diff --git a/vector/acc_amd64.s b/vector/acc_amd64.s
index 7ef7aac..c74b2a9 100644
--- a/vector/acc_amd64.s
+++ b/vector/acc_amd64.s
@@ -1,6 +1,4 @@
-// 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.
+// generated by go run gen.go; DO NOT EDIT
 
 // +build !appengine
 // +build gc
@@ -12,8 +10,8 @@
 
 DATA flAlmost256<>+0x00(SB)/8, $0x437fffff437fffff
 DATA flAlmost256<>+0x08(SB)/8, $0x437fffff437fffff
-DATA flOnes<>+0x00(SB)/8, $0x3f8000003f800000
-DATA flOnes<>+0x08(SB)/8, $0x3f8000003f800000
+DATA flOne<>+0x00(SB)/8, $0x3f8000003f800000
+DATA flOne<>+0x08(SB)/8, $0x3f8000003f800000
 DATA flSignMask<>+0x00(SB)/8, $0x7fffffff7fffffff
 DATA flSignMask<>+0x08(SB)/8, $0x7fffffff7fffffff
 DATA shuffleMask<>+0x00(SB)/8, $0x0c0804000c080400
@@ -22,7 +20,7 @@ DATA fxAlmost256<>+0x00(SB)/8, $0x000000ff000000ff
 DATA fxAlmost256<>+0x08(SB)/8, $0x000000ff000000ff
 
 GLOBL flAlmost256<>(SB), (NOPTR+RODATA), $16
-GLOBL flOnes<>(SB), (NOPTR+RODATA), $16
+GLOBL flOne<>(SB), (NOPTR+RODATA), $16
 GLOBL flSignMask<>(SB), (NOPTR+RODATA), $16
 GLOBL shuffleMask<>(SB), (NOPTR+RODATA), $16
 GLOBL fxAlmost256<>(SB), (NOPTR+RODATA), $16
@@ -67,9 +65,10 @@ TEXT ·fixedAccumulateOpSrcSIMD(SB), NOSPLIT, $0-48
 	ANDQ $-4, CX
 
 	// fxAlmost256 := XMM(0x000000ff repeated four times) // Maximum of an uint8.
+	MOVOU fxAlmost256<>(SB), X5
+
 	// shuffleMask := XMM(0x0c080400 repeated four times) // PSHUFB shuffle mask.
 	// offset      := XMM(0x00000000 repeated four times) // Cumulative sum.
-	MOVOU fxAlmost256<>(SB), X5
 	MOVOU shuffleMask<>(SB), X6
 	XORPS X7, X7
 
@@ -117,7 +116,10 @@ fxAccOpSrcLoop4:
 	BYTE $0x66; BYTE $0x0f; BYTE $0x72; BYTE $0xd2; BYTE $0x0c
 	BYTE $0x66; BYTE $0x0f; BYTE $0x38; BYTE $0x3b; BYTE $0xd5
 
-	// z = shuffleTheLowBytesOfEach4ByteElement(y)
+	// z = convertToInt32(y)
+	// No-op.
+
+	// z = shuffleTheLowBytesOfEach4ByteElement(z)
 	// copy(dst[:4], low4BytesOf(z))
 	PSHUFB X6, X2
 	MOVL   X2, (DI)
@@ -137,7 +139,7 @@ fxAccOpSrcLoop4:
 fxAccOpSrcLoop1:
 	// for i < len(src)
 	CMPQ AX, DX
-	JAE  fxAccOpSrcEnd
+	JAE  fxAccOpSrcCleanup
 
 	// x = src[i] + offset
 	MOVL  (SI), X1
@@ -158,7 +160,10 @@ fxAccOpSrcLoop1:
 	BYTE $0x66; BYTE $0x0f; BYTE $0x72; BYTE $0xd2; BYTE $0x0c
 	BYTE $0x66; BYTE $0x0f; BYTE $0x38; BYTE $0x3b; BYTE $0xd5
 
-	// dst[0] = uint8(y)
+	// z = convertToInt32(y)
+	// No-op.
+
+	// dst[0] = uint8(z)
 	MOVL X2, BX
 	MOVB BX, (DI)
 
