issue14651.go

     1  // run
     2  
     3  // Copyright 2016 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  // This test checks if the compiler's internal constant
     8  // arithmetic correctly rounds up floating-point values
     9  // that become the smallest denormal value.
    10  //
    11  // See also related issue 14553 and test issue14553.go.
    12  
    13  package main
    14  
    15  import (
    16  	"fmt"
    17  	"math"
    18  )
    19  
    20  const (
    21  	p149 = 1.0 / (1 << 149) // 1p-149
    22  	p500 = 1.0 / (1 << 500) // 1p-500
    23  	p1074 = p500 * p500 / (1<<74) // 1p-1074
    24  )
    25  
    26  const (
    27  	m0000p149 = 0x0 / 16.0 * p149 // = 0.0000p-149
    28  	m1000p149 = 0x8 / 16.0 * p149 // = 0.1000p-149
    29  	m1001p149 = 0x9 / 16.0 * p149 // = 0.1001p-149
    30  	m1011p149 = 0xb / 16.0 * p149 // = 0.1011p-149
    31  	m1100p149 = 0xc / 16.0 * p149 // = 0.1100p-149
    32  
    33  	m0000p1074 = 0x0 / 16.0 * p1074 // = 0.0000p-1074
    34  	m1000p1074 = 0x8 / 16.0 * p1074 // = 0.1000p-1074
    35  	m1001p1074 = 0x9 / 16.0 * p1074 // = 0.1001p-1074
    36  	m1011p1074 = 0xb / 16.0 * p1074 // = 0.1011p-1074
    37  	m1100p1074 = 0xc / 16.0 * p1074 // = 0.1100p-1074
    38  )
    39  
    40  func main() {
    41  	test32(float32(m0000p149), f32(m0000p149))
    42  	test32(float32(m1000p149), f32(m1000p149))
    43  	test32(float32(m1001p149), f32(m1001p149))
    44  	test32(float32(m1011p149), f32(m1011p149))
    45  	test32(float32(m1100p149), f32(m1100p149))
    46  
    47  	test64(float64(m0000p1074), f64(m0000p1074))
    48  	test64(float64(m1000p1074), f64(m1000p1074))
    49  	test64(float64(m1001p1074), f64(m1001p1074))
    50  	test64(float64(m1011p1074), f64(m1011p1074))
    51  	test64(float64(m1100p1074), f64(m1100p1074))
    52  }
    53  
    54  func f32(x float64) float32 { return float32(x) }
    55  func f64(x float64) float64 { return float64(x) }
    56  
    57  func test32(a, b float32) {
    58  	abits := math.Float32bits(a)
    59  	bbits := math.Float32bits(b)
    60  	if abits != bbits {
    61  		panic(fmt.Sprintf("%08x != %08x\n", abits, bbits))
    62  	}
    63  }
    64  
    65  func test64(a, b float64) {
    66  	abits := math.Float64bits(a)
    67  	bbits := math.Float64bits(b)
    68  	if abits != bbits {
    69  		panic(fmt.Sprintf("%016x != %016x\n", abits, bbits))
    70  	}
    71  }
    72
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