Function DoubleToBuffer

tensorflow/core/lib/strings/numbers.cc:182–211

static const double kDoublePrecisionCheckMax = DBL_MAX / 1.000000000000001;

size_t DoubleToBuffer(double value, char* buffer) {
  // DBL_DIG is 15 for IEEE-754 doubles, which are used on almost all
  // platforms these days.  Just in case some system exists where DBL_DIG
  // is significantly larger -- and risks overflowing our buffer -- we have
  // this assert.
  static_assert(DBL_DIG < 20, "DBL_DIG is too big");

  if (std::abs(value) <= kDoublePrecisionCheckMax) {
    int snprintf_result =
        snprintf(buffer, kFastToBufferSize, "%.*g", DBL_DIG, value);

    // The snprintf should never overflow because the buffer is significantly
    // larger than the precision we asked for.
    DCHECK(snprintf_result > 0 && snprintf_result < kFastToBufferSize);

    if (locale_independent_strtonum<double>(buffer, nullptr) == value) {
      // Round-tripping the string to double works; we're done.
      return snprintf_result;
    }
    // else: full precision formatting needed. Fall through.
  }

  int snprintf_result =
      snprintf(buffer, kFastToBufferSize, "%.*g", DBL_DIG + 2, value);

  // Should never overflow; see above.
  DCHECK(snprintf_result > 0 && snprintf_result < kFastToBufferSize);

  return snprintf_result;
}

namespace {
char SafeFirstChar(StringPiece str) {