examples/dot: initial version

Implements dot product in avo.

Closes #4

examples/dot/README.md

@@ -0,0 +1,3 @@
+# dot
+
+[Dot product](https://en.wikipedia.org/wiki/Dot_product) in `avo`. Ported from the [`dot_product.py` PeachPy example](https://github.com/Maratyszcza/PeachPy/blob/01d15157a973a4ae16b8046313ddab371ea582db/examples/go-generate/dot_product.py).

examples/dot/asm.go

@@ -0,0 +1,93 @@
+// +build ignore
+
+package main
+
+import (
+	. "github.com/mmcloughlin/avo/build"
+	. "github.com/mmcloughlin/avo/operand"
+	. "github.com/mmcloughlin/avo/reg"
+)
+
+var unroll = 6
+
+func main() {
+	TEXT("Dot", "func(x, y []float32) float32")
+	x := Mem{Base: Load(Param("x").Base(), GP64v())}
+	y := Mem{Base: Load(Param("y").Base(), GP64v())}
+	n := Load(Param("x").Len(), GP64v())
+
+	// Allocate accumulation registers.
+	acc := make([]VecVirtual, unroll)
+	for i := 0; i < unroll; i++ {
+		acc[i] = Yv()
+	}
+
+	// Zero initialization.
+	for i := 0; i < unroll; i++ {
+		VXORPS(acc[i], acc[i], acc[i])
+	}
+
+	// Loop over blocks and process them with vector instructions.
+	blockitems := 8 * unroll
+	blocksize := 4 * blockitems
+	LABEL("blockloop")
+	CMPQ(n, U32(blockitems))
+	JL(LabelRef("tail"))
+
+	// Load x.
+	xs := make([]VecVirtual, unroll)
+	for i := 0; i < unroll; i++ {
+		xs[i] = Yv()
+	}
+
+	for i := 0; i < unroll; i++ {
+		VMOVUPS(x.Offset(32*i), xs[i])
+	}
+
+	// The actual FMA.
+	for i := 0; i < unroll; i++ {
+		VFMADD231PS(y.Offset(32*i), xs[i], acc[i])
+	}
+
+	ADDQ(U32(blocksize), x.Base)
+	ADDQ(U32(blocksize), y.Base)
+	SUBQ(U32(blockitems), n)
+	JMP(LabelRef("blockloop"))
+
+	// Process any trailing entries.
+	LABEL("tail")
+	tail := Xv()
+	VXORPS(tail, tail, tail)
+
+	LABEL("tailloop")
+	CMPQ(n, U32(0))
+	JE(LabelRef("reduce"))
+
+	xt := Xv()
+	VMOVSS(x, xt)
+	VFMADD231SS(y, xt, tail)
+
+	ADDQ(U32(4), x.Base)
+	ADDQ(U32(4), y.Base)
+	DECQ(n)
+	JMP(LabelRef("tailloop"))
+
+	// Reduce the lanes to one.
+	LABEL("reduce")
+	for i := 1; i < unroll; i++ {
+		VADDPS(acc[0], acc[i], acc[0])
+	}
+
+	result := acc[0].AsX()
+	top := Xv()
+	VEXTRACTF128(U8(1), acc[0], top)
+	VADDPS(result, top, result)
+	VADDPS(result, tail, result)
+	VHADDPS(result, result, result)
+	VHADDPS(result, result, result)
+	Store(result, ReturnIndex(0))
+
+	RET()
+
+	Generate()
+}

examples/dot/dot.s

@@ -0,0 +1,58 @@
+// Code generated by command: go run asm.go -out dot.s -stubs stub.go. DO NOT EDIT.
+
+#include "textflag.h"
+
+// func Dot(x []float32, y []float32) float32
+TEXT ·Dot(SB), 0, $0-52
+	MOVQ	x_base(FP), AX
+	MOVQ	y_base+24(FP), CX
+	MOVQ	x_len+8(FP), DX
+	VXORPS	Y0, Y0, Y0
+	VXORPS	Y1, Y1, Y1
+	VXORPS	Y2, Y2, Y2
+	VXORPS	Y3, Y3, Y3
+	VXORPS	Y4, Y4, Y4
+	VXORPS	Y5, Y5, Y5
+blockloop:
+	CMPQ	DX, $0x00000030
+	JL	tail
+	VMOVUPS	(AX), Y6
+	VMOVUPS	32(AX), Y7
+	VMOVUPS	64(AX), Y8
+	VMOVUPS	96(AX), Y9
+	VMOVUPS	128(AX), Y10
+	VMOVUPS	160(AX), Y11
+	VFMADD231PS	(CX), Y6, Y0
+	VFMADD231PS	32(CX), Y7, Y1
+	VFMADD231PS	64(CX), Y8, Y2
+	VFMADD231PS	96(CX), Y9, Y3
+	VFMADD231PS	128(CX), Y10, Y4
+	VFMADD231PS	160(CX), Y11, Y5
+	ADDQ	$0x000000c0, AX
+	ADDQ	$0x000000c0, CX
+	SUBQ	$0x00000030, DX
+	JMP	blockloop
+tail:
+	VXORPS	X12, X12, X12
+tailloop:
+	CMPQ	DX, $0x00000000
+	JE	reduce
+	VMOVSS	(AX), X6
+	VFMADD231SS	(CX), X6, X12
+	ADDQ	$0x00000004, AX
+	ADDQ	$0x00000004, CX
+	DECQ	DX
+	JMP	tailloop
+reduce:
+	VADDPS	Y0, Y1, Y0
+	VADDPS	Y0, Y2, Y0
+	VADDPS	Y0, Y3, Y0
+	VADDPS	Y0, Y4, Y0
+	VADDPS	Y0, Y5, Y0
+	VEXTRACTF128	$0x01, Y0, X1
+	VADDPS	X0, X1, X0
+	VADDPS	X0, X12, X0
+	VHADDPS	X0, X0, X0
+	VHADDPS	X0, X0, X0
+	MOVSS	X0, ret+48(FP)
+	RET

examples/dot/dot_test.go

@@ -0,0 +1,50 @@
+package dot
+
+import (
+	"math/rand"
+	"testing"
+)
+
+//go:generate go run asm.go -out dot.s -stubs stub.go
+
+func TestEmpty(t *testing.T) {
+	if Dot(nil, nil) != 0.0 {
+		t.Fatal("expect dot product of empty vectors to be zero")
+	}
+}
+
+func TestLengths(t *testing.T) {
+	const epsilon = 0.00001
+	for n := 0; n < 1000; n++ {
+		x, y := RandomVector(n), RandomVector(n)
+		got := Dot(x, y)
+		expect := Expect(x, y)
+		relerr := got/expect - 1.0
+		if Abs(relerr) > epsilon {
+			t.Fatalf("bad result on vector length %d: got %v expect %v relative error %f", n, got, expect, relerr)
+		}
+	}
+}
+
+func Expect(x, y []float32) float32 {
+	var p float32
+	for i := range x {
+		p += x[i] * y[i]
+	}
+	return p
+}
+
+func RandomVector(n int) []float32 {
+	x := make([]float32, n)
+	for i := 0; i < n; i++ {
+		x[i] = rand.Float32() * 100
+	}
+	return x
+}
+
+func Abs(x float32) float32 {
+	if x < 0.0 {
+		return -x
+	}
+	return x
+}

examples/dot/stub.go

@@ -0,0 +1,5 @@
+// Code generated by command: go run asm.go -out dot.s -stubs stub.go. DO NOT EDIT.
+
+package dot
+
+func Dot(x []float32, y []float32) float32