1cd1e66ed3
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@25676 a1c6a512-1295-4272-9138-f99709370657
57 lines
1.3 KiB
C
57 lines
1.3 KiB
C
/*
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* C Implementation: crc32
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*
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* code from http://www.w3.org/TR/PNG/#D-CRCAppendix
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*
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*/
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#include "internal.h"
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/* Table of CRCs of all 8-bit messages. */
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static unsigned long crc_table[256];
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/* Flag: has the table been computed? Initially false. */
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static int crc_table_computed = 0;
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/* Make the table for a fast CRC. */
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static void make_crc_table(void)
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{
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unsigned long c;
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int n, k;
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for (n = 0; n < 256; n++) {
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c = (unsigned long) n;
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for (k = 0; k < 8; k++) {
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if (c & 1)
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c = 0xedb88320L ^ (c >> 1);
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else
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c = c >> 1;
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}
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crc_table[n] = c;
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}
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crc_table_computed = 1;
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}
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/* Update a running CRC with the bytes buf[0..len-1]--the CRC
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should be initialized to all 1's, and the transmitted value
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is the 1's complement of the final running CRC (see the
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crc() routine below). */
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static unsigned long update_crc(unsigned long crc, unsigned char *buf, int len)
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{
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unsigned long c = crc;
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int n;
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if (!crc_table_computed)
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make_crc_table();
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for (n = 0; n < len; n++) {
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c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
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}
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return c;
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}
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/* Return the CRC of the bytes buf[0..len-1]. */
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unsigned long mpc_crc32(unsigned char *buf, int len)
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{
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return update_crc(0xffffffffL, buf, len) ^ 0xffffffffL;
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}
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