如何为无符号整数类型指定可表示的最大值?

我想知道如何在下面的循环中初始化min,迭代计算一些结构的min和max长度。

var minLen uint = ???
var maxLen uint = 0
for _, thing := range sliceOfThings {
  if minLen > thing.n { minLen = thing.n }
  if maxLen < thing.n { maxLen = thing.n }
}
if minLen > maxLen {
  // If there are no values, clamp min at 0 so that min <= max.
  minLen = 0
}

使第一次通过比较,minLen >= n。


当前回答

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
MaxUint8  = 1<<8 - 1
MaxUint16 = 1<<16 - 1
MaxUint32 = 1<<32 - 1
MaxUint64 = 1<<64 - 1

其他回答

来自数学库:https://github.com/golang/go/blob/master/src/math/const.go#L39

package main

import (
    "fmt"
    "math"
)

func main() {
    fmt.Printf("max int64: %d\n", math.MaxInt64)
}
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
MaxUint8  = 1<<8 - 1
MaxUint16 = 1<<16 - 1
MaxUint32 = 1<<32 - 1
MaxUint64 = 1<<64 - 1

使用数学包中定义的常量:

const (
    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
    MaxUint8  = 1<<8 - 1
    MaxUint16 = 1<<16 - 1
    MaxUint32 = 1<<32 - 1
    MaxUint64 = 1<<64 - 1
)

一个轻量级包包含了它们(以及其他int类型的限制和一些广泛使用的整数函数):

import (
    "fmt"
    "<Full URL>/go-imath/ix"
    "<Full URL>/go-imath/ux"
)
...
fmt.Println(ix.Minimal) // Output: -2147483648 (32-bit) or -9223372036854775808 (64-bit)
fmt.Println(ix.Maximal) // Output: 2147483647 or 9223372036854775807
fmt.Println(ux.Minimal) // Output: 0
fmt.Println(ux.Maximal) // Output: 4294967295 or 18446744073709551615

我最初使用的代码取自@nmichaels在他的回答中使用的讨论线程。现在我用了一个稍微不同的计算方法。我附上了一些评论,以防其他人有和@Arijoon一样的问题

const (
    MinUint uint = 0                 // binary: all zeroes

    // Perform a bitwise NOT to change every bit from 0 to 1
    MaxUint      = ^MinUint          // binary: all ones

    // Shift the binary number to the right (i.e. divide by two)
    // to change the high bit to 0
    MaxInt       = int(MaxUint >> 1) // binary: all ones except high bit

    // Perform another bitwise NOT to change the high bit to 1 and
    // all other bits to 0
    MinInt       = ^MaxInt           // binary: all zeroes except high bit
)

最后两个步骤是有效的,因为正数和负数在2的补数算术中是如何表示的。关于数字类型的Go语言规范部分建议读者参考维基百科的相关文章。我还没有读过,但我确实从Charles Petzold的Code一书中了解了two的补码,这是一本非常容易理解的计算机和编码基础介绍。

我将上面的代码(减去大部分注释)放入一个小整数数学包中。