[digest] Add generic CRC32 function

Signed-off-by: Marty Connor <mdc@etherboot.org>

src/crypto/crc32.c

@@ -0,0 +1,54 @@
+/*
+ * Little-endian CRC32 implementation.
+ *
+ * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <gpxe/crc32.h>
+
+#define CRCPOLY		0xedb88320
+
+/**
+ * Calculate 32-bit little-endian CRC checksum
+ *
+ * @v seed	Initial value
+ * @v data	Data to checksum
+ * @v len	Length of data
+ *
+ * Usually @a seed is initially zero or all one bits, depending on the
+ * protocol. To continue a CRC checksum over multiple calls, pass the
+ * return value from one call as the @a seed parameter to the next.
+ */
+u32 crc32_le ( u32 seed, const void *data, size_t len )
+{
+	u32 crc = seed;
+	const u8 *src = data;
+	u32 mult;
+	int i;
+
+	while ( len-- ) {
+		crc ^= *src++;
+		for ( i = 0; i < 8; i++ ) {
+			mult = ( crc & 1 ) ? CRCPOLY : 0;
+			crc = ( crc >> 1 ) ^ mult;
+		}
+	}
+
+	return crc;
+}

src/include/gpxe/crc32.h

@@ -0,0 +1,10 @@
+#ifndef _GPXE_CRC32_H
+#define _GPXE_CRC32_H
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+
+u32 crc32_le ( u32 seed, const void *data, size_t len );
+
+#endif