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      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 }
    102