@@ -173,6 +178,9 @@ fxAccOpSrcLoop1:
 	ADDQ $4, SI
 	JMP  fxAccOpSrcLoop1
 
+fxAccOpSrcCleanup:
+	// No-op.
+
 fxAccOpSrcEnd:
 	RET
 
@@ -187,7 +195,7 @@ fxAccOpSrcEnd:
 //	xmm1	x
 //	xmm2	y, z
 //	xmm3	flAlmost256
-//	xmm4	flOnes
+//	xmm4	flOne
 //	xmm5	flSignMask
 //	xmm6	shuffleMask
 //	xmm7	offset
@@ -214,13 +222,14 @@ TEXT ·floatingAccumulateOpSrcSIMD(SB), NOSPLIT, $8-48
 	LDMXCSR mxcsrNew-4(SP)
 
 	// flAlmost256 := XMM(0x437fffff repeated four times) // 255.99998 as a float32.
-	// flOnes      := XMM(0x3f800000 repeated four times) // 1 as a float32.
+	// flOne       := XMM(0x3f800000 repeated four times) // 1 as a float32.
 	// flSignMask  := XMM(0x7fffffff repeated four times) // All but the sign bit of a float32.
+	MOVOU flAlmost256<>(SB), X3
+	MOVOU flOne<>(SB), X4
+	MOVOU flSignMask<>(SB), X5
+
 	// shuffleMask := XMM(0x0c080400 repeated four times) // PSHUFB shuffle mask.
 	// offset      := XMM(0x00000000 repeated four times) // Cumulative sum.
-	MOVOU flAlmost256<>(SB), X3
-	MOVOU flOnes<>(SB), X4
-	MOVOU flSignMask<>(SB), X5
 	MOVOU shuffleMask<>(SB), X6
 	XORPS X7, X7
 
@@ -254,19 +263,20 @@ flAccOpSrcLoop4:
 	ADDPS X7, X1
 
 	// y = x & flSignMask
-	// y = min(y, flOnes)
+	// y = min(y, flOne)
 	// y = mul(y, flAlmost256)
 	MOVOU X5, X2
 	ANDPS X1, X2
 	MINPS X4, X2
 	MULPS X3, X2
 
-	// z = float32ToInt32(y)
+	// z = convertToInt32(y)
+	CVTPS2PL X2, X2
+
 	// z = shuffleTheLowBytesOfEach4ByteElement(z)
 	// copy(dst[:4], low4BytesOf(z))
-	CVTPS2PL X2, X2
-	PSHUFB   X6, X2
-	MOVL     X2, (DI)
+	PSHUFB X6, X2
+	MOVL   X2, (DI)
 
 	// offset = XMM(x@3, x@3, x@3, x@3)
 	MOVOU  X1, X7
@@ -283,25 +293,26 @@ flAccOpSrcLoop4:
 flAccOpSrcLoop1:
 	// for i < len(src)
 	CMPQ AX, DX
-	JAE  flAccOpSrcRestoreMXCSR
+	JAE  flAccOpSrcCleanup
 
 	// x = src[i] + offset
 	MOVL  (SI), X1
 	ADDPS X7, X1
 
 	// y = x & flSignMask
-	// y = min(y, flOnes)
+	// y = min(y, flOne)
 	// y = mul(y, flAlmost256)
 	MOVOU X5, X2
 	ANDPS X1, X2
 	MINPS X4, X2
 	MULPS X3, X2
 
-	// z = float32ToInt32(y)
-	// dst[0] = uint8(z)
+	// z = convertToInt32(y)
 	CVTPS2PL X2, X2
-	MOVL     X2, BX
-	MOVB     BX, (DI)
+
+	// dst[0] = uint8(z)
+	MOVL X2, BX
+	MOVB BX, (DI)
 
 	// offset = x
 	MOVOU X1, X7
@@ -314,7 +325,7 @@ flAccOpSrcLoop1:
 	ADDQ $4, SI
 	JMP  flAccOpSrcLoop1
 
