math/big: remove (*Float).Scan, ScanFloat; more robust (*Float).Parse

- (*Float).Scan conflicted with fmt.Scanner.Scan; it was also only used
  internally. Removed it, as well as the companion ScanFloat function.

- (*Float).Parse (and thus ParseFloat) can now also parse infinities.
  As a result, more code could be simplified.

- Fixed a bug in rounding (round may implicitly be called for infinite
  values). Found via existing test cases, after simplifying some code.

- Added more test cases.

Fixes issue #10938.

Change-Id: I1df97821654f034965ba8b82b272e52e6dc427f1
Reviewed-on: https://go-review.googlesource.com/10498
Reviewed-by: Alan Donovan <adonovan@google.com>

1 files changed, 32 insertions, 2 deletions

diff --git a/src/math/big/floatconv_test.go b/src/math/big/floatconv_test.go
index fffcd70ce6..656d28c975 100644
--- a/src/math/big/floatconv_test.go
+++ b/src/math/big/floatconv_test.go
@@ -11,9 +11,12 @@ import (
 )
 
 func TestFloatSetFloat64String(t *testing.T) {
+	inf := math.Inf(0)
+	nan := math.NaN()
+
 	for _, test := range []struct {
 		s string
-		x float64
+		x float64 // NaNs represent invalid inputs
 	}{
 		// basics
 		{"0", 0},
@@ -45,6 +48,25 @@ func TestFloatSetFloat64String(t *testing.T) {
 		{"1.E+10", 1e10},
 		{"+1E-10", 1e-10},
 
+		// infinities
+		{"Inf", inf},
+		{"+Inf", inf},
+		{"-Inf", -inf},
+		{"inf", inf},
+		{"+inf", inf},
+		{"-inf", -inf},
+
+		// invalid numbers
+		{"", nan},
+		{"-", nan},
+		{"0x", nan},
+		{"0e", nan},
+		{"1.2ef", nan},
+		{"2..3", nan},
+		{"123..", nan},
+		{"infinity", nan},
+		{"foobar", nan},
+
 		// misc decimal values
 		{"3.14159265", 3.14159265},
 		{"-687436.79457e-245", -687436.79457e-245},
@@ -96,8 +118,16 @@ func TestFloatSetFloat64String(t *testing.T) {
 		var x Float
 		x.SetPrec(53)
 		_, ok := x.SetString(test.s)
+		if math.IsNaN(test.x) {
+			// test.s is invalid
+			if ok {
+				t.Errorf("%s: want parse error", test.s)
+			}
+			continue
+		}
+		// test.s is valid
 		if !ok {
-			t.Errorf("%s: parse error", test.s)
+			t.Errorf("%s: got parse error", test.s)
 			continue
 		}
 		f, _ := x.Float64()