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// Copyright 2020-2023 Daniel Lemire
// Copyright 2023 Matt Borland
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt
//
// Derivative of: https://github.com/fastfloat/fast_float
#ifndef BOOST_CHARCONV_DETAIL_FASTFLOAT_ASCII_NUMBER_HPP
#define BOOST_CHARCONV_DETAIL_FASTFLOAT_ASCII_NUMBER_HPP
#include <boost/charconv/detail/fast_float/float_common.hpp>
#include <cctype>
#include <cstdint>
#include <cstring>
#include <iterator>
namespace boost { namespace charconv { namespace detail { namespace fast_float {
// Next function can be micro-optimized, but compilers are entirely
// able to optimize it well.
template <typename UC>
BOOST_FORCEINLINE constexpr bool is_integer(UC c) noexcept {
return !(c > UC('9') || c < UC('0'));
}
BOOST_FORCEINLINE constexpr uint64_t byteswap(uint64_t val) {
return (val & 0xFF00000000000000) >> 56
| (val & 0x00FF000000000000) >> 40
| (val & 0x0000FF0000000000) >> 24
| (val & 0x000000FF00000000) >> 8
| (val & 0x00000000FF000000) << 8
| (val & 0x0000000000FF0000) << 24
| (val & 0x000000000000FF00) << 40
| (val & 0x00000000000000FF) << 56;
}
BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
uint64_t read_u64(const char *chars) {
if (cpp20_and_in_constexpr()) {
uint64_t val = 0;
for(int i = 0; i < 8; ++i) {
val |= uint64_t(*chars) << (i*8);
++chars;
}
return val;
}
uint64_t val;
::memcpy(&val, chars, sizeof(uint64_t));
#if BOOST_CHARCONV_FASTFLOAT_IS_BIG_ENDIAN == 1
// Need to read as-if the number was in little-endian order.
val = byteswap(val);
#endif
return val;
}
BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
void write_u64(uint8_t *chars, uint64_t val) {
if (cpp20_and_in_constexpr()) {
for(int i = 0; i < 8; ++i) {
*chars = uint8_t(val);
val >>= 8;
++chars;
}
return;
}
#if BOOST_CHARCONV_FASTFLOAT_IS_BIG_ENDIAN == 1
// Need to read as-if the number was in little-endian order.
val = byteswap(val);
#endif
::memcpy(chars, &val, sizeof(uint64_t));
}
// credit @aqrit
BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR14
uint32_t parse_eight_digits_unrolled(uint64_t val) {
constexpr uint64_t mask = 0x000000FF000000FF;
constexpr uint64_t mul1 = 0x000F424000000064; // 100 + (1000000ULL << 32)
constexpr uint64_t mul2 = 0x0000271000000001; // 1 + (10000ULL << 32)
val -= 0x3030303030303030;
val = (val * 10) + (val >> 8); // val = (val * 2561) >> 8;
val = (((val & mask) * mul1) + (((val >> 16) & mask) * mul2)) >> 32;
return uint32_t(val);
}
BOOST_FORCEINLINE constexpr
uint32_t parse_eight_digits_unrolled(const char16_t *) noexcept {
return 0;
}
BOOST_FORCEINLINE constexpr
uint32_t parse_eight_digits_unrolled(const char32_t *) noexcept {
return 0;
}
BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
uint32_t parse_eight_digits_unrolled(const char *chars) noexcept {
return parse_eight_digits_unrolled(read_u64(chars));
}
// credit @aqrit
BOOST_FORCEINLINE constexpr bool is_made_of_eight_digits_fast(uint64_t val) noexcept {
return !((((val + 0x4646464646464646) | (val - 0x3030303030303030)) & 0x8080808080808080));
}
BOOST_FORCEINLINE constexpr
bool is_made_of_eight_digits_fast(const char16_t *) noexcept {
return false;
}
BOOST_FORCEINLINE constexpr
bool is_made_of_eight_digits_fast(const char32_t *) noexcept {
return false;
}
BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
bool is_made_of_eight_digits_fast(const char *chars) noexcept {
return is_made_of_eight_digits_fast(read_u64(chars));
}
template <typename UC>
struct parsed_number_string_t {
int64_t exponent{0};
uint64_t mantissa{0};
UC const * lastmatch{nullptr};
bool negative{false};
bool valid{false};
bool too_many_digits{false};
// contains the range of the significant digits
span<const UC> integer{}; // non-nullable
span<const UC> fraction{}; // nullable
};
using byte_span = span<char>;
using parsed_number_string = parsed_number_string_t<char>;
// Assuming that you use no more than 19 digits, this will
// parse an ASCII string.
template <typename UC>
BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
parsed_number_string_t<UC> parse_number_string(UC const *p, UC const * pend, parse_options_t<UC> options) noexcept {
chars_format const fmt = options.format;
UC const decimal_point = options.decimal_point;
parsed_number_string_t<UC> answer;
answer.valid = false;
answer.too_many_digits = false;
answer.negative = (*p == UC('-'));
#ifdef BOOST_CHARCONV_FASTFLOAT_ALLOWS_LEADING_PLUS // disabled by default
if ((*p == UC('-')) || (*p == UC('+')))
#else
if (*p == UC('-')) // C++17 20.19.3.(7.1) explicitly forbids '+' sign here
#endif
{
++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;
}
}
UC const * const start_digits = p;
uint64_t i = 0; // an unsigned int avoids signed overflows (which are bad)
while ((p != pend) && is_integer(*p)) {
// a multiplication by 10 is cheaper than an arbitrary integer
// multiplication
i = 10 * i +
uint64_t(*p - UC('0')); // might overflow, we will handle the overflow later
++p;
}
UC const * const end_of_integer_part = p;
int64_t digit_count = int64_t(end_of_integer_part - start_digits);
answer.integer = span<const UC>(start_digits, size_t(digit_count));
int64_t exponent = 0;
if ((p != pend) && (*p == decimal_point)) {
++p;
UC const * 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.
if (std::is_same<UC,char>::value) {
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 - UC('0'));
++p;
i = i * 10 + digit; // in rare cases, this will overflow, but that's ok
}
exponent = before - p;
answer.fraction = span<const UC>(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 ((static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::scientific)) && (p != pend) && ((UC('e') == *p) || (UC('E') == *p))) {
UC const * location_of_e = p;
++p;
bool neg_exp = false;
if ((p != pend) && (UC('-') == *p)) {
neg_exp = true;
++p;
} else if ((p != pend) && (UC('+') == *p)) { // '+' on exponent is allowed by C++17 20.19.3.(7.1)
++p;
}
if ((p == pend) || !is_integer(*p)) {
if(!(static_cast<unsigned>(fmt) & static_cast<unsigned>(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 - UC('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((static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::scientific)) &&
!(static_cast<unsigned>(fmt) & static_cast<unsigned>(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.
UC const * start = start_digits;
while ((start != pend) && (*start == UC('0') || *start == decimal_point)) {
if(*start == UC('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;
UC const * int_end = p + answer.integer.len();
constexpr uint64_t minimal_nineteen_digit_integer{1000000000000000000};
while((i < minimal_nineteen_digit_integer) && (p != int_end)) {
i = i * 10 + uint64_t(*p - UC('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;
UC const * frac_end = p + answer.fraction.len();
while((i < minimal_nineteen_digit_integer) && (p != frac_end)) {
i = i * 10 + uint64_t(*p - UC('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;
}
}}}} // namespace s
#endif
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