20060303

1 files changed, 42 insertions, 0 deletions

diff --git a/os/boot/rpcg/crc32.c b/os/boot/rpcg/crc32.c
new file mode 100644
index 00000000..78bdacba
--- /dev/null
+++ b/os/boot/rpcg/crc32.c
@@ -0,0 +1,42 @@
+#include "boot.h"
+
+/*
+ * from Rob Warnock
+ */
+static	ulong	crc32tab[256];	/* initialised on first call to crc32 */
+
+enum {
+	CRC32POLY = 0x04c11db7     /* AUTODIN II, Ethernet, & FDDI */
+};
+
+/*
+ * Build auxiliary table for parallel byte-at-a-time CRC-32.
+ */
+static void
+initcrc32(void)
+{
+	int i, j;
+	ulong c;
+
+	for(i = 0; i < 256; i++) {
+		for(c = i << 24, j = 8; j > 0; j--)
+			if(c & (1<<31))
+				c = (c<<1) ^ CRC32POLY;
+			else
+				c <<= 1;
+		crc32tab[i] = c;
+	}
+}
+
+ulong
+crc32(void *buf, int n, ulong crc)
+{
+	uchar *p;
+
+	if(crc32tab[1] == 0)
+		initcrc32();
+	crc = ~crc;
+	for(p = buf; --n >= 0;)
+		crc = (crc << 8) ^ crc32tab[(crc >> 24) ^ *p++];
+	return ~crc;
+}