crc32 algorithm. obtained from dr dobb's journal

http://www.ddj.com/ftp/1992/1992.05/crcman.zip.
copyright 1992 mark r nelson.

1 files changed, 70 insertions, 0 deletions

diff --git a/source/lib/crc32.c b/source/lib/crc32.c
new file mode 100644
index 00000000000..ef9cefea18d
--- /dev/null
+++ b/source/lib/crc32.c
@@ -0,0 +1,70 @@
+/* 
+ * Dr Dobb's Journal: http://www.ddj.com/ftp/1992/1992.05/crcman.zip
+ *
+ * Copyright Mark R. Nelson 1992
+ *
+ */
+
+#include "includes.h"
+
+#define CRC32_POLYNOMIAL     0xEDB88320L
+
+/*****************************************************************
+ Instead of performing a straightforward calculation of the 32 bit
+ CRC using a series of logical operations, this program uses the
+ faster table lookup method.  This routine is called once when the
+ program starts up to build the table which will be used later
+ when calculating the CRC values.
+ *****************************************************************/
+
+static uint32 CRCTable[256];
+
+void crc32_build_table(void)
+{
+	int i;
+	int j;
+	uint32 crc;
+
+	for ( i = 0; i <= 255 ; i++ )
+	{
+		crc = i;
+		for ( j = 8 ; j > 0; j-- )
+		{
+			if ( crc & 1 )
+			{
+				crc = ( crc >> 1 ) ^ CRC32_POLYNOMIAL;
+			}
+			else
+			{
+				crc >>= 1;
+			}
+		}
+		CRCTable[ i ] = crc;
+	}
+}
+
+/*****************************************************************
+ This routine calculates the CRC for a block of data using the
+ table lookup method. 
+ *****************************************************************/
+
+uint32 crc32_calc_buffer( uint32 count, uchar *buffer)
+{
+	uchar *p;
+	uint32 crc;
+
+	p = buffer;
+	crc = 0xffffffff;
+
+	while ( count-- != 0 )
+	{
+		uint32 temp1;
+		uint32 temp2;
+
+		temp1 = ( crc >> 8 ) & 0x00FFFFFFL;
+		temp2 = CRCTable[ ( (int) crc ^ *p++ ) & 0xff ];
+		crc = temp1 ^ temp2;
+	}
+	return crc;
+}
+