alloc.go

package gmux

import (
	"errors"
	"sync"
)

var (
	defaultAllocator *Allocator
	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}
)

func init() {
	defaultAllocator = NewAllocator()
}
type Allocator struct {
	buffers []sync.Pool
}

func NewAllocator() *Allocator {
	alloc := new(Allocator)
	alloc.buffers = make([]sync.Pool, 17)
	for k := range alloc.buffers {
		i := k
		alloc.buffers[k].New = func() interface{} {
			return make([]byte, 1 << uint32(i))
		}
	}
	return alloc
}

func (alloc *Allocator) Get(size int) []byte {
	if size <= 0 || size > 65536 {
		return nil
	}

	bits := msb(size)
	if size == 1<<bits {
		return alloc.buffers[bits].Get().([]byte)[:size]
	} else {
		return alloc.buffers[bits+1].Get().([]byte)[:size]
	}
}

func (alloc *Allocator) Put(buf []byte) error {
	bits := msb(cap(buf))
	if cap(buf) == 0 || cap(buf) > 65536 || cap(buf) != 1<<bits {
		return errors.New("allocator Put() incorrect buffer size")
	}

	alloc.buffers[bits].Put(buf)
	return nil
}

func msb(size int) byte {
	v := uint32(size)
	v |= v >> 1
	v |= v >> 2
	v |= v >> 4
	v |= v >> 8
	v |= v >> 16
	return debruijinPos[(v*0x07C4ACDD)>>27]
}