runtime: add arm soft division and modulo benchmarks

arm soft div and mod performance plays an important part
in runtime performance.

The currently implementation is very stable, but we believe
we can best it. This benchmark provides a reference point.

linux/arm omap4 pandaboard

BenchmarkUint32Div7     10000000               298 ns/op
BenchmarkUint32Div37    10000000               298 ns/op
BenchmarkUint32Div123   10000000               298 ns/op
BenchmarkUint32Div763   10000000               298 ns/op
BenchmarkUint32Div1247  10000000               299 ns/op
BenchmarkUint32Div9305  10000000               298 ns/op
BenchmarkUint32Div13307 10000000               298 ns/op
BenchmarkUint32Div52513 10000000               298 ns/op
BenchmarkUint32Div60978747      10000000               298 ns/op
BenchmarkUint32Div106956295     10000000               297 ns/op
BenchmarkUint32Mod7     10000000               280 ns/op
BenchmarkUint32Mod37    10000000               280 ns/op
BenchmarkUint32Mod123   10000000               280 ns/op
BenchmarkUint32Mod763   10000000               280 ns/op
BenchmarkUint32Mod1247  10000000               280 ns/op
BenchmarkUint32Mod9305  10000000               280 ns/op
BenchmarkUint32Mod13307 10000000               280 ns/op
BenchmarkUint32Mod52513 10000000               280 ns/op
BenchmarkUint32Mod60978747      10000000               280 ns/op
BenchmarkUint32Mod106956295     10000000               280 ns/op

R=minux.ma, rsc
CC=golang-dev
https://golang.org/cl/6258067

src/pkg/runtime/vlop_arm_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.
+
+package runtime_test
+
+import "testing"
+
+// arm soft division benchmarks adapted from 
+// http://ridiculousfish.com/files/division_benchmarks.tar.gz
+
+const numeratorsSize = 1 << 21
+
+var numerators = randomNumerators()
+
+type randstate struct {
+	hi, lo uint32
+}
+
+func (r *randstate) rand() uint32 {
+	r.hi = r.hi<<16 + r.hi>>16
+	r.hi += r.lo
+	r.lo += r.hi
+	return r.hi
+}
+
+func randomNumerators() []uint32 {
+	numerators := make([]uint32, numeratorsSize)
+	random := &randstate{2147483563, 2147483563 ^ 0x49616E42}
+	for i := range numerators {
+		numerators[i] = random.rand()
+	}
+	return numerators
+}
+
+func bmUint32Div(divisor uint32, b *testing.B) {
+	var sum uint32
+	for i := 0; i < b.N; i++ {
+		sum += numerators[i&(numeratorsSize-1)] / divisor
+	}
+}
+
+func BenchmarkUint32Div7(b *testing.B)         { bmUint32Div(7, b) }
+func BenchmarkUint32Div37(b *testing.B)        { bmUint32Div(37, b) }
+func BenchmarkUint32Div123(b *testing.B)       { bmUint32Div(123, b) }
+func BenchmarkUint32Div763(b *testing.B)       { bmUint32Div(763, b) }
+func BenchmarkUint32Div1247(b *testing.B)      { bmUint32Div(1247, b) }
+func BenchmarkUint32Div9305(b *testing.B)      { bmUint32Div(9305, b) }
+func BenchmarkUint32Div13307(b *testing.B)     { bmUint32Div(13307, b) }
+func BenchmarkUint32Div52513(b *testing.B)     { bmUint32Div(52513, b) }
+func BenchmarkUint32Div60978747(b *testing.B)  { bmUint32Div(60978747, b) }
+func BenchmarkUint32Div106956295(b *testing.B) { bmUint32Div(106956295, b) }
+
+func bmUint32Mod(divisor uint32, b *testing.B) {
+	var sum uint32
+	for i := 0; i < b.N; i++ {
+		sum += numerators[i&(numeratorsSize-1)] % divisor
+	}
+}
+
+func BenchmarkUint32Mod7(b *testing.B)         { bmUint32Mod(7, b) }
+func BenchmarkUint32Mod37(b *testing.B)        { bmUint32Mod(37, b) }
+func BenchmarkUint32Mod123(b *testing.B)       { bmUint32Mod(123, b) }
+func BenchmarkUint32Mod763(b *testing.B)       { bmUint32Mod(763, b) }
+func BenchmarkUint32Mod1247(b *testing.B)      { bmUint32Mod(1247, b) }
+func BenchmarkUint32Mod9305(b *testing.B)      { bmUint32Mod(9305, b) }
+func BenchmarkUint32Mod13307(b *testing.B)     { bmUint32Mod(13307, b) }
+func BenchmarkUint32Mod52513(b *testing.B)     { bmUint32Mod(52513, b) }
+func BenchmarkUint32Mod60978747(b *testing.B)  { bmUint32Mod(60978747, b) }
+func BenchmarkUint32Mod106956295(b *testing.B) { bmUint32Mod(106956295, b) }