e2fsck/gen_crc32table.c

   1 /*
   2  * gen_crc32table.c --- Generate CRC32 tables.
   3  *
   4  * Copyright (C) 2008 Theodore Ts'o.
   5  *
   6  * %Begin-Header%
   7  * This file may be redistributed under the terms of the GNU Public
   8  * License.
   9  * %End-Header%
  10  */
  11
  12 #include <stdio.h>
  13 #include "crc32defs.h"
  14 #include <inttypes.h>
  15
  16 #define ENTRIES_PER_LINE 4
  17
  18 #define LE_TABLE_SIZE (1 << CRC_LE_BITS)
  19 #define BE_TABLE_SIZE (1 << CRC_BE_BITS)
  20
  21 static uint32_t crc32table_le[LE_TABLE_SIZE];
  22 static uint32_t crc32table_be[BE_TABLE_SIZE];
  23
  24 /**
  25  * crc32init_le() - allocate and initialize LE table data
  26  *
  27  * crc is the crc of the byte i; other entries are filled in based on the
  28  * fact that crctable[i^j] = crctable[i] ^ crctable[j].
  29  *
  30  */
  31 static void crc32init_le(void)
  32 {
  33         unsigned i, j;
  34         uint32_t crc = 1;
  35
  36         crc32table_le[0] = 0;
  37
  38         for (i = 1 << (CRC_LE_BITS - 1); i; i >>= 1) {
  39                 crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
  40                 for (j = 0; j < LE_TABLE_SIZE; j += 2 * i)
  41                         crc32table_le[i + j] = crc ^ crc32table_le[j];
  42         }
  43 }
  44
  45 /**
  46  * crc32init_be() - allocate and initialize BE table data
  47  */
  48 static void crc32init_be(void)
  49 {
  50         unsigned i, j;
  51         uint32_t crc = 0x80000000;
  52
  53         crc32table_be[0] = 0;
  54
  55         for (i = 1; i < BE_TABLE_SIZE; i <<= 1) {
  56                 crc = (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE : 0);
  57                 for (j = 0; j < i; j++)
  58                         crc32table_be[i + j] = crc ^ crc32table_be[j];
  59         }
  60 }
  61
  62 static void output_table(uint32_t table[], int len, const char *trans)
  63 {
  64         int i;
  65
  66         for (i = 0; i < len - 1; i++) {
  67                 if (i % ENTRIES_PER_LINE == 0)
  68                         printf("\n");
  69                 printf("%s(0x%8.8xL), ", trans, table[i]);
  70         }
  71         printf("%s(0x%8.8xL)\n", trans, table[len - 1]);
  72 }
  73
  74 #ifdef __GNUC__
  75 #define ATTR(x) __attribute__(x)
  76 #else
  77 #define ATTR(x)
  78 #endif
  79
  80 int main(int argc ATTR((unused)), char** argv ATTR((unused)))
  81 {
  82         printf("/* this file is generated - do not edit */\n\n");
  83
  84         printf("#ifdef UNITTEST\n");
  85         if (CRC_LE_BITS > 1) {
  86                 crc32init_le();
  87                 printf("static const __u32 crc32table_le[] = {");
  88                 output_table(crc32table_le, LE_TABLE_SIZE, "tole");
  89                 printf("};\n");
  90         }
  91         printf("#endif /* UNITTEST */\n");
  92
  93         if (CRC_BE_BITS > 1) {
  94                 crc32init_be();
  95                 printf("static const __u32 crc32table_be[] = {");
  96                 output_table(crc32table_be, BE_TABLE_SIZE, "tobe");
  97                 printf("};\n");
  98         }
  99
 100         return 0;
 101 }