bitmap.go

// Copyright (c) Roman Atachiants and contributors. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for details.

package bitmap

import (
	"math/bits"
	"unsafe"

	"github.com/klauspost/cpuid/v2"
)

const (
	isUnsupported = iota
	isAccelerated
	isAVX512
)

// Hardware contains the resolved acceleration level
var hardware = levelOf(cpuid.CPU)

// levelOf returns the hardware acceleration level
func levelOf(cpu cpuid.CPUInfo) int {
	switch {
	case cpu.Supports(cpuid.AVX512F) && cpu.Supports(cpuid.AVX512DQ) && cpu.Supports(cpuid.AVX512BW):
		return isAVX512
	case cpu.Supports(cpuid.AVX2) && cpu.Supports(cpuid.FMA3):
		return isAccelerated
	case cpu.Supports(cpuid.ASIMD):
		return isAccelerated
	default:
		return isUnsupported
	}
}

// Bitmap represents a scalar-backed bitmap index
type Bitmap []uint64

// Set sets the bit x in the bitmap and grows it if necessary.
func (dst *Bitmap) Set(x uint32) {
	blkAt := int(x >> 6)
	bitAt := int(x % 64)
	if size := len(*dst); blkAt >= size {
		dst.grow(blkAt)
	}

	(*dst)[blkAt] |= (1 << bitAt)
}

// Remove removes the bit x from the bitmap, but does not shrink it.
func (dst *Bitmap) Remove(x uint32) {
	if blkAt := int(x >> 6); blkAt < len(*dst) {
		bitAt := int(x % 64)
		(*dst)[blkAt] &^= (1 << bitAt)
	}
}

// Contains checks whether a value is contained in the bitmap or not.
func (dst Bitmap) Contains(x uint32) bool {
	blkAt := int(x >> 6)
	if size := len(dst); blkAt >= size {
		return false
	}

	bitAt := int(x % 64)
	return (dst[blkAt] & (1 << bitAt)) > 0
}

// Ones sets the entire bitmap to one.
func (dst Bitmap) Ones() {
	for i := 0; i < len(dst); i++ {
		dst[i] = 0xffffffffffffffff
	}
}

// Min get the smallest value stored in this bitmap, assuming the bitmap is not empty.
func (dst Bitmap) Min() (uint32, bool) {
	for blkAt, blk := range dst {
		if blk != 0x0 {
			return uint32(blkAt<<6 + bits.TrailingZeros64(blk)), true
		}
	}

	return 0, false
}

// Max get the largest value stored in this bitmap, assuming the bitmap is not empty.
func (dst Bitmap) Max() (uint32, bool) {
	var blk uint64
	for blkAt := len(dst) - 1; blkAt >= 0; blkAt-- {
		if blk = dst[blkAt]; blk != 0x0 {
			return uint32(blkAt<<6 + (63 - bits.LeadingZeros64(blk))), true
		}
	}
	return 0, false
}

// MinZero finds the first zero bit and returns its index, assuming the bitmap is not empty.
func (dst Bitmap) MinZero() (uint32, bool) {
	for blkAt, blk := range dst {
		if blk != 0xffffffffffffffff {
			return uint32(blkAt<<6 + bits.TrailingZeros64(^blk)), true
		}
	}
	return 0, false
}

// MaxZero get the last zero bit and return its index, assuming bitmap is not empty
func (dst Bitmap) MaxZero() (uint32, bool) {
	var blk uint64
	for blkAt := len(dst) - 1; blkAt >= 0; blkAt-- {
		if blk = dst[blkAt]; blk != 0xffffffffffffffff {
			return uint32(blkAt<<6 + (63 - bits.LeadingZeros64(^blk))), true
		}
	}
	return 0, false
}

// CountTo counts the number of elements in the bitmap up until the specified index. If until
// is math.MaxUint32, it will return the count. The count is non-inclusive of the index.
func (dst Bitmap) CountTo(until uint32) int {
	if len(dst) == 0 {
		return 0
	}

	if maxUntil := uint32(len(dst) << 6); until > maxUntil {
		until = maxUntil
	}

	// Figure out the index of the last block
	blkUntil := until >> 6
	bitUntil := until % 64

	// Count the bits right before the last block
	sum := dst[:blkUntil].Count()

	// Count the bits at the end
	if bitUntil > 0 {
		sum += bits.OnesCount64(dst[blkUntil] << (64 - uint64(bitUntil)))
	}
	return sum
}

// Grow grows the bitmap size until we reach the desired bit.
func (dst *Bitmap) Grow(desiredBit uint32) {
	dst.grow(int(desiredBit >> 6))
}

// grow grows the size of the bitmap until we reach the desired block offset
func (dst *Bitmap) grow(blkAt int) {
	if len(*dst) > blkAt {
		return
	}

	// If there's space, resize the slice without copying.
	if cap(*dst) > blkAt {
		*dst = (*dst)[:blkAt+1]
		return
	}

	old := *dst
	*dst = make(Bitmap, blkAt+1, resize(cap(old), blkAt+1))
	copy(*dst, old)
}

// shrink shrinks the size of the bitmap and resets to zero
func (dst *Bitmap) shrink(length int) {
	until := len(*dst)
	for i := length; i < until; i++ {
		(*dst)[i] = 0
	}

	// Trim without reallocating
	*dst = (*dst)[:length]
}

// minlen calculates the minimum length of all of the bitmaps
func minlen(a, b Bitmap, extra []Bitmap) int {
	size := minint(len(a), len(b))
	for _, v := range extra {
		if m := minint(len(a), len(v)); m < size {
			size = m
		}
	}
	return size
}

// maxlen calculates the maximum length of all of the bitmaps
func maxlen(a, b Bitmap, extra []Bitmap) int {
	size := maxint(len(a), len(b))
	for _, v := range extra {
		if m := maxint(len(a), len(v)); m > size {
			size = m
		}
	}
	return size
}

// maxint returns a maximum of two integers without branches.
func maxint(v1, v2 int) int {
	return v1 - ((v1 - v2) & ((v1 - v2) >> 31))
}

// minint returns a minimum of two integers without branches.
func minint(v1, v2 int) int {
	return v2 + ((v1 - v2) & ((v1 - v2) >> 31))
}

// resize calculates the new required capacity and a new index
func resize(capacity, v int) int {
	const threshold = 256
	if v < threshold {
		v |= v >> 1
		v |= v >> 2
		v |= v >> 4
		v |= v >> 8
		v |= v >> 16
		v++
		return int(v)
	}

	if capacity < threshold {
		capacity = threshold
	}

	for 0 < capacity && capacity < (v+1) {
		capacity += (capacity + 3*threshold) / 4
	}
	return capacity
}

// dimensionsOf returns a uint64 containing the packed dimensions
func dimensionsOf(n, m int) uint64 {
	return uint64(n) | (uint64(m) << 32)
}

// pointersOf returns a pointer to an array containing pointers to the
// first element of each bitmap and the maximum length of all bitmaps
func pointersOf(other Bitmap, extra []Bitmap) (unsafe.Pointer, int) {
	out := make([]unsafe.Pointer, len(extra)+1)
	out[0] = unsafe.Pointer(&other[0])
	max := 0

	for i := range extra {
		out[i+1] = unsafe.Pointer(&extra[i][0])
		if len(extra[i]) > max {
			max = len(extra[i])
		}
	}

	return unsafe.Pointer(&out[0]), max
}