golang floatexample_test 代码
文件路径：/src/math/big/floatexample_test.go
/ 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
}