text: #include "string_util.h"
  
  #include <array>
  #ifdef BENCHMARK_STL_ANDROID_GNUSTL
  #include <cerrno>
  #endif
  #include <cmath>
  #include <cstdarg>
  #include <cstdio>
  #include <memory>
  #include <sstream>
  
  #include "arraysize.h"
  
  namespace benchmark {
  namespace {
  
  // kilo, Mega, Giga, Tera, Peta, Exa, Zetta, Yotta.
  const char kBigSIUnits[] = "kMGTPEZY";
  // Kibi, Mebi, Gibi, Tebi, Pebi, Exbi, Zebi, Yobi.
  const char kBigIECUnits[] = "KMGTPEZY";
  // milli, micro, nano, pico, femto, atto, zepto, yocto.
  const char kSmallSIUnits[] = "munpfazy";
  
  // We require that all three arrays have the same size.
  static_assert(arraysize(kBigSIUnits) == arraysize(kBigIECUnits),
                "SI and IEC unit arrays must be the same size");
  static_assert(arraysize(kSmallSIUnits) == arraysize(kBigSIUnits),
                "Small SI and Big SI unit arrays must be the same size");
  
  static const int64_t kUnitsSize = arraysize(kBigSIUnits);
  
  void ToExponentAndMantissa(double val, double thresh, int precision,
                             double one_k, std::string* mantissa,
                             int64_t* exponent) {
    std::stringstream mantissa_stream;
  
    if (val < 0) {
      mantissa_stream << "-";
      val = -val;
    }
  
    // Adjust threshold so that it never excludes things which can't be rendered
    // in 'precision' digits.
    const double adjusted_threshold =
        std::max(thresh, 1.0 / std::pow(10.0, precision));
    const double big_threshold = adjusted_threshold * one_k;
    const double small_threshold = adjusted_threshold;
    // Values in ]simple_threshold,small_threshold[ will be printed as-is
    const double simple_threshold = 0.01;
  
    if (val > big_threshold) {
      // Positive powers
      double scaled = val;
      for (size_t i = 0; i < arraysize(kBigSIUnits); ++i) {
        scaled /= one_k;
        if (scaled <= big_threshold) {
          mantissa_stream << scaled;
          *exponent = i + 1;
          *mantissa = mantissa_stream.str();
          return;
        }
      }
      mantissa_stream << val;
      *exponent = 0;
    } else if (val < small_threshold) {
      // Negative powers
      if (val < simple_threshold) {
        double scaled = val;
        for (size_t i = 0; i < arraysize(kSmallSIUnits); ++i) {
          scaled *= one_k;
          if (scaled >= small_threshold) {
            mantissa_stream << scaled;
            *exponent = -static_cast<int64_t>(i + 1);
            *mantissa = mantissa_stream.str();
            return;
          }
        }
      }
      mantissa_stream << val;
      *exponent = 0;
    } else {
      mantissa_stream << val;
      *exponent = 0;
    }
    *mantissa = mantissa_stream.str();
  }
  
  std::string ExponentToPrefix(int64_t exponent, bool iec) {
    if (exponent == 0) return "";
  
    const int64_t index = (exponent > 0 ? exponent - 1 : -exponent - 1);
    if (index >= kUnitsSize) return "";
  
    const char* array =
        (exponent > 0 ? (iec ? kBigIECUnits : kBigSIUnits) : kSmallSIUnits);
    if (iec)
      return array[index] + std::string("i");
    else
      return std::string(1, array[index]);
  }
  
  std::string ToBinaryStringFullySpecified(double value, double threshold,
                                           int precision, double one_k = 1024.0) {
    std::string mantissa;
    int64_t exponent;
    ToExponentAndMantissa(value, threshold, precision, one_k, &mantissa,
                          &exponent);
    return mantissa + ExponentToPrefix(exponent, false);
  }
  
  }  // end namespace
  
  void AppendHumanReadable(int n, std::string* str) {
    std::stringstream ss;
    // Round down to the nearest SI prefix.
    ss << ToBinaryStringFullySpecified(n, 1.0, 0);
    *str += ss.str();
  }
  
  std::string HumanReadableNumber(double n, double one_k) {
    // 1.1 means that figures up to 1.1k should be shown with the next unit down;
    // this softens edge effects.
    // 1 means that we should show one decimal place of precision.
    return ToBinaryStringFullySpecified(n, 1.1, 1, one_k);
  }
  
  std::string StrFormatImp(const char* msg, va_list args) {
    // we might need a second shot at this, so pre-emptivly make a copy
    va_list args_cp;
    va_copy(args_cp, args);
  
