1 files changed, 60 insertions, 0 deletions
diff --git a/test/fixedbugs/bug120.go b/test/fixedbugs/bug120.go
new file mode 100644
index 0000000..58355e5
--- /dev/null
+++ b/test/fixedbugs/bug120.go
@@ -0,0 +1,60 @@
+// run
+
+// Copyright 2009 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 main
+
+import "os"
+import "strconv"
+
+type Test struct {
+	f   float64
+	in  string
+	out string
+}
+
+var tests = []Test{
+	Test{123.5, "123.5", "123.5"},
+	Test{456.7, "456.7", "456.7"},
+	Test{1e23 + 8.5e6, "1e23+8.5e6", "1.0000000000000001e+23"},
+	Test{100000000000000008388608, "100000000000000008388608", "1.0000000000000001e+23"},
+	Test{1e23 + 8388609, "1e23+8388609", "1.0000000000000001e+23"},
+
+	// "x" = the floating point value from converting the string x.
+	// These are exactly representable in 64-bit floating point:
+	//	1e23-8388608
+	//	1e23+8388608
+	// The former has an even mantissa, so "1e23" rounds to 1e23-8388608.
+	// If "1e23+8388608" is implemented as "1e23" + "8388608",
+	// that ends up computing 1e23-8388608 + 8388608 = 1e23,
+	// which rounds back to 1e23-8388608.
+	// The correct answer, of course, would be "1e23+8388608" = 1e23+8388608.
+	// This is not going to be correct until 6g has multiprecision floating point.
+	// A simpler case is "1e23+1", which should also round to 1e23+8388608.
+	Test{1e23 + 8.388608e6, "1e23+8.388608e6", "1.0000000000000001e+23"},
+	Test{1e23 + 1, "1e23+1", "1.0000000000000001e+23"},
+}
+
+func main() {
+	ok := true
+	for i := 0; i < len(tests); i++ {
+		t := tests[i]
+		v := strconv.FormatFloat(t.f, 'g', -1, 64)
+		if v != t.out {
+			println("Bad float64 const:", t.in, "want", t.out, "got", v)
+			x, err := strconv.ParseFloat(t.out, 64)
+			if err != nil {
+				println("bug120: strconv.Atof64", t.out)
+				panic("fail")
+			}
+			println("\twant exact:", strconv.FormatFloat(x, 'g', 1000, 64))
+			println("\tgot exact: ", strconv.FormatFloat(t.f, 'g', 1000, 64))
+			ok = false
+		}
+	}
+	if !ok {
+		os.Exit(1)
+	}
+}