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# Source file src/math/big/floatexample_test.go

## Documentation: math/big

```  // Copyright 2015 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 big_test

import (
"fmt"
"math"
"math/big"
)

func ExampleFloat_Add() {
// Operate on numbers of different precision.
var x, y, z big.Float
x.SetInt64(1000)          // x is automatically set to 64bit precision
y.SetFloat64(2.718281828) // y is automatically set to 53bit precision
z.SetPrec(32)
z.Add(&x, &y)
fmt.Printf("x = %.10g (%s, prec = %d, acc = %s)\n", &x, x.Text('p', 0), x.Prec(), x.Acc())
fmt.Printf("y = %.10g (%s, prec = %d, acc = %s)\n", &y, y.Text('p', 0), y.Prec(), y.Acc())
fmt.Printf("z = %.10g (%s, prec = %d, acc = %s)\n", &z, z.Text('p', 0), z.Prec(), z.Acc())
// Output:
// x = 1000 (0x.fap+10, prec = 64, acc = Exact)
// y = 2.718281828 (0x.adf85458248cd8p+2, prec = 53, acc = Exact)
// z = 1002.718282 (0x.faadf854p+10, prec = 32, acc = Below)
}

func ExampleFloat_shift() {
// Implement Float "shift" by modifying the (binary) exponents directly.
for s := -5; s <= 5; s++ {
x := big.NewFloat(0.5)
x.SetMantExp(x, x.MantExp(nil)+s) // shift x by s
fmt.Println(x)
}
// Output:
// 0.015625
// 0.03125
// 0.0625
// 0.125
// 0.25
// 0.5
// 1
// 2
// 4
// 8
// 16
}

func ExampleFloat_Cmp() {
inf := math.Inf(1)
zero := 0.0

operands := []float64{-inf, -1.2, -zero, 0, +1.2, +inf}

fmt.Println("   x     y  cmp")
fmt.Println("---------------")
for _, x64 := range operands {
x := big.NewFloat(x64)
for _, y64 := range operands {
y := big.NewFloat(y64)
fmt.Printf("%4g  %4g  %3d\n", x, y, x.Cmp(y))
}
fmt.Println()
}

// Output:
//    x     y  cmp
// ---------------
// -Inf  -Inf    0
// -Inf  -1.2   -1
// -Inf    -0   -1
// -Inf     0   -1
// -Inf   1.2   -1
// -Inf  +Inf   -1
//
// -1.2  -Inf    1
// -1.2  -1.2    0
// -1.2    -0   -1
// -1.2     0   -1
// -1.2   1.2   -1
// -1.2  +Inf   -1
//
//   -0  -Inf    1
//   -0  -1.2    1
//   -0    -0    0
//   -0     0    0
//   -0   1.2   -1
//   -0  +Inf   -1
//
//    0  -Inf    1
//    0  -1.2    1
//    0    -0    0
//    0     0    0
//    0   1.2   -1
//    0  +Inf   -1
//
//  1.2  -Inf    1
//  1.2  -1.2    1
//  1.2    -0    1
//  1.2     0    1
//  1.2   1.2    0
//  1.2  +Inf   -1
//
// +Inf  -Inf    1
// +Inf  -1.2    1
// +Inf    -0    1
// +Inf     0    1
// +Inf   1.2    1
// +Inf  +Inf    0
}

func ExampleRoundingMode() {
operands := []float64{2.6, 2.5, 2.1, -2.1, -2.5, -2.6}

fmt.Print("   x")
for mode := big.ToNearestEven; mode <= big.ToPositiveInf; mode++ {
fmt.Printf("  %s", mode)
}
fmt.Println()

for _, f64 := range operands {
fmt.Printf("%4g", f64)
for mode := big.ToNearestEven; mode <= big.ToPositiveInf; mode++ {
// sample operands above require 2 bits to represent mantissa
// set binary precision to 2 to round them to integer values
f := new(big.Float).SetPrec(2).SetMode(mode).SetFloat64(f64)
fmt.Printf("  %*g", len(mode.String()), f)
}
fmt.Println()
}

// Output:
//    x  ToNearestEven  ToNearestAway  ToZero  AwayFromZero  ToNegativeInf  ToPositiveInf
//  2.6              3              3       2             3              2              3
//  2.5              2              3       2             3              2              3
//  2.1              2              2       2             3              2              3
// -2.1             -2             -2      -2            -3             -3             -2
// -2.5             -2             -3      -2            -3             -3             -2
// -2.6             -3             -3      -2            -3             -3             -2
}

```

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