289 lines
9.5 KiB
C++
289 lines
9.5 KiB
C++
// Copyright 2020-2023 Daniel Lemire
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// Copyright 2023 Matt Borland
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// Distributed under the Boost Software License, Version 1.0.
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// https://www.boost.org/LICENSE_1_0.txt
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//
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// Derivative of: https://github.com/fastfloat/fast_float
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#ifndef BOOST_CHARCONV_DETAIL_FASTFLOAT_ASCII_NUMBER_HPP
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#define BOOST_CHARCONV_DETAIL_FASTFLOAT_ASCII_NUMBER_HPP
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#include <boost/charconv/detail/fast_float/float_common.hpp>
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#include <cctype>
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#include <cstdint>
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#include <cstring>
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#include <iterator>
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namespace boost { namespace charconv { namespace detail { namespace fast_float {
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// Next function can be micro-optimized, but compilers are entirely
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// able to optimize it well.
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template <typename UC>
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BOOST_FORCEINLINE constexpr bool is_integer(UC c) noexcept {
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return !(c > UC('9') || c < UC('0'));
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}
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BOOST_FORCEINLINE constexpr uint64_t byteswap(uint64_t val) {
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return (val & 0xFF00000000000000) >> 56
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| (val & 0x00FF000000000000) >> 40
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| (val & 0x0000FF0000000000) >> 24
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| (val & 0x000000FF00000000) >> 8
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| (val & 0x00000000FF000000) << 8
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| (val & 0x0000000000FF0000) << 24
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| (val & 0x000000000000FF00) << 40
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| (val & 0x00000000000000FF) << 56;
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}
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BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
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uint64_t read_u64(const char *chars) {
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if (cpp20_and_in_constexpr()) {
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uint64_t val = 0;
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for(int i = 0; i < 8; ++i) {
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val |= uint64_t(*chars) << (i*8);
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++chars;
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}
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return val;
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}
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uint64_t val;
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::memcpy(&val, chars, sizeof(uint64_t));
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#if BOOST_CHARCONV_FASTFLOAT_IS_BIG_ENDIAN == 1
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// Need to read as-if the number was in little-endian order.
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val = byteswap(val);
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#endif
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return val;
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}
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BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
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void write_u64(uint8_t *chars, uint64_t val) {
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if (cpp20_and_in_constexpr()) {
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for(int i = 0; i < 8; ++i) {
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*chars = uint8_t(val);
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val >>= 8;
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++chars;
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}
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return;
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}
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#if BOOST_CHARCONV_FASTFLOAT_IS_BIG_ENDIAN == 1
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// Need to read as-if the number was in little-endian order.
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val = byteswap(val);
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#endif
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::memcpy(chars, &val, sizeof(uint64_t));
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}
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// credit @aqrit
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BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR14
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uint32_t parse_eight_digits_unrolled(uint64_t val) {
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constexpr uint64_t mask = 0x000000FF000000FF;
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constexpr uint64_t mul1 = 0x000F424000000064; // 100 + (1000000ULL << 32)
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constexpr uint64_t mul2 = 0x0000271000000001; // 1 + (10000ULL << 32)
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val -= 0x3030303030303030;
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val = (val * 10) + (val >> 8); // val = (val * 2561) >> 8;
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val = (((val & mask) * mul1) + (((val >> 16) & mask) * mul2)) >> 32;
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return uint32_t(val);
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}
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BOOST_FORCEINLINE constexpr
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uint32_t parse_eight_digits_unrolled(const char16_t *) noexcept {
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return 0;
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}
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BOOST_FORCEINLINE constexpr
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uint32_t parse_eight_digits_unrolled(const char32_t *) noexcept {
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return 0;
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}
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BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
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uint32_t parse_eight_digits_unrolled(const char *chars) noexcept {
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return parse_eight_digits_unrolled(read_u64(chars));
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}
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// credit @aqrit
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BOOST_FORCEINLINE constexpr bool is_made_of_eight_digits_fast(uint64_t val) noexcept {
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return !((((val + 0x4646464646464646) | (val - 0x3030303030303030)) & 0x8080808080808080));
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}
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BOOST_FORCEINLINE constexpr
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bool is_made_of_eight_digits_fast(const char16_t *) noexcept {
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return false;
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}
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BOOST_FORCEINLINE constexpr
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bool is_made_of_eight_digits_fast(const char32_t *) noexcept {
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return false;
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}
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BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
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bool is_made_of_eight_digits_fast(const char *chars) noexcept {
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return is_made_of_eight_digits_fast(read_u64(chars));
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}
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template <typename UC>
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struct parsed_number_string_t {
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int64_t exponent{0};
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uint64_t mantissa{0};
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UC const * lastmatch{nullptr};
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bool negative{false};
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bool valid{false};
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bool too_many_digits{false};
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// contains the range of the significant digits
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span<const UC> integer{}; // non-nullable
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span<const UC> fraction{}; // nullable
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};
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using byte_span = span<char>;
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using parsed_number_string = parsed_number_string_t<char>;
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// Assuming that you use no more than 19 digits, this will
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// parse an ASCII string.