-flAccOpSrcRestoreMXCSR:
+flAccOpSrcCleanup:
 	LDMXCSR mxcsrOrig-8(SP)
 
 flAccOpSrcEnd:
diff --git a/vector/gen.go b/vector/gen.go
new file mode 100644
index 0000000..482e8f6
--- /dev/null
+++ b/vector/gen.go
@@ -0,0 +1,178 @@
+// 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 ignore
+
+package main
+
+import (
+	"bytes"
+	"io/ioutil"
+	"log"
+	"text/template"
+)
+
+const (
+	copyright = "" +
+		"// Copyright 2016 The Go Authors. All rights reserved.\n" +
+		"// Use of this source code is governed by a BSD-style\n" +
+		"// license that can be found in the LICENSE file.\n"
+
+	doNotEdit = "// generated by go run gen.go; DO NOT EDIT\n"
+
+	dashDashDash = "// --------"
+)
+
+func main() {
+	tmpl, err := ioutil.ReadFile("gen_acc_amd64.s.tmpl")
+	if err != nil {
+		log.Fatalf("ReadFile: %v", err)
+	}
+	if !bytes.HasPrefix(tmpl, []byte(copyright)) {
+		log.Fatal("source template did not start with the copyright header")
+	}
+	tmpl = tmpl[len(copyright):]
+
+	preamble := []byte(nil)
+	if i := bytes.Index(tmpl, []byte(dashDashDash)); i < 0 {
+		log.Fatalf("source template did not contain %q", dashDashDash)
+	} else {
+		preamble, tmpl = tmpl[:i], tmpl[i:]
+	}
+
+	t, err := template.New("").Parse(string(tmpl))
+	if err != nil {
+		log.Fatalf("Parse: %v", err)
+	}
+
+	out := bytes.NewBuffer(nil)
+	out.WriteString(doNotEdit)
+	out.Write(preamble)
+
+	for i, v := range instances {
+		if i != 0 {
+			out.WriteString("\n")
+		}
+		if err := t.Execute(out, v); err != nil {
+			log.Fatalf("Execute(%q): %v", v.ShortName, err)
+		}
+	}
+
+	if err := ioutil.WriteFile("acc_amd64.s", out.Bytes(), 0666); err != nil {
+		log.Fatalf("WriteFile: %v", err)
+	}
+}
+
+var instances = []struct {
+	LongName       string
+	ShortName      string
+	FrameSize      string
+	SrcType        string
+	XMM3           string
+	XMM4           string
+	XMM5           string
+	Setup          string
+	Cleanup        string
+	Add            string
+	ClampAndScale  string
+	ConvertToInt32 string
+}{{
+	LongName:       "fixedAccumulateOpSrc",
+	ShortName:      "fxAccOpSrc",
+	FrameSize:      fxFrameSize,
+	SrcType:        fxSrcType,
+	XMM3:           fxXMM3,
+	XMM4:           fxXMM4,
+	XMM5:           fxXMM5,
+	Setup:          fxSetup,
+	Cleanup:        fxCleanup,
+	Add:            fxAdd,
+	ClampAndScale:  fxClampAndScale,
+	ConvertToInt32: fxConvertToInt32,
+}, {
+	LongName:       "floatingAccumulateOpSrc",
+	ShortName:      "flAccOpSrc",
+	FrameSize:      flFrameSize,
+	SrcType:        flSrcType,
+	XMM3:           flXMM3,
+	XMM4:           flXMM4,
+	XMM5:           flXMM5,
+	Setup:          flSetup,
+	Cleanup:        flCleanup,
+	Add:            flAdd,
+	ClampAndScale:  flClampAndScale,
+	ConvertToInt32: flConvertToInt32,
+}}
+
+const (
+	fxFrameSize = `0`
+	flFrameSize = `8`
+
+	fxSrcType = `[]uint32`
+	flSrcType = `[]float32`
+
+	fxXMM3 = `-`
+	flXMM3 = `flAlmost256`
+
+	fxXMM4 = `-`
+	flXMM4 = `flOne`
+
+	fxXMM5 = `fxAlmost256`
