SabreTools/SabreTools.Compression
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Add endian reads for bits

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This commit is contained in:
Matt Nadareski
2023-09-21 22:20:57 -04:00
parent 47691d2034
commit 81eab984fb
1 changed files with 44 additions and 27 deletions
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71
BitStream.cs
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@@ -47,36 +47,16 @@ namespace SabreTools.Compression
}
/// <summary>
/// Read a single bit, if possible
/// Read a single bit with MSB as the leftmost bit, if possible
/// </summary>
/// <returns>The next bit encoded in a byte, null on error or end of stream</returns>
public byte? ReadBit()
{
// If we reached the end of the stream
if (_source.Position >= _source.Length)
return null;
public byte? ReadBitMSB() => ReadBitInternal(true);
// If we don't have a value cached
if (_lastRead == null)
{
// Read the next byte, if possible
_lastRead = ReadSourceByte();
if (_lastRead == null)
return null;
// Reset the bit index
_bitIndex = 0;
}
// Get the value by bit-shifting
int value = (_lastRead.Value >> _bitIndex++) & 0x01;
// Reset the byte if we're at the end
if (_bitIndex >= 8)
Discard();
return (byte)value;
}
/// <summary>
/// Read a single bit with LSB as the leftmost bit, if possible
/// </summary>
/// <returns>The next bit encoded in a byte, null on error or end of stream</returns>
public byte? ReadBitLSB() => ReadBitInternal(false);
/// <summary>
/// Read a full byte, if possible
@@ -170,6 +150,43 @@ namespace SabreTools.Compression
throw new NotImplementedException();
}
/// <summary>
/// Read a single bit, if possible
/// </summary>
/// <param name="msb">True if the value should be read MSB, false for LSB</param>
/// <returns>The next bit encoded in a byte, null on error or end of stream</returns>
private byte? ReadBitInternal(bool msb)
{
// If we reached the end of the stream
if (_source.Position >= _source.Length)
return null;
// If we don't have a value cached
if (_lastRead == null)
{
// Read the next byte, if possible
_lastRead = ReadSourceByte();
if (_lastRead == null)
return null;
// Reset the bit index
_bitIndex = 0;
}
// Get the value by bit-shifting
int value;
if (msb)
value = (_lastRead.Value >> _bitIndex++) & 0x01;
else
value = (_lastRead.Value >> (7 - _bitIndex++)) & 0x01;
// Reset the byte if we're at the end
if (_bitIndex >= 8)
Discard();
return (byte)value;
}
/// <summary>
/// Read a single byte from the underlying stream, if possible
/// </summary>