in include/ylt/standalone/iguana/detail/fast_float.h [2440:2600]
fastfloat_really_inline parsed_number_string parse_number_string(
const char* p, const char* pend, parse_options options) noexcept {
const chars_format fmt = options.format;
const char decimal_point = options.decimal_point;
parsed_number_string answer;
answer.valid = false;
answer.too_many_digits = false;
answer.negative = (*p == '-');
if (*p == '-') { // C++17 20.19.3.(7.1) explicitly forbids '+' sign here
++p;
if (p == pend) {
return answer;
}
if (!is_integer(*p) &&
(*p !=
decimal_point)) { // a sign must be followed by an integer or the dot
return answer;
}
}
const char* const start_digits = p;
uint64_t i = 0; // an unsigned int avoids signed overflows (which are bad)
while ((std::distance(p, pend) >= 8) && is_made_of_eight_digits_fast(p)) {
i = i * 100000000 +
parse_eight_digits_unrolled(
p); // in rare cases, this will overflow, but that's ok
p += 8;
}
while ((p != pend) && is_integer(*p)) {
// a multiplication by 10 is cheaper than an arbitrary integer
// multiplication
i = 10 * i +
uint64_t(*p -
'0'); // might overflow, we will handle the overflow later
++p;
}
const char* const end_of_integer_part = p;
int64_t digit_count = int64_t(end_of_integer_part - start_digits);
answer.integer = byte_span(start_digits, size_t(digit_count));
int64_t exponent = 0;
if ((p != pend) && (*p == decimal_point)) {
++p;
const char* before = p;
// can occur at most twice without overflowing, but let it occur more, since
// for integers with many digits, digit parsing is the primary bottleneck.
while ((std::distance(p, pend) >= 8) && is_made_of_eight_digits_fast(p)) {
i = i * 100000000 +
parse_eight_digits_unrolled(
p); // in rare cases, this will overflow, but that's ok
p += 8;
}
while ((p != pend) && is_integer(*p)) {
uint8_t digit = uint8_t(*p - '0');
++p;
i = i * 10 + digit; // in rare cases, this will overflow, but that's ok
}
exponent = before - p;
answer.fraction = byte_span(before, size_t(p - before));
digit_count -= exponent;
}
// we must have encountered at least one integer!
if (digit_count == 0) {
return answer;
}
int64_t exp_number = 0; // explicit exponential part
if ((fmt & chars_format::scientific) && (p != pend) &&
(('e' == *p) || ('E' == *p))) {
const char* location_of_e = p;
++p;
bool neg_exp = false;
if ((p != pend) && ('-' == *p)) {
neg_exp = true;
++p;
}
else if ((p != pend) &&
('+' ==
*p)) { // '+' on exponent is allowed by C++17 20.19.3.(7.1)
++p;
}
if ((p == pend) || !is_integer(*p)) {
if (!(fmt & chars_format::fixed)) {
// We are in error.
return answer;
}
// Otherwise, we will be ignoring the 'e'.
p = location_of_e;
}
else {
while ((p != pend) && is_integer(*p)) {
uint8_t digit = uint8_t(*p - '0');
if (exp_number < 0x10000000) {
exp_number = 10 * exp_number + digit;
}
++p;
}
if (neg_exp) {
exp_number = -exp_number;
}
exponent += exp_number;
}
}
else {
// If it scientific and not fixed, we have to bail out.
if ((fmt & chars_format::scientific) && !(fmt & chars_format::fixed)) {
return answer;
}
}
answer.lastmatch = p;
answer.valid = true;
// If we frequently had to deal with long strings of digits,
// we could extend our code by using a 128-bit integer instead
// of a 64-bit integer. However, this is uncommon.
//
// We can deal with up to 19 digits.
if (digit_count > 19) { // this is uncommon
// It is possible that the integer had an overflow.
// We have to handle the case where we have 0.0000somenumber.
// We need to be mindful of the case where we only have zeroes...
// E.g., 0.000000000...000.
const char* start = start_digits;
while ((start != pend) && (*start == '0' || *start == decimal_point)) {
if (*start == '0') {
digit_count--;
}
start++;
}
if (digit_count > 19) {
answer.too_many_digits = true;
// Let us start again, this time, avoiding overflows.
// We don't need to check if is_integer, since we use the
// pre-tokenized spans from above.
i = 0;
p = answer.integer.ptr;
const char* int_end = p + answer.integer.len();
const uint64_t minimal_nineteen_digit_integer{1000000000000000000};
while ((i < minimal_nineteen_digit_integer) && (p != int_end)) {
i = i * 10 + uint64_t(*p - '0');
++p;
}
if (i >= minimal_nineteen_digit_integer) { // We have a big integers
exponent = end_of_integer_part - p + exp_number;
}
else { // We have a value with a fractional component.
p = answer.fraction.ptr;
const char* frac_end = p + answer.fraction.len();
while ((i < minimal_nineteen_digit_integer) && (p != frac_end)) {
i = i * 10 + uint64_t(*p - '0');
++p;
}
exponent = answer.fraction.ptr - p + exp_number;
}
// We have now corrected both exponent and i, to a truncated value
}
}
answer.exponent = exponent;
answer.mantissa = i;
return answer;
}