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// Copyright 2021 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package bitmap provides the implementation of bitmap.
package bitmap
import (
"math"
"math/bits"
)
// Bitmap implements an efficient bitmap.
//
// +stateify savable
type Bitmap struct {
// numOnes is the number of ones in the bitmap.
numOnes uint32
// bitBlock holds the bits. The type of bitBlock is uint64 which means
// each number in bitBlock contains 64 entries.
bitBlock []uint64
}
// BitmapWithSize create a new empty Bitmap.
func BitmapWithSize(size uint32) Bitmap {
b := Bitmap{}
bSize := (size + 63) / 64
b.bitBlock = make([]uint64, bSize)
return b
}
// IsEmpty verifies whether the Bitmap is empty.
func (b *Bitmap) IsEmpty() bool {
return b.numOnes == 0
}
// Minimum return the smallest value in the Bitmap.
func (b *Bitmap) Minimum() uint32 {
for i := 0; i < len(b.bitBlock); i++ {
if w := b.bitBlock[i]; w != 0 {
r := bits.TrailingZeros64(w)
return uint32(r + i*64)
}
}
return math.MaxInt32
}
// Maximum return the largest value in the Bitmap.
func (b *Bitmap) Maximum() uint32 {
for i := len(b.bitBlock) - 1; i >= 0; i-- {
if w := b.bitBlock[i]; w != 0 {
r := bits.LeadingZeros64(w)
return uint32(i*64 + 63 - r)
}
}
return uint32(0)
}
// Add add i to the Bitmap.
func (b *Bitmap) Add(i uint32) {
blockNum, mask := i/64, uint64(1)<<(i%64)
// if blockNum is out of range, extend b.bitBlock
if x, y := int(blockNum), len(b.bitBlock); x >= y {
b.bitBlock = append(b.bitBlock, make([]uint64, x-y+1)...)
}
oldBlock := b.bitBlock[blockNum]
newBlock := oldBlock | mask
if oldBlock != newBlock {
b.bitBlock[blockNum] = newBlock
b.numOnes++
}
}
// Remove i from the Bitmap.
func (b *Bitmap) Remove(i uint32) {
blockNum, mask := i/64, uint64(1)<<(i%64)
oldBlock := b.bitBlock[blockNum]
newBlock := oldBlock &^ mask
if oldBlock != newBlock {
b.bitBlock[blockNum] = newBlock
b.numOnes--
}
}
// Clone the Bitmap.
func (b *Bitmap) Clone() Bitmap {
bitmap := Bitmap{b.numOnes, make([]uint64, len(b.bitBlock))}
copy(bitmap.bitBlock, b.bitBlock[:])
return bitmap
}
// countOnesForBlocks count all 1 bits within b.bitBlock of begin and that of end.
// The begin block and end block are inclusive.
func (b *Bitmap) countOnesForBlocks(begin, end uint32) uint64 {
ones := uint64(0)
beginBlock := begin / 64
endBlock := end / 64
for i := beginBlock; i <= endBlock; i++ {
ones += uint64(bits.OnesCount64(b.bitBlock[i]))
}
return ones
}
// countOnesForAllBlocks count all 1 bits in b.bitBlock.
func (b *Bitmap) countOnesForAllBlocks() uint64 {
ones := uint64(0)
for i := 0; i < len(b.bitBlock); i++ {
ones += uint64(bits.OnesCount64(b.bitBlock[i]))
}
return ones
}
// flipRange flip the bits within range (begin and end). begin is inclusive and end is exclusive.
func (b *Bitmap) flipRange(begin, end uint32) {
end--
beginBlock := begin / 64
endBlock := end / 64
if beginBlock == endBlock {
b.bitBlock[endBlock] ^= ((^uint64(0) << uint(begin%64)) & ((uint64(1) << (uint(end) % 64 + 1))-1))
} else {
b.bitBlock[beginBlock] ^= ^(^uint64(0) << uint(begin%64))
for i := beginBlock; i < endBlock; i++ {
b.bitBlock[i] = ^b.bitBlock[i]
}
b.bitBlock[endBlock] ^= ((uint64(1) << (uint(end) % 64 + 1))-1)
}
}
// clearRange clear the bits within range (begin and end). begin is inclusive and end is exclusive.
func (b *Bitmap) clearRange(begin, end uint32) {
end--
beginBlock := begin / 64
endBlock := end / 64
if beginBlock == endBlock {
b.bitBlock[beginBlock] &= (((uint64(1) << uint(begin%64)) - 1) | ^((uint64(1) << (uint(end) % 64 + 1)) - 1))
} else {
b.bitBlock[beginBlock] &= ((uint64(1) << uint(begin%64)) - 1)
for i := beginBlock + 1; i < endBlock; i++ {
b.bitBlock[i] &= ^b.bitBlock[i]
}
b.bitBlock[endBlock] &= ^((uint64(1) << (uint(end) % 64 + 1)) - 1)
}
}
// ClearRange clear bits within range (begin and end) for the Bitmap. begin is inclusive and end is exclusive.
func (b *Bitmap) ClearRange(begin, end uint32) {
blockRange := end/64 - begin/64
// When the number of cleared blocks is larger than half of the length of b.bitBlock,
// counting 1s for the entire bitmap has better performance.
if blockRange > uint32(len(b.bitBlock)/2) {
b.clearRange(begin, end)
b.numOnes = uint32(b.countOnesForAllBlocks())
} else {
oldRangeOnes := b.countOnesForBlocks(begin, end)
b.clearRange(begin, end)
newRangeOnes := b.countOnesForBlocks(begin, end)
b.numOnes += uint32(newRangeOnes - oldRangeOnes)
}
}
// FlipRange flip bits within range (begin and end) for the Bitmap. begin is inclusive and end is exclusive.
func (b *Bitmap) FlipRange(begin, end uint32) {
blockRange := end/64 - begin/64
// When the number of flipped blocks is larger than half of the length of b.bitBlock,
// counting 1s for the entire bitmap has better performance.
if blockRange > uint32(len(b.bitBlock)/2) {
b.flipRange(begin, end)
b.numOnes = uint32(b.countOnesForAllBlocks())
} else {
oldRangeOnes := b.countOnesForBlocks(begin, end)
b.flipRange(begin, end)
newRangeOnes := b.countOnesForBlocks(begin, end)
b.numOnes += uint32(newRangeOnes - oldRangeOnes)
}
}
// ToSlice transform the Bitmap into slice. For example, a bitmap of [0, 1, 0, 1]
// will return the slice [1, 3].
func (b *Bitmap) ToSlice() []uint32 {
bitmapSlice := make([]uint32, 0, b.numOnes)
// base is the start number of a bitBlock
base := 0
for i := 0; i < len(b.bitBlock); i++ {
bitBlock := b.bitBlock[i]
// Iterate through all the numbers held by this bit block.
for bitBlock != 0 {
// Extract the lowest set 1 bit.
j := bitBlock & -bitBlock
// Interpret the bit as the in32 number it represents and add it to result.
bitmapSlice = append(bitmapSlice, uint32((base + int(bits.OnesCount64(j - 1)))))
bitBlock ^= j
}
base += 64
}
return bitmapSlice
}
// GetNumOnes return the the number of ones in the Bitmap.
func (b *Bitmap) GetNumOnes() uint32 {
return b.numOnes
}
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