add fnv1a example

examples/fnv1a/asm.go

@@ -0,0 +1,41 @@
+// +build ignore
+
+package main
+
+import (
+	. "github.com/mmcloughlin/avo/build"
+	"github.com/mmcloughlin/avo/operand"
+	"github.com/mmcloughlin/avo/reg"
+)
+
+const (
+	OffsetBasis = 0xcbf29ce484222325
+	Prime       = 0x100000001b3
+)
+
+func main() {
+	TEXT("Hash64", "func(data []byte) uint64")
+	ptr := Load(Param("data").Base(), GP64v())
+	n := Load(Param("data").Len(), GP64v())
+
+	h := reg.RAX
+	MOVQ(operand.Imm(OffsetBasis), h)
+	p := GP64v()
+	MOVQ(operand.Imm(Prime), p)
+
+	LABEL("loop")
+	CMPQ(n, operand.Imm(0))
+	JE(operand.LabelRef("done"))
+	b := GP64v()
+	MOVBQZX(operand.Mem{Base: ptr}, b)
+	XORQ(b, h)
+	MULQ(p)
+	INCQ(ptr)
+	DECQ(n)
+
+	JMP(operand.LabelRef("loop"))
+	LABEL("done")
+	Store(h, ReturnIndex(0))
+	RET()
+	Generate()
+}

examples/fnv1a/fnv1a.s

@@ -0,0 +1,21 @@
+
+#include "textflag.h"
+
+// func Hash64(data []byte) uint64
+TEXT ·Hash64(SB),0,$0-32
+	MOVQ	data_base(FP), CX
+	MOVQ	data_len+8(FP), BX
+	MOVQ	$0xcbf29ce484222325, AX
+	MOVQ	$0x100000001b3, BP
+loop:
+	CMPQ	BX, $0x0
+	JE	done
+	MOVBQZX	(CX), DX
+	XORQ	DX, AX
+	MULQ	BP
+	INCQ	CX
+	DECQ	BX
+	JMP	loop
+done:
+	MOVQ	AX, ret+24(FP)
+	RET	

examples/fnv1a/fnv_test.go

@@ -0,0 +1,20 @@
+package fnv1a
+
+import (
+	"hash/fnv"
+	"testing"
+	"testing/quick"
+)
+
+//go:generate go run asm.go -out fnv1a.s -stubs stub.go
+
+func TestHash64(t *testing.T) {
+	expect := func(data []byte) uint64 {
+		h := fnv.New64a()
+		h.Write(data)
+		return h.Sum64()
+	}
+	if err := quick.CheckEqual(Hash64, expect, nil); err != nil {
+		t.Fatal(err)
+	}
+}

examples/fnv1a/stub.go

@@ -0,0 +1,3 @@
+package fnv1a
+
+func Hash64(data []byte) uint64