Go中的“魔数”

留言

src/math/bits.go:

const SmallestNormal = 2.2250738585072014e-308 // 2**-1022

Numeric limitations


src/math/cbrt.go

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const (
		B1             = 715094163                   // (682-0.03306235651)*2**20
		B2             = 696219795                   // (664-0.03306235651)*2**20
		C              = 5.42857142857142815906e-01  // 19/35     = 0x3FE15F15F15F15F1
		D              = -7.05306122448979611050e-01 // -864/1225 = 0xBFE691DE2532C834
		E              = 1.41428571428571436819e+00  // 99/70     = 0x3FF6A0EA0EA0EA0F
		F              = 1.60714285714285720630e+00  // 45/28     = 0x3FF9B6DB6DB6DB6E
		G              = 3.57142857142857150787e-01  // 5/14      = 0x3FD6DB6DB6DB6DB7
		SmallestNormal = 2.22507385850720138309e-308 // 2**-1022  = 0x0010000000000000
	)


本地队列中的g被执行61次后，全局队列中的g得到一次被执行的机会


为什么是61？


最早是C写的，后来改成Go

https://codereview.appspot.com/10042044
最原始的提交就是61
检视中还讨论到了59[旺柴]

Issue 10042044: code review 10042044: runtime: improve scheduler fairness (Closed)

tech-talk之magicNumber-61


16294579238595022365

https://tieba.baidu.com/p/7592696329

https://www.google.com/search?q=16294579238595022365&oq=16294579238595022365&aqs=chrome..69i57j69i60.196j0j4&sourceid=chrome&ie=UTF-8


时间模块


1885年和「回到未来3」&希尔山谷，1977-5-25和「星球大战」…

还有更出名的2006-01-02 15:04:05，Go团队对时间模块“魔数”的引入，各种天马行空和意想不到的彩蛋。用吴站长话说，“颇具浪漫主义气息啊”

有意思！Go 源代码中的那些秘密：为什么 time.minWall 是 1885？

time/time.go

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const (
	// The unsigned zero year for internal calculations.
	// Must be 1 mod 400, and times before it will not compute correctly,
	// but otherwise can be changed at will.
	absoluteZeroYear = -292277022399

	// The year of the zero Time.
	// Assumed by the unixToInternal computation below.
	internalYear = 1

	// Offsets to convert between internal and absolute or Unix times.
	absoluteToInternal int64 = (absoluteZeroYear - internalYear) * 365.2425 * secondsPerDay
	internalToAbsolute       = -absoluteToInternal

	unixToInternal int64 = (1969*365 + 1969/4 - 1969/100 + 1969/400) * secondsPerDay
	internalToUnix int64 = -unixToInternal

	wallToInternal int64 = (1884*365 + 1884/4 - 1884/100 + 1884/400) * secondsPerDay
	internalToWall int64 = -wallToInternal
)