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73 lines
1.7 KiB
73 lines
1.7 KiB
// from https://github.com/xtaci/smux/blob/master/alloc.go
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package byte_alloc
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import (
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"sync"
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)
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// magic number
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var debruijinPos = [...]byte{0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31}
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// Allocator for incoming frames, optimized to prevent overwriting after zeroing
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type Allocator struct {
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buffers []sync.Pool
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}
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// NewAllocator initiates a []byte allocator for frames less than 1048576 bytes,
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// the waste(memory fragmentation) of space allocation is guaranteed to be
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// no more than 50%.
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func NewAllocator() *Allocator {
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alloc := new(Allocator)
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alloc.buffers = make([]sync.Pool, 21) // 1B -> 1M
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for k := range alloc.buffers {
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size := 1 << uint32(k)
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alloc.buffers[k].New = func() interface{} {
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return make([]byte, size)
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}
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}
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return alloc
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}
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// Get a []byte from pool with most appropriate cap
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func (alloc *Allocator) Get(size int) []byte {
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if size <= 0 {
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return nil
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}
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if size > 1048576 {
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return make([]byte, size)
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}
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bits := msb(size)
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if size == 1<<bits {
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return alloc.buffers[bits].Get().([]byte)[:size]
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} else {
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return alloc.buffers[bits+1].Get().([]byte)[:size]
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}
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}
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// Put returns a []byte to pool for future use,
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// which the cap must be exactly 2^n
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func (alloc *Allocator) Put(buf []byte) {
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bufCap := cap(buf)
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bits := msb(bufCap)
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if bufCap == 0 || bufCap > 65536 || bufCap != 1<<bits {
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return
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}
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alloc.buffers[bits].Put(buf)
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return
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}
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// msb return the pos of most significiant bit
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// Equivalent to: uint(math.Floor(math.Log2(float64(n))))
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// http://supertech.csail.mit.edu/papers/debruijn.pdf
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func msb(size int) byte {
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v := uint32(size)
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v |= v >> 1
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v |= v >> 2
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v |= v >> 4
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v |= v >> 8
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v |= v >> 16
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return debruijinPos[(v*0x07C4ACDD)>>27]
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}
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