+	flXMM5 = `flSignMask`
+
+	fxSetup = `
+		// fxAlmost256 := XMM(0x000000ff repeated four times) // Maximum of an uint8.
+		MOVOU fxAlmost256<>(SB), X5
+		`
+	flSetup = `
+		// Set MXCSR bits 13 and 14, so that the CVTPS2PL below is "Round To Zero".
+		STMXCSR mxcsrOrig-8(SP)
+		MOVL    mxcsrOrig-8(SP), AX
+		ORL     $0x6000, AX
+		MOVL    AX, mxcsrNew-4(SP)
+		LDMXCSR mxcsrNew-4(SP)
+
+		// flAlmost256 := XMM(0x437fffff repeated four times) // 255.99998 as a float32.
+		// flOne       := XMM(0x3f800000 repeated four times) // 1 as a float32.
+		// flSignMask  := XMM(0x7fffffff repeated four times) // All but the sign bit of a float32.
+		MOVOU flAlmost256<>(SB), X3
+		MOVOU flOne<>(SB), X4
+		MOVOU flSignMask<>(SB), X5
+		`
+
+	fxCleanup = `// No-op.`
+	flCleanup = `LDMXCSR mxcsrOrig-8(SP)`
+
+	fxAdd = `PADDD`
+	flAdd = `ADDPS`
+
+	fxClampAndScale = `
+		// y = abs(x)
+		// y >>= 12 // Shift by 2*ϕ - 8.
+		// y = min(y, fxAlmost256)
+		//
+		// pabsd  %xmm1,%xmm2
+		// psrld  $0xc,%xmm2
+		// pminud %xmm5,%xmm2
+		//
+		// Hopefully we'll get these opcode mnemonics into the assembler for Go
+		// 1.8. https://golang.org/issue/16007 isn't exactly the same thing, but
+		// it's similar.
+		BYTE $0x66; BYTE $0x0f; BYTE $0x38; BYTE $0x1e; BYTE $0xd1
+		BYTE $0x66; BYTE $0x0f; BYTE $0x72; BYTE $0xd2; BYTE $0x0c
+		BYTE $0x66; BYTE $0x0f; BYTE $0x38; BYTE $0x3b; BYTE $0xd5
+		`
+	flClampAndScale = `
+		// y = x & flSignMask
+		// y = min(y, flOne)
+		// y = mul(y, flAlmost256)
+		MOVOU X5, X2
+		ANDPS X1, X2
+		MINPS X4, X2
+		MULPS X3, X2
+		`
+
+	fxConvertToInt32 = `// No-op.`
+	flConvertToInt32 = `CVTPS2PL X2, X2`
+)
diff --git a/vector/gen_acc_amd64.s.tmpl b/vector/gen_acc_amd64.s.tmpl
new file mode 100644
index 0000000..854abe5
--- /dev/null
+++ b/vector/gen_acc_amd64.s.tmpl
@@ -0,0 +1,160 @@
+// 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 !appengine
+// +build gc
+// +build !noasm
+
+#include "textflag.h"
+
+// fl is short for floating point math. fx is short for fixed point math.
+
+DATA flAlmost256<>+0x00(SB)/8, $0x437fffff437fffff
+DATA flAlmost256<>+0x08(SB)/8, $0x437fffff437fffff
+DATA flOne<>+0x00(SB)/8, $0x3f8000003f800000
+DATA flOne<>+0x08(SB)/8, $0x3f8000003f800000
+DATA flSignMask<>+0x00(SB)/8, $0x7fffffff7fffffff
+DATA flSignMask<>+0x08(SB)/8, $0x7fffffff7fffffff
+DATA shuffleMask<>+0x00(SB)/8, $0x0c0804000c080400
+DATA shuffleMask<>+0x08(SB)/8, $0x0c0804000c080400
+DATA fxAlmost256<>+0x00(SB)/8, $0x000000ff000000ff
+DATA fxAlmost256<>+0x08(SB)/8, $0x000000ff000000ff
+
+GLOBL flAlmost256<>(SB), (NOPTR+RODATA), $16
+GLOBL flOne<>(SB), (NOPTR+RODATA), $16
+GLOBL flSignMask<>(SB), (NOPTR+RODATA), $16
+GLOBL shuffleMask<>(SB), (NOPTR+RODATA), $16
+GLOBL fxAlmost256<>(SB), (NOPTR+RODATA), $16
+
+// func haveSSE4_1() bool
+TEXT ·haveSSE4_1(SB), NOSPLIT, $0
+	MOVQ $1, AX
+	CPUID
+	SHRQ $19, CX
+	ANDQ $1, CX
+	MOVB CX, ret+0(FP)
+	RET
+
+// ----------------------------------------------------------------------------
