internal/ceres/split.cc

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2015 Google Inc. All rights reserved.
// http://ceres-solver.org/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
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//   this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution.
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//   used to endorse or promote products derived from this software without
//   specific prior written permission.
//
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// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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// Author: keir@google.com (Keir Mierle)

#include "ceres/split.h"

#include <iterator>
#include <string>
#include <vector>

#include "ceres/internal/port.h"

namespace ceres {
namespace internal {

using std::string;
using std::vector;

// If we know how much to allocate for a vector of strings, we can allocate the
// vector<string> only once and directly to the right size. This saves in
// between 33-66 % of memory space needed for the result, and runs faster in the
// microbenchmarks.
//
// The reserve is only implemented for the single character delim.
//
// The implementation for counting is cut-and-pasted from
// SplitStringToIteratorUsing. I could have written my own counting iterator,
// and use the existing template function, but probably this is more clear and
// more sure to get optimized to reasonable code.
static int CalculateReserveForVector(const string& full, const char* delim) {
  int count = 0;
  if (delim[0] != '\0' && delim[1] == '\0') {
    // Optimize the common case where delim is a single character.
    char c = delim[0];
    const char* p = full.data();
    const char* end = p + full.size();
    while (p != end) {
      if (*p == c) {  // This could be optimized with hasless(v,1) trick.
        ++p;
      } else {
        while (++p != end && *p != c) {
          // Skip to the next occurence of the delimiter.
        }
        ++count;
      }
    }
  }
  return count;
}

template <typename StringType, typename ITR>
static inline void SplitStringToIteratorUsing(const StringType& full,
                                              const char* delim,
                                              ITR& result) {
  // Optimize the common case where delim is a single character.
  if (delim[0] != '\0' && delim[1] == '\0') {
    char c = delim[0];
    const char* p = full.data();
    const char* end = p + full.size();
    while (p != end) {
      if (*p == c) {
        ++p;
      } else {
        const char* start = p;
        while (++p != end && *p != c) {
          // Skip to the next occurence of the delimiter.
        }
        *result++ = StringType(start, p - start);
      }
    }
    return;
  }

  string::size_type begin_index, end_index;
  begin_index = full.find_first_not_of(delim);
  while (begin_index != string::npos) {
    end_index = full.find_first_of(delim, begin_index);
    if (end_index == string::npos) {
      *result++ = full.substr(begin_index);
      return;
    }
    *result++ = full.substr(begin_index, (end_index - begin_index));
    begin_index = full.find_first_not_of(delim, end_index);
  }
}

void SplitStringUsing(const string& full,
                      const char* delim,
                      vector<string>* result) {
  result->reserve(result->size() + CalculateReserveForVector(full, delim));
  std::back_insert_iterator<vector<string>> it(*result);
  SplitStringToIteratorUsing(full, delim, it);
}

}  // namespace internal
}  // namespace ceres