go——map源码之元素数量和桶数量

go语言中，map的桶的数量是根据元素数量经过计算得出的，计算方法如下：

package main

import (
	"fmt"
)

func main() {

	res := calcB(1000)
	fmt.Println("元素数量:1000,B:", res, "桶数量", calcBucket(res))

}

func calcBucket(B uint8) int {
	res := 1 << B
	return res
}

func calcB(count int) uint8 {
	var B uint8 = 0
	for overFactor(count, B) {
		B++
	}
	return B
}

func overFactor(count int, B uint8) bool {
	const loadFactorNum = 13
	const loadFactorDen = 2
	const bucketCnt = 8
	return count > bucketCnt && uintptr(count) > loadFactorNum*(bucketShift(B)/loadFactorDen)
}

func bucketShift(b uint8) uintptr {
	return uintptr(1) << (b & ((4<<(^uintptr(0)>>63))*8 - 1))
}