精确计算

decimal

package main

import (
    "fmt"
    "github.com/prometheus/common/log"
    "github.com/shopspring/decimal"
)

// imprecise 不精确demo
func imprecise() {
    a := 2.07
    b := 1.0
    c := a - b
    fmt.Printf("c=%v\n", c)
    //c=1.0699999999999998
}

func main() {
    a := "2.07"
    b := "1.0"
    ad, err := decimal.NewFromString(a)
    if err != nil {
        log.Error(err)
    }
    bd, err := decimal.NewFromString(b)
    if err != nil {
        log.Error(err)
    }
    cd := ad.Sub(bd)
    c, _ := cd.Float64()
    fmt.Printf("c=%v\n", c)
}

官方包

// Pct x,y百分比值
func Pct(x, y float64) float64 {
    xb := big.NewFloat(x)
    yb := big.NewFloat(y)
    pct := big.NewFloat(100)

    res, _ := xb.Mul(xb.Quo(xb, yb), pct).Float64()
    res = math.Trunc(res*1e2) * 1e-2
    return res
}

func main() {
    // 有理数
    price := big.NewRat(48, 1) // 48/1
    total := big.NewRat(95, 1) // 95/1
    pct := big.NewRat(100, 1)  // 100/1

    // 注：Rat结构体对应方法，只针对结果，故无论是price.Mul或者total.Mul效果是一样的
    tf, _ := total.Mul(total.Quo(price, total), pct).Float64() // 该表达式等价于-->价格/总价*100
    t := math.Trunc(tf*1e2) * 1e-2                             // 浮点类型保留小数点2位
    fmt.Println(t)

    fmt.Println(Pct(3,78))
}