BitStream.cc
1.31 KB
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#include <qpdf/BitStream.hh>
// See comments in bits.cc
#define BITS_READ 1
#include "bits.icc"
BitStream::BitStream(unsigned char const* p, int nbytes) :
start(p),
nbytes(nbytes)
{
reset();
}
void
BitStream::reset()
{
p = start;
bit_offset = 7;
if (static_cast<unsigned int>(nbytes) > static_cast<unsigned int>(-1) / 8)
{
throw std::runtime_error("array too large for bitstream");
}
bits_available = 8 * nbytes;
}
unsigned long long
BitStream::getBits(int nbits)
{
return read_bits(this->p, this->bit_offset,
this->bits_available, nbits);
}
long long
BitStream::getBitsSigned(int nbits)
{
unsigned long long bits = read_bits(this->p, this->bit_offset,
this->bits_available, nbits);
long long result = 0;
if (static_cast<long long>(bits) > 1 << (nbits - 1))
{
result = static_cast<long long>(bits - (1 << nbits));
}
else
{
result = static_cast<long long>(bits);
}
return result;
}
void
BitStream::skipToNextByte()
{
if (bit_offset != 7)
{
unsigned int bits_to_skip = bit_offset + 1;
if (bits_available < bits_to_skip)
{
throw std::logic_error(
"INTERNAL ERROR: overflow skipping to next byte in bitstream");
}
bit_offset = 7;
++p;
bits_available -= bits_to_skip;
}
}