package pool

import (
	"math/bits"
	"sync"
)

const (
	// number of pools.
	// pool sizes: [1<<0 ~ 1<<(num-1)] bytes, [1B~64KB].
	num     = 17
	maxsize = 1 << (num - 1)
)

var (
	sizes [num]int
	pools [num]sync.Pool
)

func init() {
	for i := 0; i < num; i++ {
		size := 1 << i
		sizes[i] = size
		pools[i].New = func() interface{} {
			return make([]byte, size)
		}
	}
}

// GetBuffer gets a buffer from pool, size should in range: [1, 65536],
// otherwise, this function will call make([]byte, size) directly.
func GetBuffer(size int) []byte {
	if size >= 1 && size <= maxsize {
		i := bits.Len32(uint32(size)) - 1
		if sizes[i] < size {
			i += 1
		}
		return pools[i].Get().([]byte)[:size]
	}
	return make([]byte, size)
}

// PutBuffer puts a buffer into pool.
func PutBuffer(buf []byte) {
	size := cap(buf)
	i := bits.Len32(uint32(size)) - 1
	if i < num && sizes[i] == size {
		pools[i].Put(buf)
	}
}