crypto/sha1: add s390x assembly implementation

Use the compute intermediate message digest (KIMD) instruction
when possible. Adds test to check fallback code path in case
KIMD is not available.

Benchmark changes:
Hash8Bytes  3.4x
Hash1K      9.3x
Hash8K      10.9x

Change-Id: Ibcd71a886dfd7b3822042235b4f4eaa7a148036b
Reviewed-on: https://go-review.googlesource.com/22350
Run-TryBot: Michael Munday <munday@ca.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/crypto/sha1/fallback_test.go

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build s390x
+
+package sha1
+
+import (
+	"fmt"
+	"io"
+	"testing"
+)
+
+// Tests the fallback code path in case the optimized asm
+// implementation cannot be used.
+// See also TestBlockGeneric.
+func TestGenericPath(t *testing.T) {
+	if useAsm == false {
+		t.Skipf("assembly implementation unavailable")
+	}
+	useAsm = false
+	defer func() { useAsm = true }()
+	c := New()
+	in := "ΑΒΓΔΕϜΖΗΘΙΚΛΜΝΞΟΠϺϘΡΣΤΥΦΧΨΩ"
+	gold := "0f58c2bb130f8182375f325c18342215255387e5"
+	if _, err := io.WriteString(c, in); err != nil {
+		t.Fatalf("could not write to c: %v", err)
+	}
+	out := fmt.Sprintf("%x", c.Sum(nil))
+	if out != gold {
+		t.Fatalf("mismatch: got %s, wanted %s", out, gold)
+	}
+}

src/crypto/sha1/sha1_test.go

@@ -91,7 +91,7 @@ func TestBlockSize(t *testing.T) {
 	}
 }
 
-// Tests that blockGeneric (pure Go) and block (in assembly for amd64, 386, arm) match.
+// Tests that blockGeneric (pure Go) and block (in assembly for some architectures) match.
 func TestBlockGeneric(t *testing.T) {
 	gen, asm := New().(*digest), New().(*digest)
 	buf := make([]byte, BlockSize*20) // arbitrary factor

src/crypto/sha1/sha1block_decl.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build amd64 amd64p32 arm 386
+// +build amd64 amd64p32 arm 386 s390x
 
 package sha1
 

src/crypto/sha1/sha1block_generic.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64,!amd64p32,!386,!arm
+// +build !amd64,!amd64p32,!386,!arm,!s390x
 
 package sha1
 

src/crypto/sha1/sha1block_s390x.go

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sha1
+
+// featureCheck reports whether the CPU supports the
+// SHA1 compute intermediate message digest (KIMD)
+// function code.
+func featureCheck() bool
+
+var useAsm = featureCheck()

src/crypto/sha1/sha1block_s390x.s

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "textflag.h"
+
+// func featureCheck() bool
+TEXT ·featureCheck(SB),NOSPLIT,$16-1
+	LA	tmp-16(SP), R1
+	XOR	R0, R0         // query function code is 0
+	WORD    $0xB93E0006    // KIMD (R6 is ignored)
+	MOVBZ	tmp-16(SP), R4 // get the first byte
+	AND	$0x40, R4      // bit 1 (big endian) for SHA1
+	CMPBEQ	R4, $0, nosha1
+	MOVB	$1, ret+0(FP)
+	RET
+nosha1:
+	MOVB	$0, ret+0(FP)
+	RET
+
+// func block(dig *digest, p []byte)
+TEXT ·block(SB),NOSPLIT,$0-32
+	MOVBZ	·useAsm(SB), R4
+	LMG	dig+0(FP), R1, R3 // R2 = &p[0], R3 = len(p)
+	CMPBNE	R4, $1, generic
+	MOVBZ	$1, R0        // SHA1 function code
+loop:
+	WORD	$0xB93E0002   // KIMD R2
+	BVS	loop          // continue if interrupted
+done:
+	XOR	R0, R0        // restore R0
+	RET
+generic:
+	BR	·blockGeneric(SB)