1 files changed, 72 insertions, 0 deletions
diff --git a/src/libflate/adler.c b/src/libflate/adler.c
new file mode 100644
index 00000000..22fb8f6d
--- /dev/null
+++ b/src/libflate/adler.c
@@ -0,0 +1,72 @@
+#include <u.h>
+#include <libc.h>
+#include <flate.h>
+
+enum
+{
+	ADLERITERS	= 5552,	/* max iters before can overflow 32 bits */
+	ADLERBASE	= 65521 /* largest prime smaller than 65536 */
+};
+
+ulong
+adler32(ulong adler, void *vbuf, int n)
+{
+	ulong s1, s2;
+	uchar *buf, *ebuf;
+	int m;
+
+	buf = vbuf;
+	s1 = adler & 0xffff;
+	s2 = (adler >> 16) & 0xffff;
+	for(; n >= 16; n -= m){
+		m = n;
+		if(m > ADLERITERS)
+			m = ADLERITERS;
+		m &= ~15;
+		for(ebuf = buf + m; buf < ebuf; buf += 16){
+			s1 += buf[0];
+			s2 += s1;
+			s1 += buf[1];
+			s2 += s1;
+			s1 += buf[2];
+			s2 += s1;
+			s1 += buf[3];
+			s2 += s1;
+			s1 += buf[4];
+			s2 += s1;
+			s1 += buf[5];
+			s2 += s1;
+			s1 += buf[6];
+			s2 += s1;
+			s1 += buf[7];
+			s2 += s1;
+			s1 += buf[8];
+			s2 += s1;
+			s1 += buf[9];
+			s2 += s1;
+			s1 += buf[10];
+			s2 += s1;
+			s1 += buf[11];
+			s2 += s1;
+			s1 += buf[12];
+			s2 += s1;
+			s1 += buf[13];
+			s2 += s1;
+			s1 += buf[14];
+			s2 += s1;
+			s1 += buf[15];
+			s2 += s1;
+		}
+		s1 %= ADLERBASE;
+		s2 %= ADLERBASE;
+	}
+	if(n){
+		for(ebuf = buf + n; buf < ebuf; buf++){
+			s1 += buf[0];
+			s2 += s1;
+		}
+		s1 %= ADLERBASE;
+		s2 %= ADLERBASE;
+	}
+	return (s2 << 16) + s1;
+}