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bitfield.go
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bitfield.go
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package main
import (
"math"
)
// Position represents a bit's location within the byte slice.
type Position struct {
Byte int32
Bit int32
}
// BitField implements bitfields for Bloom filters
type BitField struct {
Size int32
Bitfield []byte
}
// GetPos gets the position of a bit in a bitfield.
// Example:
// I want to get the position of the 100th bit. Since this is stored
// in a bytearray, one can't just do something like this:
// value = bitfield[100] // This will get the 100th byte, not bit!
// The 100th bit of a bytearray will be 4 bits into the 12th byte:
// >>> bitfield.getpos(100)
// Position(byte=12, bit=4)
func (bf *BitField) GetPos(position int32) Position {
var bytepos = int32(math.Ceil(float64(position)/8.0)) - 1
var bitpos = int32(position % 8)
if bitpos != 0 {
bitpos = 8 - bitpos
}
return Position{
Byte: bytepos,
Bit: bitpos,
}
}
// SetBit sets the bit at specified position to 1.
func (bf *BitField) SetBit(position int32) {
for position < 0 {
position += bf.Size
}
pos := bf.GetPos(position)
index := pos.Byte
if index == -1 {
index += int32(math.Ceil(float64(bf.Size) / 8.0))
}
bf.Bitfield[index] |= (0x01 << uint32(pos.Bit)) & 0xff
}
// UnsetBit sets the bit at specified position to 0.
func (bf *BitField) UnsetBit(position int32) {
for position < 0 {
position += bf.Size
}
pos := bf.GetPos(position)
index := pos.Byte
if index == -1 {
index += int32(math.Ceil(float64(bf.Size) / 8.0))
}
bf.Bitfield[index] &= ^(0x01 << uint32(pos.Bit)) & 0xff
}
// GetBit retrieves the contents of a bit at a specific location.
func (bf *BitField) GetBit(position int32) bool {
for position < 0 {
position += bf.Size
}
pos := bf.GetPos(position)
index := pos.Byte
if index == -1 {
index += int32(math.Ceil(float64(bf.Size) / 8.0))
}
contents := bf.Bitfield[index] & ((0x01 << uint32(pos.Bit)) & 0xff)
return !(contents == 0)
}
// Zero sets all bits to zero.
func (bf *BitField) Zero() {
byteSize := int32(math.Ceil(float64(bf.Size) / 8.0))
for pos := int32(0); pos < byteSize; pos++ {
bf.Bitfield[pos] = 0x00
}
}
// One sets all bits to one.
func (bf *BitField) One() {
byteSize := int32(math.Ceil(float64(bf.Size) / 8.0))
for pos := int32(0); pos < byteSize; pos++ {
bf.Bitfield[pos] = 0xff
}
}