math/big: cut 2 minutes off race tests

No need to test so many sizes in race mode, especially for a package
which doesn't use goroutines.

Reduces test time from 2.5 minutes to 25 seconds.

Updates #17104

Change-Id: I7065b39273f82edece385c0d67b3f2d83d4934b8
Reviewed-on: https://go-review.googlesource.com/29163Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/math/big/arith_test.go

@@ -6,10 +6,14 @@ package big
 
 import (
 	"fmt"
+	"internal/testenv"
 	"math/rand"
+	"strings"
 	"testing"
 )
 
+var isRaceBuilder = strings.HasSuffix(testenv.Builder(), "-race")
+
 type funWW func(x, y, c Word) (z1, z0 Word)
 type argWW struct {
 	x, y, c, z1, z0 Word
@@ -123,6 +127,9 @@ var benchSizes = []int{1, 2, 3, 4, 5, 1e1, 1e2, 1e3, 1e4, 1e5}
 
 func BenchmarkAddVV(b *testing.B) {
 	for _, n := range benchSizes {
+		if isRaceBuilder && n > 1e3 {
+			continue
+		}
 		x := rndV(n)
 		y := rndV(n)
 		z := make([]Word, n)
@@ -233,6 +240,9 @@ func TestFunVW(t *testing.T) {
 
 func BenchmarkAddVW(b *testing.B) {
 	for _, n := range benchSizes {
+		if isRaceBuilder && n > 1e3 {
+			continue
+		}
 		x := rndV(n)
 		y := rndW()
 		z := make([]Word, n)
@@ -371,6 +381,9 @@ func TestMulAddWWW(t *testing.T) {
 
 func BenchmarkAddMulVVW(b *testing.B) {
 	for _, n := range benchSizes {
+		if isRaceBuilder && n > 1e3 {
+			continue
+		}
 		x := rndV(n)
 		y := rndW()
 		z := make([]Word, n)

src/math/big/gcd_test.go

@@ -20,6 +20,9 @@ func randInt(r *rand.Rand, size uint) *Int {
 }
 
 func runGCD(b *testing.B, aSize, bSize uint) {
+	if isRaceBuilder && (aSize > 1000 || bSize > 1000) {
+		b.Skip("skipping on race builder")
+	}
 	b.Run("WithoutXY", func(b *testing.B) {
 		runGCDExt(b, aSize, bSize, false)
 	})

src/math/big/int_test.go

@@ -1229,6 +1229,9 @@ func BenchmarkModSqrt224_3Mod4(b *testing.B) {
 }
 
 func BenchmarkModSqrt5430_Tonelli(b *testing.B) {
+	if isRaceBuilder {
+		b.Skip("skipping on race builder")
+	}
 	p := tri(5430)
 	x := new(Int).SetUint64(2)
 	for i := 0; i < b.N; i++ {
@@ -1238,6 +1241,9 @@ func BenchmarkModSqrt5430_Tonelli(b *testing.B) {
 }
 
 func BenchmarkModSqrt5430_3Mod4(b *testing.B) {
+	if isRaceBuilder {
+		b.Skip("skipping on race builder")
+	}
 	p := tri(5430)
 	x := new(Int).SetUint64(2)
 	for i := 0; i < b.N; i++ {

src/math/big/natconv_test.go

@@ -278,6 +278,9 @@ func BenchmarkScan(b *testing.B) {
 	const x = 10
 	for _, base := range []int{2, 8, 10, 16} {
 		for _, y := range []Word{10, 100, 1000, 10000, 100000} {
+			if isRaceBuilder && y > 1000 {
+				continue
+			}
 			b.Run(fmt.Sprintf("%d/Base%d", y, base), func(b *testing.B) {
 				b.StopTimer()
 				var z nat
@@ -301,6 +304,9 @@ func BenchmarkString(b *testing.B) {
 	const x = 10
 	for _, base := range []int{2, 8, 10, 16} {
 		for _, y := range []Word{10, 100, 1000, 10000, 100000} {
+			if isRaceBuilder && y > 1000 {
+				continue
+			}
 			b.Run(fmt.Sprintf("%d/Base%d", y, base), func(b *testing.B) {
 				b.StopTimer()
 				var z nat