3 * $Id: mpbarrett.c,v 1.1 1999/12/10 23:21:59 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 1.1 1999/12/10 23:21:59 mdw
34 * Barrett reduction support: works with even moduli.
38 /*----- Header files ------------------------------------------------------*/
41 #include "mpbarrett.h"
43 /*----- Main code ---------------------------------------------------------*/
45 /* --- @mpbarrett_create@ --- *
47 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
48 * @mp *m@ = modulus to work to
53 * Use: Initializes a Barrett reduction context ready for use.
56 void mpbarrett_create(mpbarrett
*mb
, mp
*m
)
60 /* --- Validate the arguments --- */
62 assert(((void)"Barrett modulus must be positive", (m
->f
& MP_NEG
) == 0));
64 /* --- Compute %$\mu$% --- */
69 b
= mp_lsl(MP_NEW
, MP_ONE
, 2 * MPW_BITS
* mb
->k
);
74 /* --- @mpbarrett_destroy@ --- *
76 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
80 * Use: Destroys a Barrett reduction context releasing any resources
84 void mpbarrett_destroy(mpbarrett
*mb
)
90 /* --- @mpbarrett_reduce@ --- *
92 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
93 * @mp *d@ = destination for result
94 * @mp *m@ = number to reduce
96 * Returns: The residue of @m@ modulo the number in the reduction
99 * Use: Performs an efficient modular reduction. The argument is
100 * assumed to be positive.
103 mp
*mpbarrett_reduce(mpbarrett
*mb
, mp
*d
, mp
*m
)
108 /* --- Special case if @m@ is too small --- */
116 /* --- First stage --- */
120 mp_build(&qq
, m
->v
+ (k
- 1), m
->vl
);
121 q
= mp_mul(MP_NEW
, &qq
, mb
->mu
);
122 q
= mp_lsr(q
, q
, MPW_BITS
* (k
+ 1));
125 /* --- Second stage --- */
132 if (MP_LEN(m
) <= k
+ 1)
136 r
= mp_create(k
+ 1);
137 mpx_umul(r
->v
, r
->vl
, q
->v
, q
->vl
, mb
->m
->v
, mb
->m
->vl
);
138 r
->f
= (q
->f
| mb
->m
->f
) & MP_BURN
;
140 mpx_usub(d
->v
, d
->vl
, m
->v
, mvl
, r
->v
, r
->vl
);
141 d
->f
= (m
->f
| r
->f
) & MP_BURN
;
147 /* --- Final stage --- */
150 while (MPX_UCMP(d
->v
, d
->vl
, >=, mb
->m
->v
, mb
->m
->vl
))
151 mpx_usub(d
->v
, d
->vl
, d
->v
, d
->vl
, mb
->m
->v
, mb
->m
->vl
);
157 /* --- @mpbarrett_exp@ --- *
159 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
160 * @mp *d@ = fake destination
164 * Returns: Result, %$a^e \bmod m$%.
167 mp
*mpbarrett_exp(mpbarrett
*mb
, mp
*d
, mp
*a
, mp
*e
)
181 dd
= mp_sqr(spare
, a
);
182 dd
= mpbarrett_reduce(mb
, dd
, dd
);
186 dd
= mp_mul(spare
, x
, a
);
187 dd
= mpbarrett_reduce(mb
, dd
, dd
);
204 /*----- Test rig ----------------------------------------------------------*/
208 static int vmod(dstr
*v
)
210 mp
*x
= *(mp
**)v
[0].buf
;
211 mp
*n
= *(mp
**)v
[1].buf
;
212 mp
*r
= *(mp
**)v
[2].buf
;
217 mpbarrett_create(&mb
, n
);
218 s
= mpbarrett_reduce(&mb
, MP_NEW
, x
);
220 if (MP_CMP(s
, !=, r
)) {
221 fputs("\n*** barrett reduction failure\n", stderr
);
222 fputs("x = ", stderr
); mp_writefile(x
, stderr
, 10); fputc('\n', stderr
);
223 fputs("n = ", stderr
); mp_writefile(n
, stderr
, 10); fputc('\n', stderr
);
224 fputs("r = ", stderr
); mp_writefile(r
, stderr
, 10); fputc('\n', stderr
);
225 fputs("s = ", stderr
); mp_writefile(s
, stderr
, 10); fputc('\n', stderr
);
229 mpbarrett_destroy(&mb
);
234 assert(mparena_count(MPARENA_GLOBAL
) == 0);
238 static int vexp(dstr
*v
)
240 mp
*m
= *(mp
**)v
[0].buf
;
241 mp
*a
= *(mp
**)v
[1].buf
;
242 mp
*b
= *(mp
**)v
[2].buf
;
243 mp
*r
= *(mp
**)v
[3].buf
;
248 mpbarrett_create(&mb
, m
);
250 mr
= mpbarrett_exp(&mb
, MP_NEW
, a
, b
);
252 if (MP_CMP(mr
, !=, r
)) {
253 fputs("\n*** barrett modexp failed", stderr
);
254 fputs("\n m = ", stderr
); mp_writefile(m
, stderr
, 10);
255 fputs("\n a = ", stderr
); mp_writefile(a
, stderr
, 10);
256 fputs("\n e = ", stderr
); mp_writefile(b
, stderr
, 10);
257 fputs("\n r = ", stderr
); mp_writefile(r
, stderr
, 10);
258 fputs("\nmr = ", stderr
); mp_writefile(mr
, stderr
, 10);
268 mpbarrett_destroy(&mb
);
269 assert(mparena_count(MPARENA_GLOBAL
) == 0);
273 static test_chunk tests
[] = {
274 { "mpbarrett-reduce", vmod
, { &type_mp
, &type_mp
, &type_mp
, 0 } },
275 { "mpbarrett-exp", vexp
, { &type_mp
, &type_mp
, &type_mp
, &type_mp
, 0 } },
279 int main(int argc
, char *argv
[])
282 test_run(argc
, argv
, tests
, SRCDIR
"/tests/mpbarrett");
288 /*----- That's all, folks -------------------------------------------------*/