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// run
// Check conversion of constant to float32/float64 near min/max boundaries.
// Copyright 2014 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 (
"fmt"
)
const (
m32bits = 23 // number of float32 mantissa bits
e32max = 127 // max. float32 exponent
maxExp32 = e32max - m32bits
maxMant32 = 1<<(m32bits+1) - 1
maxFloat32_0 = (maxMant32 - 0) << maxExp32
maxFloat32_1 = (maxMant32 - 1) << maxExp32
maxFloat32_2 = (maxMant32 - 2) << maxExp32
)
func init() {
if maxExp32 != 104 {
panic("incorrect maxExp32")
}
if maxMant32 != 16777215 {
panic("incorrect maxMant32")
}
if maxFloat32_0 != 340282346638528859811704183484516925440 {
panic("incorrect maxFloat32_0")
}
}
const (
m64bits = 52 // number of float64 mantissa bits
e64max = 1023 // max. float64 exponent
maxExp64 = e64max - m64bits
maxMant64 = 1<<(m64bits+1) - 1
// These expressions are not permitted due to implementation restrictions.
// maxFloat64_0 = (maxMant64-0) << maxExp64
// maxFloat64_1 = (maxMant64-1) << maxExp64
// maxFloat64_2 = (maxMant64-2) << maxExp64
// These equivalent values were computed using math/big.
maxFloat64_0 = 1.7976931348623157e308
maxFloat64_1 = 1.7976931348623155e308
maxFloat64_2 = 1.7976931348623153e308
)
func init() {
if maxExp64 != 971 {
panic("incorrect maxExp64")
}
if maxMant64 != 9007199254740991 {
panic("incorrect maxMant64")
}
}
var cvt = []struct {
val interface{}
binary string
}{
{float32(maxFloat32_0), fmt.Sprintf("%dp+%d", int32(maxMant32-0), maxExp32)},
{float32(maxFloat32_1), fmt.Sprintf("%dp+%d", int32(maxMant32-1), maxExp32)},
{float32(maxFloat32_2), fmt.Sprintf("%dp+%d", int32(maxMant32-2), maxExp32)},
{float64(maxFloat64_0), fmt.Sprintf("%dp+%d", int64(maxMant64-0), maxExp64)},
{float64(maxFloat64_1), fmt.Sprintf("%dp+%d", int64(maxMant64-1), maxExp64)},
{float64(maxFloat64_2), fmt.Sprintf("%dp+%d", int64(maxMant64-2), maxExp64)},
{float32(-maxFloat32_0), fmt.Sprintf("-%dp+%d", int32(maxMant32-0), maxExp32)},
{float32(-maxFloat32_1), fmt.Sprintf("-%dp+%d", int32(maxMant32-1), maxExp32)},
{float32(-maxFloat32_2), fmt.Sprintf("-%dp+%d", int32(maxMant32-2), maxExp32)},
{float64(-maxFloat64_0), fmt.Sprintf("-%dp+%d", int64(maxMant64-0), maxExp64)},
{float64(-maxFloat64_1), fmt.Sprintf("-%dp+%d", int64(maxMant64-1), maxExp64)},
{float64(-maxFloat64_2), fmt.Sprintf("-%dp+%d", int64(maxMant64-2), maxExp64)},
}
func main() {
bug := false
for i, c := range cvt {
s := fmt.Sprintf("%b", c.val)
if s != c.binary {
if !bug {
bug = true
fmt.Println("BUG")
}
fmt.Printf("#%d: have %s, want %s\n", i, s, c.binary)
}
}
}
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