --- */
129 mp_build(&qq
, m
->v
+ (k
- 1), m
->vl
);
130 q
= mp_mul(MP_NEW
, &qq
, mb
->mu
);
131 if (MP_LEN(q
) <= k
) {
138 /* --- Second stage --- */
145 if (MP_LEN(m
) <= k
+ 1)
149 r
= mp_create(k
+ 1);
150 mpx_umul(r
->v
, r
->vl
, q
->v
+ k
+ 1, q
->vl
, mb
->m
->v
, mb
->m
->vl
);
151 r
->f
= (q
->f
| mb
->m
->f
) & MP_BURN
;
153 mpx_usub(d
->v
, d
->vl
, m
->v
, mvl
, r
->v
, r
->vl
);
154 d
->f
= (m
->f
| r
->f
) & MP_BURN
;
160 /* --- Final stage --- */
163 while (MPX_UCMP(d
->v
, d
->vl
, >=, mb
->m
->v
, mb
->m
->vl
))
164 mpx_usub(d
->v
, d
->vl
, d
->v
, d
->vl
, mb
->m
->v
, mb
->m
->vl
);
170 /* --- @mpbarrett_exp@ --- *
172 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
173 * @mp *d@ = fake destination
177 * Returns: Result, %$a^e \bmod m$%.
180 mp
*mpbarrett_exp(mpbarrett
*mb
, mp
*d
, mp
*a
, mp
*e
)
194 dd
= mp_sqr(spare
, a
);
195 dd
= mpbarrett_reduce(mb
, dd
, dd
);
199 dd
= mp_mul(spare
, x
, a
);
200 dd
= mpbarrett_reduce(mb
, dd
, dd
);
217 /*----- Test rig ----------------------------------------------------------*/
221 static int vmod(dstr
*v
)
223 mp
*x
= *(mp
**)v
[0].buf
;
224 mp
*n
= *(mp
**)v
[1].buf
;
225 mp
*r
= *(mp
**)v
[2].buf
;
230 mpbarrett_create(&mb
, n
);
231 s
= mpbarrett_reduce(&mb
, MP_NEW
, x
);
233 if (MP_CMP(s
, !=, r
)) {
234 fputs("\n*** barrett reduction failure\n", stderr
);
235 fputs("x = ", stderr
); mp_writefile(x
, stderr
, 10); fputc('\n', stderr
);
236 fputs("n = ", stderr
); mp_writefile(n
, stderr
, 10); fputc('\n', stderr
);
237 fputs("r = ", stderr
); mp_writefile(r
, stderr
, 10); fputc('\n', stderr
);
238 fputs("s = ", stderr
); mp_writefile(s
, stderr
, 10); fputc('\n', stderr
);
242 mpbarrett_destroy(&mb
);
247 assert(mparena_count(MPARENA_GLOBAL
) == 0);
251 static int vexp(dstr
*v
)
253 mp
*m
= *(mp
**)v
[0].buf
;
254 mp
*a
= *(mp
**)v
[1].buf
;
255 mp
*b
= *(mp
**)v
[2].buf
;
256 mp
*r
= *(mp
**)v
[3].buf
;
261 mpbarrett_create(&mb
, m
);
263 mr
= mpbarrett_exp(&mb
, MP_NEW
, a
, b
);
265 if (MP_CMP(mr
, !=, r
)) {
266 fputs("\n*** barrett modexp failed", stderr
);
267 fputs("\n m = ", stderr
); mp_writefile(m
, stderr
, 10);
268 fputs("\n a = ", stderr
); mp_writefile(a
, stderr
, 10);
269 fputs("\n e = ", stderr
); mp_writefile(b
, stderr
, 10);
270 fputs("\n r = ", stderr
); mp_writefile(r
, stderr
, 10);
271 fputs("\nmr = ", stderr
); mp_writefile(mr
, stderr
, 10);
281 mpbarrett_destroy(&mb
);
282 assert(mparena_count(MPARENA_GLOBAL
) == 0);
286 static test_chunk tests
[] = {
287 { "mpbarrett-reduce", vmod
, { &type_mp
, &type_mp
, &type_mp
, 0 } },
288 { "mpbarrett-exp", vexp
, { &type_mp
, &type_mp
, &type_mp
, &type_mp
, 0 } },
292 int main(int argc
, char *argv
[])
295 test_run(argc
, argv
, tests
, SRCDIR
"/tests/mpbarrett");
301 /*----- That's all, folks -------------------------------------------------*/