mirror of
https://github.com/golang/go
synced 2024-11-22 07:34:40 -07:00
60 lines
1.8 KiB
Go
60 lines
1.8 KiB
Go
// $G $D/$F.go && $L $F.$A && ./$A.out || echo BUG: bug120
|
|
|
|
// 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.Ftoa64(t.f, 'g', -1);
|
|
if v != t.out {
|
|
println("Bad float64 const:", t.in, "want", t.out, "got", v);
|
|
x, err := strconv.Atof64(t.out);
|
|
if err != nil {
|
|
panicln("bug120: strconv.Atof64", t.out);
|
|
}
|
|
println("\twant exact:", strconv.Ftoa64(x, 'g', 1000));
|
|
println("\tgot exact: ", strconv.Ftoa64(t.f, 'g', 1000));
|
|
ok = false;
|
|
}
|
|
}
|
|
if !ok {
|
|
os.Exit(1);
|
|
}
|
|
}
|