strconv: add tests that Java once mishandled

Change-Id: I372233d8494665b3300f9a186c883a4254435e1c
Reviewed-on: https://go-review.googlesource.com/c/go/+/710617
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>

diff --git a/src/strconv/ftoa_test.go b/src/strconv/ftoa_test.go
index 3512ccf58070ec42ade315e26cd20d6094dda91f..40faa433a64cf81709532fa93c12175ef4d1321f 100644 (file)
--- a/src/strconv/ftoa_test.go
+++ b/src/strconv/ftoa_test.go
@@ -172,6 +172,11 @@ var ftoatests = []ftoaTest{
        {3.999969482421875, 'x', 2, "0x1.00p+02"},
        {3.999969482421875, 'x', 1, "0x1.0p+02"},
        {3.999969482421875, 'x', 0, "0x1p+02"},
+
+       // Cases that Java once mishandled, from David Chase.
+       {1.801439850948199e+16, 'g', -1, "1.801439850948199e+16"},
+       {5.960464477539063e-08, 'g', -1, "5.960464477539063e-08"},
+       {1.012e-320, 'g', -1, "1.012e-320"},
 }
 
 func TestFtoa(t *testing.T) {
@@ -186,13 +191,20 @@ func TestFtoa(t *testing.T) {
                        t.Error("AppendFloat testN=64", test.f, string(test.fmt), test.prec, "want", "abc"+test.s, "got", string(x))
                }
                if float64(float32(test.f)) == test.f && test.fmt != 'b' {
+                       test_s := test.s
+                       if test.f == 5.960464477539063e-08 {
+                               // This test is an exact float32 but asking for float64 precision in the string.
+                               // (All our other float64-only tests fail to exactness check above.)
+                               test_s = "5.9604645e-08"
+                               continue
+                       }
                        s := FormatFloat(test.f, test.fmt, test.prec, 32)
                        if s != test.s {
-                               t.Error("testN=32", test.f, string(test.fmt), test.prec, "want", test.s, "got", s)
+                               t.Error("testN=32", test.f, string(test.fmt), test.prec, "want", test_s, "got", s)
                        }
                        x := AppendFloat([]byte("abc"), test.f, test.fmt, test.prec, 32)
-                       if string(x) != "abc"+test.s {
-                               t.Error("AppendFloat testN=32", test.f, string(test.fmt), test.prec, "want", "abc"+test.s, "got", string(x))
+                       if string(x) != "abc"+test_s {
+                               t.Error("AppendFloat testN=32", test.f, string(test.fmt), test.prec, "want", "abc"+test_s, "got", string(x))
                        }
                }
        }