/// <summary>
/// Decode the length determinant
/// ITU-T X.691. 10.9. General rules for encoding a length determinant
/// </summary>
protected virtual int decodeLengthDeterminant(BitArrayInputStream stream)
{
skipAlignedBits(stream);
int result = stream.ReadByte();
if ((result & 0x80) == 0)
{
// NOTE 2. a) ("n" less than 128)
// a single octet containing "n" with bit 8 set to zero;
return(result);
}
else
{
// NOTE 2. b) ("n" less than 16K) two octets
// containing "n" with bit 8 of the first octet
// set to 1 and bit 7 set to zero;
result = (result & 0x3f) << 8;
result |= stream.ReadByte();
}
// WARNING! Large N doesn't supported NOW!
// NOTE 2. b) (large "n") a single octet containing a count "m"
// with bit 8 set to 1 and bit 7 set to 1.
// The count "m" is one to four, and the length indicates that
// a fragment of the material follows (a multiple "m" of 16K items).
// For all values of "m", the fragment is then followed
// by another length encoding for the remainder of the material.
return(result);
}
/// <summary>
/// Decode of the constrained whole number
/// ITU-T X.691. 10.5.
/// NOTE – (Tutorial) This subclause is referenced by other clauses,
/// and itself references earlier clauses for the production of
/// a nonnegative-binary-integer or a 2's-complement-binary-integer encoding.
/// </summary>
protected virtual long decodeConstraintNumber(long min, long max, BitArrayInputStream stream)
{
long result = 0;
long valueRange = max - min;
//!!!! int narrowedVal = value - min; !!!
int maxBitLen = PERCoderUtils.getMaxBitLength(valueRange);
if (valueRange == 0)
{
return(max);
}
// The rest of this Note addresses the ALIGNED variant.
if (valueRange > 0 && valueRange < 256)
{
/*
* 1. Where the range is less than or equal to 255, the value encodes
* into a bit-field of the minimum size for the range.
* 2. Where the range is exactly 256, the value encodes
* into a single octet octet-aligned bit-field.
*/
skipAlignedBits(stream);
result = stream.readBits(maxBitLen);
result += min;
}
else if (valueRange > 0 && valueRange < 65536)
{
/*
* 3. Where the range is 257 to 64K, the value encodes into
* a two octet octet-aligned bit-field.
*/
skipAlignedBits(stream);
result = stream.ReadByte() << 8;
result = (int)result | stream.ReadByte();
result += min;
}
else
{
/*
* 4. Where the range is greater than 64K, the range is ignored
* and the value encodes into an octet-aligned bit-field
* which is the minimum number of octets for the value.
* In this latter case, later procedures (see 10.9)
* also encode a length field (usually a single octet) to indicate
* the length of the encoding. For the other cases, the length
* of the encoding is independent of the value being encoded,
* and is not explicitly encoded.
*/
int intLen = decodeConstraintLengthDeterminant(1, CoderUtils.getPositiveIntegerLength(valueRange), stream);
skipAlignedBits(stream);
result = (int)decodeIntegerValueAsBytes(intLen, stream);
result += min;
}
return(result);
}
protected override long decodeConstraintNumber(long min, long max, BitArrayInputStream stream)
{
long result = 0;
long valueRange = max - min;
// !!! int narrowedVal = value - min; !!!
int maxBitLen = PERCoderUtils.getMaxBitLength(valueRange);
if (valueRange == 0)
{
return(max);
}
// For the UNALIGNED variant the value is always encoded in the minimum
// number of bits necessary to represent the range (defined in 10.5.3).
int currentBit = maxBitLen;
while (currentBit > 7)
{
currentBit -= 8;
result |= (uint)(stream.ReadByte() << currentBit);
}
if (currentBit > 0)
{
result |= (uint)stream.readBits(currentBit);
}
result += min;
return(result);
}
protected override long decodeConstraintNumber(long min, long max, BitArrayInputStream stream)
{
long result = 0;
long valueRange = max - min;
// !!! int narrowedVal = value - min; !!!
int maxBitLen = PERCoderUtils.getMaxBitLength(valueRange);
if (valueRange == 0)
{
return max;
}
//For the UNALIGNED variant the value is always encoded in the minimum
// number of bits necessary to represent the range (defined in 10.5.3).
int currentBit = maxBitLen;
while (currentBit > 7)
{
currentBit -= 8;
result |= (uint)(stream.ReadByte() << currentBit);
}
if (currentBit > 0)
{
result |= (uint)(stream.readBits(currentBit));
}
result += min;
return result;
}
/// <seealso cref="BitArrayInputStream.read()">
/// </seealso>
public virtual void testRead()
{
BitArrayInputStream stream = newStream();
int bt = stream.ReadByte();
Assert.Equals(0xAB, bt);
bt = stream.ReadByte();
Assert.Equals(0xCD, bt);
bt = stream.readBit();
Assert.Equals(1, bt);
bt = stream.readBit();
Assert.Equals(1, bt);
bt = stream.ReadByte();
Assert.Equals(0xBC, bt);
bt = stream.ReadByte();
Assert.Equals(0xCF, bt);
stream.skipUnreadedBits();
bt = stream.ReadByte();
Assert.Equals(0xDC, bt);
bt = stream.readBits(4);
Assert.Equals(0x0B, bt);
bt = stream.readBits(4);
Assert.Equals(0x0A, bt);
}