Performance optimizations for tagcache commit. Still more left to be done.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@9721 a1c6a512-1295-4272-9138-f99709370657

1 files changed, 57 insertions, 0 deletions

diff --git a/firmware/common/crc32.c b/firmware/common/crc32.c
new file mode 100644
index 0000000000..18ee6ac710
--- /dev/null
+++ b/firmware/common/crc32.c
@@ -0,0 +1,57 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2003 Jörg Hohensohn [IDC]Dragon
+ *
+ * All files in this archive are subject to the GNU General Public License.
+ * See the file COPYING in the source tree root for full license agreement.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+
+/* Code copied from firmware_flash plugin. */
+
+/* Tool function to calculate a CRC32 across some buffer */
+/* third argument is either 0xFFFFFFFF to start or value from last piece */
+unsigned crc_32(unsigned char* buf, unsigned len, unsigned crc32)
+{
+    /* CCITT standard polynomial 0x04C11DB7 */
+    static const unsigned crc32_lookup[16] =
+    {   /* lookup table for 4 bits at a time is affordable */
+        0x00000000, 0x04C11DB7, 0x09823B6E, 0x0D4326D9,
+        0x130476DC, 0x17C56B6B, 0x1A864DB2, 0x1E475005,
+        0x2608EDB8, 0x22C9F00F, 0x2F8AD6D6, 0x2B4BCB61,
+        0x350C9B64, 0x31CD86D3, 0x3C8EA00A, 0x384FBDBD
+    };
+
+    unsigned char byte;
+    unsigned t;
+
+    while (len--)
+    {
+        byte = *buf++; /* get one byte of data */
+
+        /* upper nibble of our data */
+        t = crc32 >> 28; /* extract the 4 most significant bits */
+        t ^= byte >> 4; /* XOR in 4 bits of data into the extracted bits */
+        crc32 <<= 4; /* shift the CRC register left 4 bits */
+        crc32 ^= crc32_lookup[t]; /* do the table lookup and XOR the result */
+
+        /* lower nibble of our data */
+        t = crc32 >> 28; /* extract the 4 most significant bits */
+        t ^= byte & 0x0F; /* XOR in 4 bits of data into the extracted bits */
+        crc32 <<= 4; /* shift the CRC register left 4 bits */
+        crc32 ^= crc32_lookup[t]; /* do the table lookup and XOR the result */
+    }
+
+    return crc32;
+}
+