    // TODO(ericwf): use std::array for first attempt to avoid one memory
    // allocation guess what the size might be
    std::array<char, 256> local_buff;
    std::size_t size = local_buff.size();
    // 2015-10-08: vsnprintf is used instead of snd::vsnprintf due to a limitation
    // in the android-ndk
    auto ret = vsnprintf(local_buff.data(), size, msg, args_cp);
  
    va_end(args_cp);
  
    // handle empty expansion
    if (ret == 0) return std::string{};
    if (static_cast<std::size_t>(ret) < size)
      return std::string(local_buff.data());
  
    // we did not provide a long enough buffer on our first attempt.
    // add 1 to size to account for null-byte in size cast to prevent overflow
    size = static_cast<std::size_t>(ret) + 1;
    auto buff_ptr = std::unique_ptr<char[]>(new char[size]);
    // 2015-10-08: vsnprintf is used instead of snd::vsnprintf due to a limitation
    // in the android-ndk
    ret = vsnprintf(buff_ptr.get(), size, msg, args);
    return std::string(buff_ptr.get());
  }
  
  std::string StrFormat(const char* format, ...) {
    va_list args;
    va_start(args, format);
    std::string tmp = StrFormatImp(format, args);
    va_end(args);
    return tmp;
  }
  
  #ifdef BENCHMARK_STL_ANDROID_GNUSTL
  /*
   * GNU STL in Android NDK lacks support for some C++11 functions, including
   * stoul, stoi, stod. We reimplement them here using C functions strtoul,
   * strtol, strtod. Note that reimplemented functions are in benchmark::
   * namespace, not std:: namespace.
   */
  unsigned long stoul(const std::string& str, size_t* pos, int base) {
    /* Record previous errno */
    const int oldErrno = errno;
    errno = 0;
  
    const char* strStart = str.c_str();
    char* strEnd = const_cast<char*>(strStart);
    const unsigned long result = strtoul(strStart, &strEnd, base);
  
    const int strtoulErrno = errno;
    /* Restore previous errno */
    errno = oldErrno;
  
    /* Check for errors and return */
    if (strtoulErrno == ERANGE) {
      throw std::out_of_range("stoul failed: " + str +
                              " is outside of range of unsigned long");
    } else if (strEnd == strStart || strtoulErrno != 0) {
      throw std::invalid_argument("stoul failed: " + str + " is not an integer");
    }
    if (pos != nullptr) {
      *pos = static_cast<size_t>(strEnd - strStart);
    }
    return result;
  }
  
  int stoi(const std::string& str, size_t* pos, int base) {
    /* Record previous errno */
    const int oldErrno = errno;
    errno = 0;
  
    const char* strStart = str.c_str();
    char* strEnd = const_cast<char*>(strStart);
    const long result = strtol(strStart, &strEnd, base);
  
    const int strtolErrno = errno;
    /* Restore previous errno */
    errno = oldErrno;
  
    /* Check for errors and return */
    if (strtolErrno == ERANGE || long(int(result)) != result) {
      throw std::out_of_range("stoul failed: " + str +
                              " is outside of range of int");
    } else if (strEnd == strStart || strtolErrno != 0) {
      throw std::invalid_argument("stoul failed: " + str + " is not an integer");
    }
    if (pos != nullptr) {
      *pos = static_cast<size_t>(strEnd - strStart);
    }
    return int(result);
  }
  
  double stod(const std::string& str, size_t* pos) {
    /* Record previous errno */
    const int oldErrno = errno;
    errno = 0;
  
    const char* strStart = str.c_str();
    char* strEnd = const_cast<char*>(strStart);
    const double result = strtod(strStart, &strEnd);
  
    /* Restore previous errno */
    const int strtodErrno = errno;
    errno = oldErrno;
  
    /* Check for errors and return */
    if (strtodErrno == ERANGE) {
      throw std::out_of_range("stoul failed: " + str +
                              " is outside of range of int");
    } else if (strEnd == strStart || strtodErrno != 0) {
      throw std::invalid_argument("stoul failed: " + str + " is not an integer");
    }
    if (pos != nullptr) {
      *pos = static_cast<size_t>(strEnd - strStart);
    }
    return result;
  }
  #endif
  
  }  // end namespace benchmark
  