66 lines
1.2 KiB
Go
66 lines
1.2 KiB
Go
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package pmath
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const (
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bitsize = 32 << (^uint(0) >> 63)
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maxint = int(1<<(bitsize-1) - 1)
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maxintHeadBit = 1 << (bitsize - 2)
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)
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// LogarithmicRange iterates from ceiled to power of two min to max,
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// calling cb on each iteration.
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func LogarithmicRange(min, max int, cb func(int)) {
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if min == 0 {
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min = 1
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}
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for n := CeilToPowerOfTwo(min); n <= max; n <<= 1 {
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cb(n)
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}
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}
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// IsPowerOfTwo reports whether given integer is a power of two.
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func IsPowerOfTwo(n int) bool {
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return n&(n-1) == 0
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}
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// Identity is identity.
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func Identity(n int) int {
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return n
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}
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// CeilToPowerOfTwo returns the least power of two integer value greater than
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// or equal to n.
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func CeilToPowerOfTwo(n int) int {
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if n&maxintHeadBit != 0 && n > maxintHeadBit {
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panic("argument is too large")
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}
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if n <= 2 {
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return n
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}
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n--
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n = fillBits(n)
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n++
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return n
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}
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// FloorToPowerOfTwo returns the greatest power of two integer value less than
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// or equal to n.
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func FloorToPowerOfTwo(n int) int {
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if n <= 2 {
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return n
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}
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n = fillBits(n)
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n >>= 1
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n++
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return n
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}
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func fillBits(n int) int {
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n |= n >> 1
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n |= n >> 2
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n |= n >> 4
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n |= n >> 8
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n |= n >> 16
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n |= n >> 32
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return n
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}
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