Golang使用Decimal库避免运算中精度损失详细步骤

a := 1136.1
b := a * 100
fmt.Println(b) // 正确结果应该是 113610 但输出 113609.99999999999

c := 1.7
fmt.Println(a - c) // 正确结果应该是 1134.4 但输出 1134.3999999999999
fmt.Println(b - c) // 正确结果应该是 113608.3 但输出 113608.29999999999

go get github.com/shopspring/decimal

import "github.com/shopspring/decimal"

package main

import (
	"fmt"
	"github.com/shopspring/decimal"
)

func main() {
	a := decimal.NewFromFloat(1136.1)
	b := a.Mul(decimal.NewFromInt(100))
	fmt.Println(b) // 正确输出 113610

	c := decimal.NewFromFloat(1.7)
	fmt.Println(a.Sub(c)) // 正确输出 1134.4
	fmt.Println(b.Sub(c)) // 正确输出 113608.3
}

package main

import (
	"fmt"
	"github.com/shopspring/decimal"
)

func main() {
	a := decimal.NewFromFloat(1.52)
	b := decimal.NewFromFloat(0.02)

	// 加减乘除运算
	c := a.Add(b) // 1.52 + 0.02 = 1.54
	d := a.Sub(b) // 1.52 - 0.02 = 1.5
	e := a.Mul(b) // 1.52 * 0.02 = 0.0304
	f := a.Div(b) // 1.52 / 0.02 = 76
	fmt.Println(a, b, c, d, e, f)

	// 对于保留小数的处理
	pi := decimal.NewFromFloat(3.1415926535897932384626)
	pi1 := pi.Round(3)    // 对pi值四舍五入保留3位小数
	fmt.Println(pi1)       // 3.142
	pi2 := pi.Truncate(3) // 对pi值保留3位小数之后直接舍弃
	fmt.Println(pi2)       // 3.141
}

var a float64
var b = "69.77"
var c int64

d, err := decimal.NewFromString(b)
if err != nil {
	fmt.Println(err.Error())
}

a, _ = d.Float64()
fmt.Println(a) // float64 69.77

c = d.IntPart() // 舍去小数取整
fmt.Println(c)  // int64 69

b = decimal.NewFromInt(c).String()
fmt.Println(b) // string 69

c = d.Round(0).IntPart() // 不保留小数四舍五入取整
fmt.Println(c)           // int64 70

n1 := decimal.NewFromFloat(-1.23)
n2 := decimal.NewFromInt(3)
n3, _ := decimal.NewFromString("0")

n1.Abs()                  // 取绝对值
n1.Equal(n2)              // n1 是否与 n2 相等
n1.LessThan(n2)           // n1 是否小于 n2
n1.LessThanOrEqual(n2)    // n1 是否小于或等于 n2
n1.GreaterThan(n2)        // n1 是否大于 n2
n1.GreaterThanOrEqual(n2) // n1 是否大于或等于 n2
n3.IsZero()               // n3 是否为0

package main

import (
	"fmt"
	"github.com/shopspring/decimal"
	"reflect"
)

func main() {
	n1 := decimal.NewFromFloat(3.14)
	var n2 string
	var n3 float64
	var n4 int64
	var n5 decimal.Decimal

	n2 = n1.String()
	n3, _ = n1.Float64()
	n4 = n1.IntPart()

	fmt.Printf("n1 = %v, type = %v\n", n1, reflect.TypeOf(n1).String())
	// n1 = 3.14, type = decimal.Decimal
	fmt.Printf("n2 = %v, type = %v\n", n2, reflect.TypeOf(n2).String())
	// n2 = 3.14, type = string
	fmt.Printf("n3 = %v, type = %v\n", n3, reflect.TypeOf(n3).String())
	// n3 = 3.14, type = float64
	fmt.Printf("n4 = %v, type = %v\n", n4, reflect.TypeOf(n4).String())
	// n4 = 3, type = int64
	fmt.Printf("n5 = %v, type = %v\n", n5, reflect.TypeOf(n5).String())
	// n5 = 0, type = decimal.Decimal
}