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#ifndef __BITS_FUNCTIONS_HH__
#define __BITS_FUNCTIONS_HH__
#include <qpdf/Pipeline.hh>
#include <qpdf/QTC.hh>
#include <qpdf/QUtil.hh>
#include <algorithm>
#include <stdexcept>
// This file is #included by specific source files, which must define
// certain preprocessor symbols. These functions may be run at places
// where the function call overhead from test coverage testing would
// be too high. Therefore, we make the test coverage cases conditional
// upon a preprocessor symbol. Library code includes this file without
// BITS_TESTING, and the specially designed test code that fully
// exercises this code includes with the symbol defined.
#ifdef BITS_READ
static unsigned long long
read_bits(
unsigned char const*& p,
size_t& bit_offset,
size_t& bits_available,
size_t bits_wanted)
{
// View p as a stream of bits:
// 76543210 76543210 ....
// bit_offset is the bit number within the first byte that marks
// the first bit that we would read.
if (bits_wanted > bits_available) {
throw std::runtime_error(
"overflow reading bit stream: wanted = " +
QUtil::uint_to_string(bits_wanted) +
"; available = " + QUtil::uint_to_string(bits_available));
}
if (bits_wanted > 32) {
throw std::out_of_range("read_bits: too many bits requested");
}
unsigned long result = 0;
# ifdef BITS_TESTING
if (bits_wanted == 0) {
QTC::TC("libtests", "bits zero bits wanted");
}
# endif
while (bits_wanted > 0) {
// Grab bits from the first byte clearing anything before
// bit_offset.
unsigned char byte =
static_cast<unsigned char>(*p & ((1U << (bit_offset + 1U)) - 1U));
// There are bit_offset + 1 bits available in the first byte.
size_t to_copy = std::min(bits_wanted, bit_offset + 1);
size_t leftover = (bit_offset + 1) - to_copy;
# ifdef BITS_TESTING
QTC::TC(
"libtests",
"bits bit_offset",
((bit_offset == 0) ? 0
: (bit_offset == 7) ? 1
: 2));
QTC::TC("libtests", "bits leftover", (leftover > 0) ? 1 : 0);
# endif
// Right shift so that all the bits we want are right justified.
byte = static_cast<unsigned char>(byte >> leftover);
// Copy the bits into result
result <<= to_copy;
result |= byte;
// Update pointers
if (leftover) {
bit_offset = leftover - 1;
} else {
bit_offset = 7;
++p;
}
bits_wanted -= to_copy;
bits_available -= to_copy;
# ifdef BITS_TESTING
QTC::TC(
"libtests",
"bits iterations",
((bits_wanted > 8) ? 0
: (bits_wanted > 0) ? 1
: 2));
# endif
}
return result;
}
#endif
#ifdef BITS_WRITE
static void
write_bits(
unsigned char& ch,
size_t& bit_offset,
unsigned long long val,
size_t bits,
Pipeline* pipeline)
{
if (bits > 32) {
throw std::out_of_range("write_bits: too many bits requested");
}
// bit_offset + 1 is the number of bits left in ch
# ifdef BITS_TESTING
if (bits == 0) {
QTC::TC("libtests", "bits write zero bits");
}
# endif
while (bits > 0) {
size_t bits_to_write = std::min(bits, bit_offset + 1);
unsigned char newval = static_cast<unsigned char>(
(val >> (bits - bits_to_write)) & ((1U << bits_to_write) - 1));
size_t bits_left_in_ch = bit_offset + 1 - bits_to_write;
newval = static_cast<unsigned char>(newval << bits_left_in_ch);
ch |= newval;
if (bits_left_in_ch == 0) {
# ifdef BITS_TESTING
QTC::TC("libtests", "bits write pipeline");
# endif
pipeline->write(&ch, 1);
bit_offset = 7;
ch = 0;
} else {
# ifdef BITS_TESTING
QTC::TC("libtests", "bits write leftover");
# endif
bit_offset -= bits_to_write;
}
bits -= bits_to_write;
# ifdef BITS_TESTING
QTC::TC(
"libtests",
"bits write iterations",
((bits > 8) ? 0
: (bits > 0) ? 1
: 2));
# endif
}
}
#endif
#endif // __BITS_FUNCTIONS_HH__
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