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https://github.com/golang/go
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59 lines
1.8 KiB
Go
59 lines
1.8 KiB
Go
// $G $D/$F.go && $L $F.$A && ./$A.out || echo BUG: bug120
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import "strconv";
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type Test struct {
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f float64;
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in string;
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out string;
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}
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var tests = []Test (
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Test( 123.5, "123.5", "123.5" ),
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Test( 456.7, "456.7", "456.7" ),
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Test( 1e23+8.5e6, "1e23+8.5e6", "1.0000000000000001e+23" ),
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Test( 100000000000000008388608, "100000000000000008388608", "1.0000000000000001e+23" ),
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Test( 1e23+8388609, "1e23+8388609", "1.0000000000000001e+23" ),
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// "x" = the floating point value from converting the string x.
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// These are exactly representable in 64-bit floating point:
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// 1e23-8388608
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// 1e23+8388608
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// The former has an even mantissa, so "1e23" rounds to 1e23-8388608.
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// If "1e23+8388608" is implemented as "1e23" + "8388608",
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// that ends up computing 1e23-8388608 + 8388608 = 1e23,
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// which rounds back to 1e23-8388608.
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// The correct answer, of course, would be "1e23+8388608" = 1e23+8388608.
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// This is not going to be correct until 6g has multiprecision floating point.
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// A simpler case is "1e23+1", which should also round to 1e23+8388608.
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Test( 1e23+8.388608e6, "1e23+8.388608e6", "1.0000000000000001e+23" ),
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Test( 1e23+1, "1e23+1", "1.0000000000000001e+23" ),
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)
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func main() {
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ok := true;
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for i := 0; i < len(tests); i++ {
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t := tests[i];
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v := strconv.Ftoa64(t.f, 'g', -1);
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if v != t.out {
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println("Bad float64 const:", t.in, "want", t.out, "got", v);
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x, err := strconv.Atof64(t.out);
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if err != nil {
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panicln("bug120: strconv.Atof64", t.out);
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}
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println("\twant exact:", strconv.Ftoa64(x, 'g', 1000));
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println("\tgot exact: ", strconv.Ftoa64(t.f, 'g', 1000));
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ok = false;
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}
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}
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if !ok {
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sys.Exit(1);
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}
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}
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