math/big: more Float conversion tests

Change-Id: Ia30886569141ca2e0321bea6ee1d5c9e0f79d6f9
Reviewed-on: https://go-review.googlesource.com/3941Reviewed-by: Alan Donovan <adonovan@google.com>

src/math/big/floatconv_test.go

@@ -5,6 +5,7 @@
 package big
 
 import (
+	"io"
 	"math"
 	"strconv"
 	"testing"
@@ -167,7 +168,7 @@ func TestFloat64Format(t *testing.T) {
 
 		{below1e23, 'e', 17, "9.99999999999999748e+22"},
 		{below1e23, 'f', 17, "99999999999999974834176.00000000000000000"},
-		// {below1e23, 'g', 17, "9.9999999999999975e+22"},
+		{below1e23, 'g', 17, "9.9999999999999975e+22"},
 
 		// {below1e23, 'e', -1, "9.999999999999997e+22"},
 		// {below1e23, 'f', -1, "99999999999999970000000"},
@@ -236,3 +237,91 @@ func TestFloat64Format(t *testing.T) {
 		}
 	}
 }
+
+func TestFloatFormat(t *testing.T) {
+	for _, test := range []struct {
+		x      string
+		format byte
+		prec   int
+		want   string
+	}{
+		{"0", 'f', 0, "0"},
+		{"-0", 'f', 0, "-0"},
+		{"1", 'f', 0, "1"},
+		{"-1", 'f', 0, "-1"},
+
+		{"1.459", 'e', 0, "1e+00"},
+		{"2.459", 'e', 1, "2.5e+00"},
+		{"3.459", 'e', 2, "3.46e+00"},
+		{"4.459", 'e', 3, "4.459e+00"},
+		{"5.459", 'e', 4, "5.4590e+00"},
+
+		{"1.459", 'E', 0, "1E+00"},
+		{"2.459", 'E', 1, "2.5E+00"},
+		{"3.459", 'E', 2, "3.46E+00"},
+		{"4.459", 'E', 3, "4.459E+00"},
+		{"5.459", 'E', 4, "5.4590E+00"},
+
+		{"1.459", 'f', 0, "1"},
+		{"2.459", 'f', 1, "2.5"},
+		{"3.459", 'f', 2, "3.46"},
+		{"4.459", 'f', 3, "4.459"},
+		{"5.459", 'f', 4, "5.4590"},
+
+		{"1.459", 'g', 0, "1"},
+		{"2.459", 'g', 1, "2"},
+		{"3.459", 'g', 2, "3.5"},
+		{"4.459", 'g', 3, "4.46"},
+		{"5.459", 'g', 4, "5.459"},
+
+		{"1459", 'g', 0, "1e+03"},
+		{"2459", 'g', 1, "2e+03"},
+		{"3459", 'g', 2, "3.5e+03"},
+		{"4459", 'g', 3, "4.46e+03"},
+		{"5459", 'g', 4, "5459"},
+
+		{"1459", 'G', 0, "1E+03"},
+		{"2459", 'G', 1, "2E+03"},
+		{"3459", 'G', 2, "3.5E+03"},
+		{"4459", 'G', 3, "4.46E+03"},
+		{"5459", 'G', 4, "5459"},
+
+		{"3", 'e', 40, "3.0000000000000000000000000000000000000000e+00"},
+		{"3", 'f', 40, "3.0000000000000000000000000000000000000000"},
+		{"3", 'g', 40, "3"},
+
+		{"3e40", 'e', 40, "3.0000000000000000000000000000000000000000e+40"},
+		{"3e40", 'f', 4, "30000000000000000000000000000000000000000.0000"},
+		{"3e40", 'g', 40, "3e+40"},
+
+		// TODO(gri) need tests for actual large Floats
+
+		// These depend on the selected mantissa length to match strconv.FormatFloat.
+		// Disabled for now.
+		// {"0", 'b', 0, "0"},
+		// {"-0", 'b', 0, "-0"},
+		// {"1.0", 'b', 0, "4503599627370496p-52"},
+		// {"-1.0", 'b', 0, "-4503599627370496p-52"},
+		// {"4503599627370496", 'b', 0, "4503599627370496p+0"},
+
+		{"0", 'p', 0, "0"},
+		{"-0", 'p', 0, "-0"},
+		{"1024.0", 'p', 0, "0x.8p11"},
+		{"-1024.0", 'p', 0, "-0x.8p11"},
+
+		// unsupported format
+		{"3.14", 'x', 0, "%x"},
+	} {
+		f, _, err := ParseFloat(test.x, 0, 1000, ToNearestEven)
+		// TODO(gri) should we return io.EOF at the end?
+		if err != nil && err != io.EOF {
+			t.Errorf("%v: %s", test, err)
+			continue
+		}
+
+		got := f.Format(test.format, test.prec)
+		if got != test.want {
+			t.Errorf("%v: got %s; want %s", test, got, test.want)
+		}
+	}
+}