test/bench/go1: add mandelbrot for floating point

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6244063

test/bench/go1/mandel_test.go

+// Copyright 2012 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.
+
+// This benchmark, taken from the shootuot, tests floating point performance.
+
+package go1
+
+import "testing"
+
+func mandelbrot(n int) int {
+	const Iter = 50
+	const Zero float64 = 0
+	const Limit = 2.0
+	ok := 0
+	for y := 0; y < n; y++ {
+		for x := 0; x < n; x++ {
+			Zr, Zi, Tr, Ti := Zero, Zero, Zero, Zero
+			Cr := (2*float64(x)/float64(n) - 1.5)
+			Ci := (2*float64(y)/float64(n) - 1.0)
+
+			for i := 0; i < Iter && (Tr+Ti <= Limit*Limit); i++ {
+				Zi = 2*Zr*Zi + Ci
+				Zr = Tr - Ti + Cr
+				Tr = Zr * Zr
+				Ti = Zi * Zi
+			}
+
+			if Tr+Ti <= Limit*Limit {
+				ok++
+			}
+		}
+	}
+	return ok
+}
+
+func BenchmarkMandelbrot200(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		mandelbrot(200)
+	}
+}