mirror of
https://github.com/golang/go
synced 2024-10-02 18:18:33 -06:00
99 lines
2.7 KiB
Go
99 lines
2.7 KiB
Go
// run
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// Check conversion of constant to float32/float64 near min/max boundaries.
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// Copyright 2014 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 (
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"fmt"
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)
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const (
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m32bits = 23 // number of float32 mantissa bits
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e32max = 127 // max. float32 exponent
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maxExp32 = e32max - m32bits
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maxMant32 = 1<<(m32bits+1) - 1
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maxFloat32_0 = (maxMant32 - 0) << maxExp32
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maxFloat32_1 = (maxMant32 - 1) << maxExp32
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maxFloat32_2 = (maxMant32 - 2) << maxExp32
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)
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func init() {
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if maxExp32 != 104 {
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panic("incorrect maxExp32")
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}
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if maxMant32 != 16777215 {
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panic("incorrect maxMant32")
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}
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if maxFloat32_0 != 340282346638528859811704183484516925440 {
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panic("incorrect maxFloat32_0")
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}
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}
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const (
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m64bits = 52 // number of float64 mantissa bits
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e64max = 1023 // max. float64 exponent
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maxExp64 = e64max - m64bits
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maxMant64 = 1<<(m64bits+1) - 1
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// These expressions are not permitted due to implementation restrictions.
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// maxFloat64_0 = (maxMant64-0) << maxExp64
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// maxFloat64_1 = (maxMant64-1) << maxExp64
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// maxFloat64_2 = (maxMant64-2) << maxExp64
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// These equivalent values were computed using math/big.
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maxFloat64_0 = 1.7976931348623157e308
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maxFloat64_1 = 1.7976931348623155e308
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maxFloat64_2 = 1.7976931348623153e308
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)
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func init() {
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if maxExp64 != 971 {
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panic("incorrect maxExp64")
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}
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if maxMant64 != 9007199254740991 {
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panic("incorrect maxMant64")
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}
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}
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var cvt = []struct {
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val interface{}
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binary string
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}{
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{float32(maxFloat32_0), fmt.Sprintf("%dp+%d", int32(maxMant32-0), maxExp32)},
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{float32(maxFloat32_1), fmt.Sprintf("%dp+%d", int32(maxMant32-1), maxExp32)},
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{float32(maxFloat32_2), fmt.Sprintf("%dp+%d", int32(maxMant32-2), maxExp32)},
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{float64(maxFloat64_0), fmt.Sprintf("%dp+%d", int64(maxMant64-0), maxExp64)},
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{float64(maxFloat64_1), fmt.Sprintf("%dp+%d", int64(maxMant64-1), maxExp64)},
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{float64(maxFloat64_2), fmt.Sprintf("%dp+%d", int64(maxMant64-2), maxExp64)},
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{float32(-maxFloat32_0), fmt.Sprintf("-%dp+%d", int32(maxMant32-0), maxExp32)},
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{float32(-maxFloat32_1), fmt.Sprintf("-%dp+%d", int32(maxMant32-1), maxExp32)},
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{float32(-maxFloat32_2), fmt.Sprintf("-%dp+%d", int32(maxMant32-2), maxExp32)},
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{float64(-maxFloat64_0), fmt.Sprintf("-%dp+%d", int64(maxMant64-0), maxExp64)},
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{float64(-maxFloat64_1), fmt.Sprintf("-%dp+%d", int64(maxMant64-1), maxExp64)},
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{float64(-maxFloat64_2), fmt.Sprintf("-%dp+%d", int64(maxMant64-2), maxExp64)},
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}
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func main() {
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bug := false
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for i, c := range cvt {
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s := fmt.Sprintf("%b", c.val)
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if s != c.binary {
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if !bug {
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bug = true
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fmt.Println("BUG")
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}
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fmt.Printf("#%d: have %s, want %s\n", i, s, c.binary)
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}
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}
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}
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