Performance improvements

edwards25519/cmove.go

@@ -0,0 +1,21 @@
+// Copyright 2013 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 !amd64
+
+package edwards25519
+
+func FeCMove(f, g *FieldElement, b int32) {
+	b = -b
+	f[0] ^= b & (f[0] ^ g[0])
+	f[1] ^= b & (f[1] ^ g[1])
+	f[2] ^= b & (f[2] ^ g[2])
+	f[3] ^= b & (f[3] ^ g[3])
+	f[4] ^= b & (f[4] ^ g[4])
+	f[5] ^= b & (f[5] ^ g[5])
+	f[6] ^= b & (f[6] ^ g[6])
+	f[7] ^= b & (f[7] ^ g[7])
+	f[8] ^= b & (f[8] ^ g[8])
+	f[9] ^= b & (f[9] ^ g[9])
+}

edwards25519/cmove_amd64.s

@@ -0,0 +1,32 @@
+// Copyright 2013 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 FeCMove(f, g *FieldElement, b int32)
+TEXT ·FeCMove(SB),NOSPLIT,$0
+	MOVQ f+0(FP), AX 
+	MOVQ g+8(FP), BX 
+	MOVL b+16(FP), CX
+
+	MOVQ 0(BX),R11
+	MOVQ 8(BX),R12
+	MOVQ 16(BX),R13
+	MOVQ 24(BX),R14
+	MOVQ 32(BX),R15
+
+	MOVQ $0,DX
+	CMPQ DX, CX
+	CMOVQEQ 0(AX), R11
+	CMOVQEQ 8(AX), R12
+	CMOVQEQ 16(AX),R13
+	CMOVQEQ 24(AX),R14
+	CMOVQEQ 32(AX),R15
+
+	MOVQ R11,0(AX)
+	MOVQ R12,8(AX)
+	MOVQ R13,16(AX)
+	MOVQ R14,24(AX)
+	MOVQ R15,32(AX)
+	RET

edwards25519/cmove_decl.go

@@ -0,0 +1,14 @@
+// Copyright 2013 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 amd64
+
+package edwards25519
+
+// Replace (f,g) with (g,g) if b == 1;
+// replace (f,g) with (f,g) if b == 0.
+//
+// Preconditions: b in {0,1}.
+//go:noescape
+func FeCMove(f, g *FieldElement, b int32)

edwards25519/edwards25519.go

@@ -16,15 +16,30 @@ package edwards25519
 // context.
 type FieldElement [10]int32
 
-var zero FieldElement
-
 func FeZero(fe *FieldElement) {
-	copy(fe[:], zero[:])
+	fe[0] = 0
+	fe[1] = 0
+	fe[2] = 0
+	fe[3] = 0
+	fe[4] = 0
+	fe[5] = 0
+	fe[6] = 0
+	fe[7] = 0
+	fe[8] = 0
+	fe[9] = 0
 }
 
 func FeOne(fe *FieldElement) {
-	FeZero(fe)
 	fe[0] = 1
+	fe[1] = 0
+	fe[2] = 0
+	fe[3] = 0
+	fe[4] = 0
+	fe[5] = 0
+	fe[6] = 0
+	fe[7] = 0
+	fe[8] = 0
+	fe[9] = 0
 }
 
 func FeAdd(dst, a, b *FieldElement) {
@@ -57,24 +72,6 @@ func FeCopy(dst, src *FieldElement) {
 	copy(dst[:], src[:])
 }
 
-// Replace (f,g) with (g,g) if b == 1;
-// replace (f,g) with (f,g) if b == 0.
-//
-// Preconditions: b in {0,1}.
-func FeCMove(f, g *FieldElement, b int32) {
-	b = -b
-	f[0] ^= b & (f[0] ^ g[0])
-	f[1] ^= b & (f[1] ^ g[1])
-	f[2] ^= b & (f[2] ^ g[2])
-	f[3] ^= b & (f[3] ^ g[3])
-	f[4] ^= b & (f[4] ^ g[4])
-	f[5] ^= b & (f[5] ^ g[5])
-	f[6] ^= b & (f[6] ^ g[6])
-	f[7] ^= b & (f[7] ^ g[7])
-	f[8] ^= b & (f[8] ^ g[8])
-	f[9] ^= b & (f[9] ^ g[9])
-}
-
 func load3(in []byte) int64 {
 	var r int64
 	r = int64(in[0])