source/libs/gmp/gmp-src/gen-jacobitab.c

   1 /* gen-jacobi.c
   2
   3    Contributed to the GNU project by Niels Möller.
   4
   5 Copyright 2010 Free Software Foundation, Inc.
   6
   7 This file is part of the GNU MP Library.
   8
   9 The GNU MP Library is free software; you can redistribute it and/or modify
  10 it under the terms of either:
  11
  12   * the GNU Lesser General Public License as published by the Free
  13     Software Foundation; either version 3 of the License, or (at your
  14     option) any later version.
  15
  16 or
  17
  18   * the GNU General Public License as published by the Free Software
  19     Foundation; either version 2 of the License, or (at your option) any
  20     later version.
  21
  22 or both in parallel, as here.
  23
  24 The GNU MP Library is distributed in the hope that it will be useful, but
  25 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  26 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  27 for more details.
  28
  29 You should have received copies of the GNU General Public License and the
  30 GNU Lesser General Public License along with the GNU MP Library.  If not,
  31 see https://www.gnu.org/licenses/.  */
  32
  33 /* Generate the lookup table needed for fast left-to-right computation
  34    of the Jacobi symbol. */
  35
  36 #include <assert.h>
  37 #include <stdio.h>
  38 #include <stdlib.h>
  39
  40 static const struct
  41 {
  42   unsigned char a;
  43   unsigned char b;
  44 } decode_table[13] = {
  45   /*  0 */ { 0, 1 },
  46   /*  1 */ { 0, 3 },
  47   /*  2 */ { 1, 1 },
  48   /*  3 */ { 1, 3 },
  49   /*  4 */ { 2, 1 },
  50   /*  5 */ { 2, 3 },
  51   /*  6 */ { 3, 1 },
  52   /*  7 */ { 3, 3 }, /* d = 1 */
  53   /*  8 */ { 1, 0 },
  54   /*  9 */ { 1, 2 },
  55   /* 10 */ { 3, 0 },
  56   /* 11 */ { 3, 2 },
  57   /* 12 */ { 3, 3 }, /* d = 0 */
  58
  59 };
  60 #define JACOBI_A(bits) (decode_table[(bits)>>1].a)
  61 #define JACOBI_B(bits) (decode_table[(bits)>>1].b)
  62
  63 #define JACOBI_E(bits) ((bits) & 1)
  64 #define JACOBI_D(bits) (((bits)>>1) == 7) /* Gives 0 for don't care states. */
  65
  66 static unsigned
  67 encode (unsigned a, unsigned b, unsigned d)
  68 {
  69   unsigned i;
  70
  71   assert (d < 2);
  72   assert (a < 4);
  73   assert (b < 4);
  74   assert ( (a | b ) & 1);
  75
  76   if (a == 3 && b == 3)
  77     return d ? 7 : 12;
  78
  79   for (i = 0; i < 12; i++)
  80     if (decode_table[i].a == a
  81         && decode_table[i].b == b)
  82       return i;
  83
  84   abort ();
  85 }
  86
  87 int
  88 main (int argc, char **argv)
  89 {
  90   unsigned bits;
  91
  92   for (bits = 0; bits < 208; bits++)
  93     {
  94       unsigned e, a, b, d_old, d, q;
  95
  96       if (bits && !(bits & 0xf))
  97         printf("\n");
  98
  99       q = bits & 3;
 100       d = (bits >> 2) & 1;
 101
 102       e = JACOBI_E (bits >> 3);
 103       a = JACOBI_A (bits >> 3);
 104       b = JACOBI_B (bits >> 3);
 105       d_old = JACOBI_D (bits >> 3);
 106
 107       if (d != d_old && a == 3 && b == 3)
 108         e ^= 1;
 109
 110       if (d == 1)
 111         {
 112           if (b == 2)
 113             e ^= (q & (a >> 1)) ^ (q >> 1);
 114           a = (a - q * b) & 3;
 115         }
 116       else
 117         {
 118           if (a == 2)
 119             e ^= (q & (b >> 1)) ^ (q >> 1);
 120           b = (b - q * a) & 3;
 121         }
 122
 123       printf("%2d,", (encode (a, b, d) << 1) | e);
 124     }
 125   printf("\n");
 126
 127   return 0;
 128 }