Patch from Rob Sullivan to consolidate crc32 table generation.

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;
+}