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mirror of https://github.com/OpenDiablo2/OpenDiablo2 synced 2024-11-14 00:06:45 -05:00
OpenDiablo2/d2common/bitmuncher.go
2020-01-26 00:39:13 -05:00

86 lines
1.7 KiB
Go

package d2common
type BitMuncher struct {
data []byte
Offset int
BitsRead int
}
func CreateBitMuncher(data []byte, offset int) *BitMuncher {
return &BitMuncher{
data: data,
Offset: offset,
BitsRead: 0,
}
}
func CopyBitMuncher(source *BitMuncher) *BitMuncher {
return &BitMuncher{
source.data,
source.Offset,
0,
}
}
func (v *BitMuncher) GetBit() uint32 {
result := uint32(v.data[v.Offset/8]>>uint(v.Offset%8)) & 0x01
v.Offset++
v.BitsRead++
return result
}
func (v *BitMuncher) SkipBits(bits int) {
v.Offset += bits
v.BitsRead += bits
}
func (v *BitMuncher) GetByte() byte {
return byte(v.GetBits(8))
}
func (v *BitMuncher) GetInt32() int32 {
return v.MakeSigned(v.GetBits(32), 32)
}
func (v *BitMuncher) GetUInt32() uint32 {
return v.GetBits(32)
}
func (v *BitMuncher) GetBits(bits int) uint32 {
if bits == 0 {
return 0
}
result := uint32(0)
for i := 0; i < bits; i++ {
result |= v.GetBit() << uint(i)
}
return result
}
func (v *BitMuncher) GetSignedBits(bits int) int {
return int(v.MakeSigned(v.GetBits(bits), bits))
}
func (v *BitMuncher) MakeSigned(value uint32, bits int) int32 {
if bits == 0 {
return 0
}
// If its a single bit, a value of 1 is -1 automagically
if bits == 1 {
return -int32(value)
}
// If there is no sign bit, return the value as is
if (value & (1 << uint(bits-1))) == 0 {
return int32(value)
}
// We need to extend the signed bit out so that the negative value representation still works with the 2s compliment rule.
result := uint32(4294967295)
for i := byte(0); i < byte(bits); i++ {
if ((value >> uint(i)) & 1) == 0 {
result -= uint32(1 << uint(i))
}
}
// Force casting to a signed value
return int32(result)
}