【Golang】 Go语言中数值类型的默认常量值

Golang中默认数值类型的常量值（PI,）

在编程中，数学是非常关键的方面，我们需要非常定期地执行某些数学运算，因此 golang 的标准库有一个包来提供一些非常常用的数学函数和过程，有些开发人员自己定义一套默认配置常量，如： MAX_INT，MIN_INT，MAX_FLOAT 等等；其实大可不用这么定义，在Golang的数学包 math 中已经为开发人员预先定义过了，使用起来非常方便 就在math

数学常量

有一些常量，如已经在 golang 标准库的数学包中定义为常量。它们的精度直到 float64 值中存储的 15 位数字

测试代码

package main

import (
    "fmt"
    "math"
)

func main() {
    fmt.Println("Pi = ", math.Pi)
    fmt.Println("E = ", math.E)
    fmt.Println("Phi = ", math.Phi)
    fmt.Println("Sqrt of 2 = ", math.Sqrt2)
    fmt.Println("Naturla Log 2 = ", math.Ln2)
    fmt.Println("Naturla Log 10 = ", math.Ln10)
    fmt.Println(math.MaxInt)
	fmt.Println(math.MaxInt8)
	fmt.Println(math.MaxUint8)
	fmt.Println(math.MaxInt)
	fmt.Println(math.MaxUint)
}

测试代码结果

$ go run basic-functions/constants.go
Pi =  3.141592653589793
E =  2.718281828459045
Phi =  1.618033988749895
Sqrt of 2 =  1.4142135623730951
Naturla Log 2 =  0.6931471805599453
Naturla Log 10 =  2.302585092994046
MaxInt =  9223372036854775807
MaxInt8 =  127
MaxUint8 =  255
MaxInt =  9223372036854775807

源码

源码位置：$GOPATH/src/math/const.go

// Copyright 2009 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 math provides basic constants and mathematical functions.
//
// This package does not guarantee bit-identical results across architectures.
package math

// Mathematical constants.
const (
	E   = 2.71828182845904523536028747135266249775724709369995957496696763 // https://oeis.org/A001113
	Pi  = 3.14159265358979323846264338327950288419716939937510582097494459 // https://oeis.org/A000796
	Phi = 1.61803398874989484820458683436563811772030917980576286213544862 // https://oeis.org/A001622

	Sqrt2   = 1.41421356237309504880168872420969807856967187537694807317667974 // https://oeis.org/A002193
	SqrtE   = 1.64872127070012814684865078781416357165377610071014801157507931 // https://oeis.org/A019774
	SqrtPi  = 1.77245385090551602729816748334114518279754945612238712821380779 // https://oeis.org/A002161
	SqrtPhi = 1.27201964951406896425242246173749149171560804184009624861664038 // https://oeis.org/A139339

	Ln2    = 0.693147180559945309417232121458176568075500134360255254120680009 // https://oeis.org/A002162
	Log2E  = 1 / Ln2
	Ln10   = 2.30258509299404568401799145468436420760110148862877297603332790 // https://oeis.org/A002392
	Log10E = 1 / Ln10
)

// Floating-point limit values.
// Max is the largest finite value representable by the type.
// SmallestNonzero is the smallest positive, non-zero value representable by the type.
const (
	MaxFloat32             = 0x1p127 * (1 + (1 - 0x1p-23)) // 3.40282346638528859811704183484516925440e+38
	SmallestNonzeroFloat32 = 0x1p-126 * 0x1p-23            // 1.401298464324817070923729583289916131280e-45

	MaxFloat64             = 0x1p1023 * (1 + (1 - 0x1p-52)) // 1.79769313486231570814527423731704356798070e+308
	SmallestNonzeroFloat64 = 0x1p-1022 * 0x1p-52            // 4.9406564584124654417656879286822137236505980e-324
)

// Integer limit values.
const (
	intSize = 32 << (^uint(0) >> 63) // 32 or 64

	MaxInt    = 1<<(intSize-1) - 1
	MinInt    = -1 << (intSize - 1)
	MaxInt8   = 1<<7 - 1
	MinInt8   = -1 << 7
	MaxInt16  = 1<<15 - 1
	MinInt16  = -1 << 15
	MaxInt32  = 1<<31 - 1
	MinInt32  = -1 << 31
	MaxInt64  = 1<<63 - 1
	MinInt64  = -1 << 63
	MaxUint   = 1<<intSize - 1
	MaxUint8  = 1<<8 - 1
	MaxUint16 = 1<<16 - 1
	MaxUint32 = 1<<32 - 1
	MaxUint64 = 1<<64 - 1
)

参考

官方文档