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Patch from Rob Sullivan to consolidate crc32 table generation.

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This commit is contained in:
Rob Landley
2006-04-10 17:07:15 +00:00
parent 998f449375
commit c57ec37959
6 changed files with 65 additions and 71 deletions
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2
libbb/Makefile.in
View File

@@ -13,7 +13,7 @@ LIBBB-n:=
LIBBB-y:= \
bb_asprintf.c ask_confirmation.c change_identity.c chomp.c \
compare_string_array.c concat_path_file.c copy_file.c copyfd.c \
create_icmp_socket.c create_icmp6_socket.c \
crc32.c create_icmp_socket.c create_icmp6_socket.c \
device_open.c dump.c error_msg.c error_msg_and_die.c find_mount_point.c \
find_pid_by_name.c find_root_device.c fgets_str.c full_read.c \
full_write.c get_last_path_component.c get_line_from_file.c \

40
libbb/crc32.c Normal file
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@@ -0,0 +1,40 @@
/* vi: set sw=4 ts=4: */
/*
* CRC32 table fill function
* Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com>
* (I can't really claim much credit however, as the algorithm is
* very well-known)
*
* The following function creates a CRC32 table depending on whether
* a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is
* required. Admittedly, there are other CRC32 polynomials floating
* around, but Busybox doesn't use them.
*
* endian = 1: big-endian
* endian = 0: little-endian
*/
#include <stdio.h>
#include <stdlib.h>
#include "libbb.h"
uint32_t *bb_crc32_filltable (int endian) {
uint32_t *crc_table = xmalloc(256 * sizeof(uint32_t));
uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
uint32_t c;
int i, j;
for (i = 0; i < 256; i++) {
c = endian ? (i << 24) : i;
for (j = 8; j; j--) {
if (endian)
c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1);
else
c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1);
}
*crc_table++ = c;
}
return crc_table - 256;
}