1 files changed, 30 insertions, 38 deletions

diff --git a/libgo/go/hash/adler32/adler32.go b/libgo/go/hash/adler32/adler32.go
index 64fe68c..7c80796 100644
--- a/libgo/go/hash/adler32/adler32.go
+++ b/libgo/go/hash/adler32/adler32.go
@@ -3,7 +3,8 @@
 // license that can be found in the LICENSE file.
 
 // Package adler32 implements the Adler-32 checksum.
-// Defined in RFC 1950:
+//
+// It is defined in RFC 1950:
 //	Adler-32 is composed of two sums accumulated per byte: s1 is
 //	the sum of all bytes, s2 is the sum of all s1 values. Both sums
 //	are done modulo 65521. s1 is initialized to 1, s2 to zero.  The
@@ -14,20 +15,22 @@ package adler32
 import "hash"
 
 const (
+	// mod is the largest prime that is less than 65536.
 	mod = 65521
+	// nmax is the largest n such that
+	// 255 * n * (n+1) / 2 + (n+1) * (mod-1) <= 2^32-1.
+	// It is mentioned in RFC 1950 (search for "5552").
+	nmax = 5552
 )
 
 // The size of an Adler-32 checksum in bytes.
 const Size = 4
 
 // digest represents the partial evaluation of a checksum.
-type digest struct {
-	// invariant: (a < mod && b < mod) || a <= b
-	// invariant: a + b + 255 <= 0xffffffff
-	a, b uint32
-}
+// The low 16 bits are s1, the high 16 bits are s2.
+type digest uint32
 
-func (d *digest) Reset() { d.a, d.b = 1, 0 }
+func (d *digest) Reset() { *d = 1 }
 
 // New returns a new hash.Hash32 computing the Adler-32 checksum.
 func New() hash.Hash32 {
@@ -40,47 +43,36 @@ func (d *digest) Size() int { return Size }
 
 func (d *digest) BlockSize() int { return 1 }
 
-// Add p to the running checksum a, b.
-func update(a, b uint32, p []byte) (aa, bb uint32) {
-	for _, pi := range p {
-		a += uint32(pi)
-		b += a
-		// invariant: a <= b
-		if b > (0xffffffff-255)/2 {
-			a %= mod
-			b %= mod
-			// invariant: a < mod && b < mod
-		} else {
-			// invariant: a + b + 255 <= 2 * b + 255 <= 0xffffffff
+// Add p to the running checksum d.
+func update(d digest, p []byte) digest {
+	s1, s2 := uint32(d&0xffff), uint32(d>>16)
+	for len(p) > 0 {
+		var q []byte
+		if len(p) > nmax {
+			p, q = p[:nmax], p[nmax:]
 		}
+		for _, x := range p {
+			s1 += uint32(x)
+			s2 += s1
+		}
+		s1 %= mod
+		s2 %= mod
+		p = q
 	}
-	return a, b
-}
-
-// Return the 32-bit checksum corresponding to a, b.
-func finish(a, b uint32) uint32 {
-	if b >= mod {
-		a %= mod
-		b %= mod
-	}
-	return b<<16 | a
+	return digest(s2<<16 | s1)
 }
 
 func (d *digest) Write(p []byte) (nn int, err error) {
-	d.a, d.b = update(d.a, d.b, p)
+	*d = update(*d, p)
 	return len(p), nil
 }
 
-func (d *digest) Sum32() uint32 { return finish(d.a, d.b) }
+func (d *digest) Sum32() uint32 { return uint32(*d) }
 
 func (d *digest) Sum(in []byte) []byte {
-	s := d.Sum32()
-	in = append(in, byte(s>>24))
-	in = append(in, byte(s>>16))
-	in = append(in, byte(s>>8))
-	in = append(in, byte(s))
-	return in
+	s := uint32(*d)
+	return append(in, byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
 }
 
 // Checksum returns the Adler-32 checksum of data.
-func Checksum(data []byte) uint32 { return finish(update(1, 0, data)) }
+func Checksum(data []byte) uint32 { return uint32(update(1, data)) }