+
+// func {{.LongName}}SIMD(dst []uint8, src {{.SrcType}})
+//
+// XMM registers. Variable names are per
+// https://github.com/google/font-rs/blob/master/src/accumulate.c
+//
+//	xmm0	scratch
+//	xmm1	x
+//	xmm2	y, z
+//	xmm3	{{.XMM3}}
+//	xmm4	{{.XMM4}}
+//	xmm5	{{.XMM5}}
+//	xmm6	shuffleMask
+//	xmm7	offset
+TEXT ·{{.LongName}}SIMD(SB), NOSPLIT, ${{.FrameSize}}-48
+	MOVQ dst_base+0(FP), DI
+	MOVQ dst_len+8(FP), BX
+	MOVQ src_base+24(FP), SI
+	MOVQ src_len+32(FP), CX
+
+	// Sanity check that len(dst) >= len(src).
+	CMPQ BX, CX
+	JLT  {{.ShortName}}End
+
+	// CX = len(src) &^ 3
+	// DX = len(src)
+	MOVQ CX, DX
+	ANDQ $-4, CX
+
+	{{.Setup}}
+
+	// shuffleMask := XMM(0x0c080400 repeated four times) // PSHUFB shuffle mask.
+	// offset      := XMM(0x00000000 repeated four times) // Cumulative sum.
+	MOVOU shuffleMask<>(SB), X6
+	XORPS X7, X7
+
+	// i := 0
+	MOVQ $0, AX
+
+{{.ShortName}}Loop4:
+	// for i < (len(src) &^ 3)
+	CMPQ AX, CX
+	JAE  {{.ShortName}}Loop1
+
+	// x = XMM(s0, s1, s2, s3)
+	//
+	// Where s0 is src[i+0], s1 is src[i+1], etc.
+	MOVOU (SI), X1
+
+	// scratch = XMM(0, s0, s1, s2)
+	// x += scratch                                  // yields x == XMM(s0, s0+s1, s1+s2, s2+s3)
+	MOVOU    X1, X0
+	PSLLO    $4, X0
+	{{.Add}} X0, X1
+
+	// scratch = XMM(0, 0, 0, 0)
+	// scratch = XMM(scratch@0, scratch@0, x@0, x@1) // yields scratch == XMM(0, 0, s0, s0+s1)
+	// x += scratch                                  // yields x == XMM(s0, s0+s1, s0+s1+s2, s0+s1+s2+s3)
+	XORPS    X0, X0
+	SHUFPS   $0x40, X1, X0
+	{{.Add}} X0, X1
+
+	// x += offset
+	{{.Add}} X7, X1
+
+	{{.ClampAndScale}}
+
+	// z = convertToInt32(y)
+	{{.ConvertToInt32}}
+
+	// z = shuffleTheLowBytesOfEach4ByteElement(z)
+	// copy(dst[:4], low4BytesOf(z))
+	PSHUFB X6, X2
+	MOVL   X2, (DI)
+
+	// offset = XMM(x@3, x@3, x@3, x@3)
+	MOVOU  X1, X7
+	SHUFPS $0xff, X1, X7
+
+	// i += 4
+	// dst = dst[4:]
+	// src = src[4:]
+	ADDQ $4, AX
+	ADDQ $4, DI
+	ADDQ $16, SI
+	JMP  {{.ShortName}}Loop4
+
+{{.ShortName}}Loop1:
+	// for i < len(src)
+	CMPQ AX, DX
+	JAE  {{.ShortName}}Cleanup
+
+	// x = src[i] + offset
+	MOVL     (SI), X1
+	{{.Add}} X7, X1
+
+	{{.ClampAndScale}}
+
+	// z = convertToInt32(y)
+	{{.ConvertToInt32}}
+
+	// dst[0] = uint8(z)
+	MOVL X2, BX
+	MOVB BX, (DI)
+
+	// offset = x
+	MOVOU X1, X7
+
+	// i += 1
+	// dst = dst[1:]
+	// src = src[1:]
+	ADDQ $1, AX
+	ADDQ $1, DI
+	ADDQ $4, SI
+	JMP  {{.ShortName}}Loop1
+
+{{.ShortName}}Cleanup:
+	{{.Cleanup}}
+
+{{.ShortName}}End:
+	RET
diff --git a/vector/vector.go b/vector/vector.go
index a9f832a..aed62d2 100644
--- a/vector/vector.go
+++ b/vector/vector.go
@@ -2,6 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:generate go run gen.go
+//go:generate asmfmt -w acc_amd64.s
+
+// asmfmt is https://github.com/klauspost/asmfmt
+
 // Package vector provides a rasterizer for 2-D vector graphics.
 package vector // import "golang.org/x/image/vector"