examples/dot: initial version

Implements dot product in avo.

Closes #4

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
+}