1// run
2
3// Copyright 2009 The Go Authors. All rights reserved.
4// Use of this source code is governed by a BSD-style
5// license that can be found in the LICENSE file.
6
7package main
8
9import "os"
10import "strconv"
11
12type Test struct {
13	f   float64
14	in  string
15	out string
16}
17
18var tests = []Test{
19	Test{123.5, "123.5", "123.5"},
20	Test{456.7, "456.7", "456.7"},
21	Test{1e23 + 8.5e6, "1e23+8.5e6", "1.0000000000000001e+23"},
22	Test{100000000000000008388608, "100000000000000008388608", "1.0000000000000001e+23"},
23	Test{1e23 + 8388609, "1e23+8388609", "1.0000000000000001e+23"},
24
25	// "x" = the floating point value from converting the string x.
26	// These are exactly representable in 64-bit floating point:
27	//	1e23-8388608
28	//	1e23+8388608
29	// The former has an even mantissa, so "1e23" rounds to 1e23-8388608.
30	// If "1e23+8388608" is implemented as "1e23" + "8388608",
31	// that ends up computing 1e23-8388608 + 8388608 = 1e23,
32	// which rounds back to 1e23-8388608.
33	// The correct answer, of course, would be "1e23+8388608" = 1e23+8388608.
34	// This is not going to be correct until 6g has multiprecision floating point.
35	// A simpler case is "1e23+1", which should also round to 1e23+8388608.
36	Test{1e23 + 8.388608e6, "1e23+8.388608e6", "1.0000000000000001e+23"},
37	Test{1e23 + 1, "1e23+1", "1.0000000000000001e+23"},
38}
39
40func main() {
41	ok := true
42	for i := 0; i < len(tests); i++ {
43		t := tests[i]
44		v := strconv.FormatFloat(t.f, 'g', -1, 64)
45		if v != t.out {
46			println("Bad float64 const:", t.in, "want", t.out, "got", v)
47			x, err := strconv.ParseFloat(t.out, 64)
48			if err != nil {
49				println("bug120: strconv.Atof64", t.out)
50				panic("fail")
51			}
52			println("\twant exact:", strconv.FormatFloat(x, 'g', 1000, 64))
53			println("\tgot exact: ", strconv.FormatFloat(t.f, 'g', 1000, 64))
54			ok = false
55		}
56	}
57	if !ok {
58		os.Exit(1)
59	}
60}
61