What are the Fastest Methods for Parsing Space-Separated Floats in C ?

How to Parse Space-Separated Floats in C Quickly

Parsing space-separated floats can be a time-consuming task, especially when dealing with large files. Traditional methods like using standard C streams can be slow. This article explores several efficient methods for parsing floats in C .

Boost Spirit

Boost Spirit is a powerful C library that provides advanced parsing capabilities. Despite its initial learning curve, Spirit offers fast and reliable parsing. Here's how to use it:

#include <boost/spirit/include/qi.hpp>

namespace qi = boost::spirit::qi;

int main() {
  std::string line = "134.32 3545.87 3425";

  double x, y, z;
  auto it = line.begin();
  bool success = qi::phrase_parse(it, line.end(), qi::double_ >> qi::double_ >> qi::double_, qi::blank, data);

  if (success) {
    std::cout << "Parsed values: " << x << " " << y << " " << z << std::endl;
  }

  return 0;
}

Memory Mapped Files

Memory-mapped files offer a faster way to read files into memory without the overhead of traditional I/O operations. This can significantly speed up parsing:

#include <iostream>
#include <fstream>
#include <sys/stat.h>
#include <sys/mman.h>

int main() {
  std::ifstream file("data.txt");
  struct stat statbuf;
  fstat(file.fileno(), &statbuf);

  // Memory-map the file
  char* data = static_cast<char*>(mmap(NULL, statbuf.st_size, PROT_READ, MAP_SHARED, file.fileno(), 0));

  // Iterate through the data to parse floats
  for (char* ptr = data; ptr < data + statbuf.st_size;) {
    double x, y, z;
    ptr = std::sscanf(ptr, "%f %f %f", &x, &y, &z);
    // Parse the float values and perform desired operations
  }

  // Unmap the file
  munmap(data, statbuf.st_size);

  return 0;
}

Benchmarks

Various parsing methods have been benchmarked to demonstrate their speed differences. Boost Spirit emerged as the fastest, followed by the memory-mapped file approach and the standard C streams. The exact performance may vary depending on the size and complexity of the data.

Conclusion

Parsing space-separated floats in C can be optimized using different techniques. Boost Spirit provides the highest performance, but requires more understanding of its parsing mechanisms. Memory-mapped files offer a middle ground, speeding up parsing while maintaining code simplicity. Traditional C streams remain a viable option, although slower in computation.

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