b4b40913c0bab52bce386f38d56a263cf9763f91
3 * $Id: f-niceprime.c,v 1.2 2004/03/27 17:54:11 mdw Exp $
5 * Prime fields with efficient reduction for special-form 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: f-niceprime.c,v $
33 * Revision 1.2 2004/03/27 17:54:11 mdw
34 * Standard curves and curve checking.
36 * Revision 1.1 2004/03/27 00:04:46 mdw
37 * Implement efficient reduction for pleasant-looking primes.
41 /*----- Header files ------------------------------------------------------*/
49 /*----- Data structures ---------------------------------------------------*/
56 /*----- Main code ---------------------------------------------------------*/
58 /* --- Field operations --- */
60 static void fdestroy(field
*ff
)
63 mpreduce_destroy(&f
->r
);
67 static mp
*frand(field
*ff
, mp
*d
, grand
*r
)
70 return (mprand_range(d
, f
->r
.p
, r
, 0));
73 static int fzerop(field
*ff
, mp
*x
)
78 static mp
*fneg(field
*ff
, mp
*d
, mp
*x
)
81 return (mp_sub(d
, f
->r
.p
, x
));
84 static mp
*fadd(field
*ff
, mp
*d
, mp
*x
, mp
*y
)
89 d
= mp_add(d
, d
, f
->r
.p
);
90 else if (MP_CMP(d
, >, f
->r
.p
))
91 d
= mp_sub(d
, d
, f
->r
.p
);
95 static mp
*fsub(field
*ff
, mp
*d
, mp
*x
, mp
*y
)
100 d
= mp_add(d
, d
, f
->r
.p
);
101 else if (MP_CMP(d
, >, f
->r
.p
))
102 d
= mp_sub(d
, d
, f
->r
.p
);
106 static mp
*fmul(field
*ff
, mp
*d
, mp
*x
, mp
*y
)
108 fctx
*f
= (fctx
*)ff
;
110 return (mpreduce_do(&f
->r
, d
, d
));
113 static mp
*fsqr(field
*ff
, mp
*d
, mp
*x
)
115 fctx
*f
= (fctx
*)ff
;
117 return (mpreduce_do(&f
->r
, d
, d
));
120 static mp
*finv(field
*ff
, mp
*d
, mp
*x
)
122 fctx
*f
= (fctx
*)ff
;
123 mp_gcd(0, 0, &d
, f
->r
.p
, x
);
127 static mp
*freduce(field
*ff
, mp
*d
, mp
*x
)
129 fctx
*f
= (fctx
*)ff
;
130 return (mpreduce_do(&f
->r
, d
, x
));
133 static mp
*fsqrt(field
*ff
, mp
*d
, mp
*x
)
135 fctx
*f
= (fctx
*)ff
;
136 return (mp_modsqrt(d
, x
, f
->r
.p
));
139 static mp
*fdbl(field
*ff
, mp
*d
, mp
*x
)
141 fctx
*f
= (fctx
*)ff
;
143 if (MP_CMP(d
, >, f
->r
.p
))
144 d
= mp_sub(d
, d
, f
->r
.p
);
148 static mp
*ftpl(field
*ff
, mp
*d
, mp
*x
)
150 fctx
*f
= (fctx
*)ff
;
151 MP_DEST(d
, MP_LEN(x
) + 1, x
->f
);
152 MPX_UMULN(d
->v
, d
->vl
, x
->v
, x
->vl
, 3);
153 while (MP_CMP(d
, >, f
->r
.p
))
154 d
= mp_sub(d
, d
, f
->r
.p
);
158 static mp
*fqdl(field
*ff
, mp
*d
, mp
*x
)
160 fctx
*f
= (fctx
*)ff
;
162 while (MP_CMP(d
, >, f
->r
.p
))
163 d
= mp_sub(d
, d
, f
->r
.p
);
167 static mp
*fhlv(field
*ff
, mp
*d
, mp
*x
)
169 fctx
*f
= (fctx
*)ff
;
176 d
= mp_add(d
, x
, f
->r
.p
);
179 return (mp_lsr(d
, x
, 1));
182 /* --- Field operations table --- */
184 static field_ops fops
= {
185 FTY_PRIME
, "niceprime",
188 fzerop
, fneg
, fadd
, fsub
, fmul
, fsqr
, finv
, freduce
, fsqrt
,
190 fdbl
, ftpl
, fqdl
, fhlv
193 /* --- @field_niceprime@ --- *
195 * Arguments: @mp *p@ = the characteristic of the field
197 * Returns: A pointer to the field.
199 * Use: Creates a field structure for a prime field of size %$p$%,
200 * using efficient reduction for nice primes.
203 field
*field_niceprime(mp
*p
)
205 fctx
*f
= CREATE(fctx
);
209 f
->f
.nbits
= mp_bits(p
);
210 f
->f
.noctets
= (f
->f
.nbits
+ 7) >> 3;
211 mpreduce_create(&f
->r
, p
);
216 /*----- That's all, folks -------------------------------------------------*/