osrm-backend/src/engine/polyline_compressor.cpp
2024-06-22 20:04:32 +02:00

60 lines
1.8 KiB
C++

#include "engine/polyline_compressor.hpp"
#include <algorithm>
#include <boost/assert.hpp>
#include <climits>
#include <cmath>
#include <cstddef>
#include <cstdlib>
namespace osrm::engine::detail // anonymous to keep TU local
{
void encode(int number_to_encode, std::string &output)
{
if (number_to_encode < 0)
{
const unsigned binary = std::llabs(number_to_encode);
const unsigned twos = (~binary) + 1u;
const unsigned shl = twos << 1u;
number_to_encode = static_cast<int>(~shl);
}
else
{
number_to_encode <<= 1u;
}
while (number_to_encode >= 0x20)
{
const int next_value = (0x20 | (number_to_encode & 0x1f)) + 63;
output += static_cast<char>(next_value);
number_to_encode >>= 5;
}
number_to_encode += 63;
output += static_cast<char>(number_to_encode);
}
// https://developers.google.com/maps/documentation/utilities/polylinealgorithm
std::int32_t decode_polyline_integer(std::string::const_iterator &first,
std::string::const_iterator last)
{
// varint coding parameters
const std::uint32_t bits_in_chunk = 5;
const std::uint32_t continuation_bit = 1 << bits_in_chunk;
const std::uint32_t chunk_mask = (1 << bits_in_chunk) - 1;
std::uint32_t result = 0;
for (std::uint32_t value = continuation_bit, shift = 0;
(value & continuation_bit) && (shift < CHAR_BIT * sizeof(result) - 1) && first != last;
++first, shift += bits_in_chunk)
{
value = *first - 63; // convert ASCII coding [?..~] to an integer [0..63]
result |= (value & chunk_mask) << shift;
}
// change "zig-zag" sign coding to two's complement
result = ((result & 1) == 1) ? ~(result >> 1) : (result >> 1);
return static_cast<std::int32_t>(result);
}
} // namespace osrm::engine::detail