github.com/riscv/riscv-go@v0.0.0-20200123204226-124ebd6fcc8e/src/math/big/floatexample_test.go (about)

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package big_test
     6  
     7  import (
     8  	"fmt"
     9  	"math"
    10  	"math/big"
    11  )
    12  
    13  func ExampleFloat_Add() {
    14  	// Operate on numbers of different precision.
    15  	var x, y, z big.Float
    16  	x.SetInt64(1000)          // x is automatically set to 64bit precision
    17  	y.SetFloat64(2.718281828) // y is automatically set to 53bit precision
    18  	z.SetPrec(32)
    19  	z.Add(&x, &y)
    20  	fmt.Printf("x = %.10g (%s, prec = %d, acc = %s)\n", &x, x.Text('p', 0), x.Prec(), x.Acc())
    21  	fmt.Printf("y = %.10g (%s, prec = %d, acc = %s)\n", &y, y.Text('p', 0), y.Prec(), y.Acc())
    22  	fmt.Printf("z = %.10g (%s, prec = %d, acc = %s)\n", &z, z.Text('p', 0), z.Prec(), z.Acc())
    23  	// Output:
    24  	// x = 1000 (0x.fap+10, prec = 64, acc = Exact)
    25  	// y = 2.718281828 (0x.adf85458248cd8p+2, prec = 53, acc = Exact)
    26  	// z = 1002.718282 (0x.faadf854p+10, prec = 32, acc = Below)
    27  }
    28  
    29  func ExampleFloat_shift() {
    30  	// Implement Float "shift" by modifying the (binary) exponents directly.
    31  	for s := -5; s <= 5; s++ {
    32  		x := big.NewFloat(0.5)
    33  		x.SetMantExp(x, x.MantExp(nil)+s) // shift x by s
    34  		fmt.Println(x)
    35  	}
    36  	// Output:
    37  	// 0.015625
    38  	// 0.03125
    39  	// 0.0625
    40  	// 0.125
    41  	// 0.25
    42  	// 0.5
    43  	// 1
    44  	// 2
    45  	// 4
    46  	// 8
    47  	// 16
    48  }
    49  
    50  func ExampleFloat_Cmp() {
    51  	inf := math.Inf(1)
    52  	zero := 0.0
    53  
    54  	operands := []float64{-inf, -1.2, -zero, 0, +1.2, +inf}
    55  
    56  	fmt.Println("   x     y  cmp")
    57  	fmt.Println("---------------")
    58  	for _, x64 := range operands {
    59  		x := big.NewFloat(x64)
    60  		for _, y64 := range operands {
    61  			y := big.NewFloat(y64)
    62  			fmt.Printf("%4g  %4g  %3d\n", x, y, x.Cmp(y))
    63  		}
    64  		fmt.Println()
    65  	}
    66  
    67  	// Output:
    68  	//    x     y  cmp
    69  	// ---------------
    70  	// -Inf  -Inf    0
    71  	// -Inf  -1.2   -1
    72  	// -Inf    -0   -1
    73  	// -Inf     0   -1
    74  	// -Inf   1.2   -1
    75  	// -Inf  +Inf   -1
    76  	//
    77  	// -1.2  -Inf    1
    78  	// -1.2  -1.2    0
    79  	// -1.2    -0   -1
    80  	// -1.2     0   -1
    81  	// -1.2   1.2   -1
    82  	// -1.2  +Inf   -1
    83  	//
    84  	//   -0  -Inf    1
    85  	//   -0  -1.2    1
    86  	//   -0    -0    0
    87  	//   -0     0    0
    88  	//   -0   1.2   -1
    89  	//   -0  +Inf   -1
    90  	//
    91  	//    0  -Inf    1
    92  	//    0  -1.2    1
    93  	//    0    -0    0
    94  	//    0     0    0
    95  	//    0   1.2   -1
    96  	//    0  +Inf   -1
    97  	//
    98  	//  1.2  -Inf    1
    99  	//  1.2  -1.2    1
   100  	//  1.2    -0    1
   101  	//  1.2     0    1
   102  	//  1.2   1.2    0
   103  	//  1.2  +Inf   -1
   104  	//
   105  	// +Inf  -Inf    1
   106  	// +Inf  -1.2    1
   107  	// +Inf    -0    1
   108  	// +Inf     0    1
   109  	// +Inf   1.2    1
   110  	// +Inf  +Inf    0
   111  }
   112  
   113  func ExampleRoundingMode() {
   114  	operands := []float64{2.6, 2.5, 2.1, -2.1, -2.5, -2.6}
   115  
   116  	fmt.Print("   x")
   117  	for mode := big.ToNearestEven; mode <= big.ToPositiveInf; mode++ {
   118  		fmt.Printf("  %s", mode)
   119  	}
   120  	fmt.Println()
   121  
   122  	for _, f64 := range operands {
   123  		fmt.Printf("%4g", f64)
   124  		for mode := big.ToNearestEven; mode <= big.ToPositiveInf; mode++ {
   125  			// sample operands above require 2 bits to represent mantissa
   126  			// set binary precision to 2 to round them to integer values
   127  			f := new(big.Float).SetPrec(2).SetMode(mode).SetFloat64(f64)
   128  			fmt.Printf("  %*g", len(mode.String()), f)
   129  		}
   130  		fmt.Println()
   131  	}
   132  
   133  	// Output:
   134  	//    x  ToNearestEven  ToNearestAway  ToZero  AwayFromZero  ToNegativeInf  ToPositiveInf
   135  	//  2.6              3              3       2             3              2              3
   136  	//  2.5              2              3       2             3              2              3
   137  	//  2.1              2              2       2             3              2              3
   138  	// -2.1             -2             -2      -2            -3             -3             -2
   139  	// -2.5             -2             -3      -2            -3             -3             -2
   140  	// -2.6             -3             -3      -2            -3             -3             -2
   141  }