add libflate

src/libflate/crc.c

@@ -0,0 +1,40 @@
+#include <u.h>
+#include <libc.h>
+#include <flate.h>
+
+ulong*
+mkcrctab(ulong poly)
+{
+	ulong *crctab;
+	ulong crc;
+	int i, j;
+
+	crctab = malloc(256 * sizeof(ulong));
+	if(crctab == nil)
+		return nil;
+
+	for(i = 0; i < 256; i++){
+		crc = i;
+		for(j = 0; j < 8; j++){
+			if(crc & 1)
+				crc = (crc >> 1) ^ poly;
+			else
+				crc >>= 1;
+		}
+		crctab[i] = crc;
+	}
+	return crctab;
+}
+
+ulong
+blockcrc(ulong *crctab, ulong crc, void *vbuf, int n)
+{
+	uchar *buf, *ebuf;
+
+	crc ^= 0xffffffff;
+	buf = vbuf;
+	ebuf = buf + n;
+	while(buf < ebuf)
+		crc = crctab[(crc & 0xff) ^ *buf++] ^ (crc >> 8);
+	return crc ^ 0xffffffff;
+}