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