go bug120 源码
golang bug120 代码
文件路径：/test/fixedbugs/bug120.go
// 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)
}
}
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