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Source file test/fixedbugs/bug120.go

Documentation: test/fixedbugs

  // 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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