| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: group-exp.c,v 1.1 2004/04/01 12:50:09 mdw Exp $ |
| 4 | * |
| 5 | * Exponentiation for abstract groups |
| 6 | * |
| 7 | * (c) 2004 Straylight/Edgeware |
| 8 | */ |
| 9 | |
| 10 | /*----- Licensing notice --------------------------------------------------* |
| 11 | * |
| 12 | * This file is part of Catacomb. |
| 13 | * |
| 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. |
| 18 | * |
| 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. |
| 23 | * |
| 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, |
| 27 | * MA 02111-1307, USA. |
| 28 | */ |
| 29 | |
| 30 | /*----- Revision history --------------------------------------------------* |
| 31 | * |
| 32 | * $Log: group-exp.c,v $ |
| 33 | * Revision 1.1 2004/04/01 12:50:09 mdw |
| 34 | * Add cyclic group abstraction, with test code. Separate off exponentation |
| 35 | * functions for better static linking. Fix a buttload of bugs on the way. |
| 36 | * Generally ensure that negative exponents do inversion correctly. Add |
| 37 | * table of standard prime-field subgroups. (Binary field subgroups are |
| 38 | * currently unimplemented but easy to add if anyone ever finds a good one.) |
| 39 | * |
| 40 | */ |
| 41 | |
| 42 | /*----- Header files ------------------------------------------------------*/ |
| 43 | |
| 44 | #include "group.h" |
| 45 | #include "group-exp.h" |
| 46 | |
| 47 | /*----- Main code ---------------------------------------------------------*/ |
| 48 | |
| 49 | /* --- @group_stdexp@ --- * |
| 50 | * |
| 51 | * Arguments: @group *g@ = abstract group |
| 52 | * @ge *d@ = destination pointer |
| 53 | * @ge *x@ = base element |
| 54 | * @mp *n@ = exponent |
| 55 | * |
| 56 | * Returns: --- |
| 57 | * |
| 58 | * Use: Computes %$d = x^n$% efficiently. |
| 59 | */ |
| 60 | |
| 61 | void group_stdexp(group *gg, ge *d, ge *x, mp *n) |
| 62 | { |
| 63 | ge *t = G_CREATE(gg); |
| 64 | |
| 65 | G_COPY(gg, t, x); |
| 66 | MP_SHRINK(n); |
| 67 | G_COPY(gg, d, gg->i); |
| 68 | if (n->f & MP_BURN) |
| 69 | G_BURN(gg, t); |
| 70 | if (MP_LEN(n) == 0) |
| 71 | ; |
| 72 | else { |
| 73 | if (n->f & MP_NEG) |
| 74 | G_INV(gg, t, t); |
| 75 | if (MP_LEN(n) < EXP_THRESH) |
| 76 | EXP_SIMPLE(d, t, n); |
| 77 | else |
| 78 | EXP_WINDOW(d, t, n); |
| 79 | } |
| 80 | G_DESTROY(gg, t); |
| 81 | } |
| 82 | |
| 83 | /* --- @group_stdmexp@ --- * |
| 84 | * |
| 85 | * Arguments: @group *g@ = abstract group |
| 86 | * @ge *d@ = destination pointer |
| 87 | * @const group_expfactor *f@ = vector of factors |
| 88 | * @size_t n@ = number of factors |
| 89 | * |
| 90 | * Returns: --- |
| 91 | * |
| 92 | * Use: Computes %$d = g_0^{x_0} g_1^{x_1} \ldots$% efficiently. |
| 93 | */ |
| 94 | |
| 95 | #undef EXP_WINSZ |
| 96 | #define EXP_WINSZ 3 |
| 97 | |
| 98 | void group_stdmexp(group *gg, ge *d, const group_expfactor *f, size_t n) |
| 99 | { |
| 100 | group_expfactor *ff = xmalloc(n * sizeof(group_expfactor)); |
| 101 | size_t i; |
| 102 | |
| 103 | for (i = 0; i < n; i++) { |
| 104 | ff[i].base = G_CREATE(gg); |
| 105 | MP_SHRINK(f[i].exp); |
| 106 | if (f[i].exp->f & MP_NEG) |
| 107 | G_INV(gg, ff[i].base, f[i].base); |
| 108 | else |
| 109 | G_COPY(gg, ff[i].base, f[i].base); |
| 110 | if (f[i].exp->f & MP_BURN) |
| 111 | G_BURN(gg, ff[i].base); |
| 112 | ff[i].exp = f[i].exp; |
| 113 | } |
| 114 | G_COPY(gg, d, gg->i); |
| 115 | EXP_SIMUL(d, ff, n); |
| 116 | for (i = 0; i < n; i++) |
| 117 | G_DESTROY(gg, ff[i].base); |
| 118 | xfree(ff); |
| 119 | } |
| 120 | |
| 121 | /*----- That's all, folks -------------------------------------------------*/ |