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authorRob Landley2006-04-10 17:07:15 +0000
committerRob Landley2006-04-10 17:07:15 +0000
commitc57ec37959390ff2e43faa5e4dd5281b2923ced3 (patch)
tree8325e7bd6a9a270e931b383d33b5901751dd2a5e /libbb/crc32.c
parent998f4493756423877217239d2cc42eb8b83d50b3 (diff)
downloadbusybox-c57ec37959390ff2e43faa5e4dd5281b2923ced3.zip
busybox-c57ec37959390ff2e43faa5e4dd5281b2923ced3.tar.gz
Patch from Rob Sullivan to consolidate crc32 table generation.
Diffstat (limited to 'libbb/crc32.c')
-rw-r--r--libbb/crc32.c40
1 files changed, 40 insertions, 0 deletions
diff --git a/libbb/crc32.c b/libbb/crc32.c
new file mode 100644
index 0000000..0360995
--- /dev/null
+++ b/libbb/crc32.c
@@ -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;
+}