crypto/sha1: Make sha-1 do block mixup in place

Benchmarks:

benchmark              old ns/op    new ns/op    delta
BenchmarkHash8Bytes          762          674  -11.55%
BenchmarkHash1K             8791         7375  -16.11%
BenchmarkHash8K            65094        54881  -15.69%

benchmark               old MB/s     new MB/s  speedup
BenchmarkHash8Bytes        10.50        11.86    1.13x
BenchmarkHash1K           116.48       138.84    1.19x
BenchmarkHash8K           125.85       149.27    1.19x

R=dave, rsc, iant
CC=golang-dev
https://golang.org/cl/6820096

src/pkg/crypto/sha1/sha1block.go

@@ -16,7 +16,7 @@ const (
 )
 
 func block(dig *digest, p []byte) {
-	var w [80]uint32
+	var w [16]uint32
 
 	h0, h1, h2, h3, h4 := dig.h[0], dig.h[1], dig.h[2], dig.h[3], dig.h[4]
 	for len(p) >= chunk {
@@ -26,42 +26,56 @@ func block(dig *digest, p []byte) {
 			j := i * 4
 			w[i] = uint32(p[j])<<24 | uint32(p[j+1])<<16 | uint32(p[j+2])<<8 | uint32(p[j+3])
 		}
-		for i := 16; i < 80; i++ {
-			tmp := w[i-3] ^ w[i-8] ^ w[i-14] ^ w[i-16]
-			w[i] = tmp<<1 | tmp>>(32-1)
-		}
 
 		a, b, c, d, e := h0, h1, h2, h3, h4
 
 		// Each of the four 20-iteration rounds
 		// differs only in the computation of f and
 		// the choice of K (_K0, _K1, etc).
-		for i := 0; i < 20; i++ {
+		i := 0
+		for ; i < 16; i++ {
+			f := b&c | (^b)&d
+			a5 := a<<5 | a>>(32-5)
+			b30 := b<<30 | b>>(32-30)
+			t := a5 + f + e + w[i&0xf] + _K0
+			a, b, c, d, e = t, a, b30, c, d
+		}
+		for ; i < 20; i++ {
+			tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
+			w[i&0xf] = tmp<<1 | tmp>>(32-1)
+
 			f := b&c | (^b)&d
 			a5 := a<<5 | a>>(32-5)
 			b30 := b<<30 | b>>(32-30)
-			t := a5 + f + e + w[i] + _K0
+			t := a5 + f + e + w[i&0xf] + _K0
 			a, b, c, d, e = t, a, b30, c, d
 		}
-		for i := 20; i < 40; i++ {
+		for ; i < 40; i++ {
+			tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
+			w[i&0xf] = tmp<<1 | tmp>>(32-1)
 			f := b ^ c ^ d
 			a5 := a<<5 | a>>(32-5)
 			b30 := b<<30 | b>>(32-30)
-			t := a5 + f + e + w[i] + _K1
+			t := a5 + f + e + w[i&0xf] + _K1
 			a, b, c, d, e = t, a, b30, c, d
 		}
-		for i := 40; i < 60; i++ {
-			f := b&c | b&d | c&d
+		for ; i < 60; i++ {
+			tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
+			w[i&0xf] = tmp<<1 | tmp>>(32-1)
+			f := ((b | c) & d) | (b & c)
+
 			a5 := a<<5 | a>>(32-5)
 			b30 := b<<30 | b>>(32-30)
-			t := a5 + f + e + w[i] + _K2
+			t := a5 + f + e + w[i&0xf] + _K2
 			a, b, c, d, e = t, a, b30, c, d
 		}
-		for i := 60; i < 80; i++ {
+		for ; i < 80; i++ {
+			tmp := w[(i-3)&0xf] ^ w[(i-8)&0xf] ^ w[(i-14)&0xf] ^ w[(i)&0xf]
+			w[i&0xf] = tmp<<1 | tmp>>(32-1)
 			f := b ^ c ^ d
 			a5 := a<<5 | a>>(32-5)
 			b30 := b<<30 | b>>(32-30)
-			t := a5 + f + e + w[i] + _K3
+			t := a5 + f + e + w[i&0xf] + _K3
 			a, b, c, d, e = t, a, b30, c, d
 		}