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template <typename UC>
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BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
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parsed_number_string_t<UC> parse_number_string(UC const *p, UC const * pend, parse_options_t<UC> options) noexcept {
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chars_format const fmt = options.format;
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UC const decimal_point = options.decimal_point;
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parsed_number_string_t<UC> answer;
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answer.valid = false;
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answer.too_many_digits = false;
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answer.negative = (*p == UC('-'));
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#ifdef BOOST_CHARCONV_FASTFLOAT_ALLOWS_LEADING_PLUS // disabled by default
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if ((*p == UC('-')) || (*p == UC('+')))
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#else
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if (*p == UC('-')) // C++17 20.19.3.(7.1) explicitly forbids '+' sign here
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#endif
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{
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++p;
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if (p == pend) {
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return answer;
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}
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if (!is_integer(*p) && (*p != decimal_point)) { // a sign must be followed by an integer or the dot
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return answer;
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}
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}
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UC const * const start_digits = p;
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uint64_t i = 0; // an unsigned int avoids signed overflows (which are bad)
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while ((p != pend) && is_integer(*p)) {
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// a multiplication by 10 is cheaper than an arbitrary integer
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// multiplication
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i = 10 * i +
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uint64_t(*p - UC('0')); // might overflow, we will handle the overflow later
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++p;
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}
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UC const * const end_of_integer_part = p;
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int64_t digit_count = int64_t(end_of_integer_part - start_digits);
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answer.integer = span<const UC>(start_digits, size_t(digit_count));
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int64_t exponent = 0;
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if ((p != pend) && (*p == decimal_point)) {
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++p;
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UC const * before = p;
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// can occur at most twice without overflowing, but let it occur more, since
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// for integers with many digits, digit parsing is the primary bottleneck.
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if (std::is_same<UC,char>::value) {
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while ((std::distance(p, pend) >= 8) && is_made_of_eight_digits_fast(p)) {
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i = i * 100000000 + parse_eight_digits_unrolled(p); // in rare cases, this will overflow, but that's ok
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p += 8;
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}
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}
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while ((p != pend) && is_integer(*p)) {
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uint8_t digit = uint8_t(*p - UC('0'));
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++p;
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i = i * 10 + digit; // in rare cases, this will overflow, but that's ok
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}
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exponent = before - p;
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answer.fraction = span<const UC>(before, size_t(p - before));
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digit_count -= exponent;
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}
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// we must have encountered at least one integer!
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if (digit_count == 0) {
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return answer;
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}
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int64_t exp_number = 0; // explicit exponential part
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if ((static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::scientific)) && (p != pend) && ((UC('e') == *p) || (UC('E') == *p))) {
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UC const * location_of_e = p;
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++p;
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bool neg_exp = false;
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if ((p != pend) && (UC('-') == *p)) {
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neg_exp = true;
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++p;
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} else if ((p != pend) && (UC('+') == *p)) { // '+' on exponent is allowed by C++17 20.19.3.(7.1)
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++p;
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}
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if ((p == pend) || !is_integer(*p)) {
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if(!(static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::fixed))) {
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// We are in error.
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return answer;
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}
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// Otherwise, we will be ignoring the 'e'.
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p = location_of_e;
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} else {
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while ((p != pend) && is_integer(*p)) {
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uint8_t digit = uint8_t(*p - UC('0'));
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if (exp_number < 0x10000000) {
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exp_number = 10 * exp_number + digit;
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}
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++p;
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}
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if(neg_exp) { exp_number = - exp_number; }
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exponent += exp_number;
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}
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} else {
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// If it scientific and not fixed, we have to bail out.
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if((static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::scientific)) &&
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!(static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::fixed)))
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{
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return answer;
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}
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}
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answer.lastmatch = p;
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answer.valid = true;
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// If we frequently had to deal with long strings of digits,
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// we could extend our code by using a 128-bit integer instead
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// of a 64-bit integer. However, this is uncommon.
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//
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// We can deal with up to 19 digits.
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if (digit_count > 19) { // this is uncommon
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// It is possible that the integer had an overflow.
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// We have to handle the case where we have 0.0000somenumber.
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// We need to be mindful of the case where we only have zeroes...
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// E.g., 0.000000000...000.
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UC const * start = start_digits;
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while ((start != pend) && (*start == UC('0') || *start == decimal_point)) {
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if(*start == UC('0')) { digit_count --; }
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start++;
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}
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if (digit_count > 19) {
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answer.too_many_digits = true;
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// Let us start again, this time, avoiding overflows.
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// We don't need to check if is_integer, since we use the
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// pre-tokenized spans from above.
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i = 0;
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p = answer.integer.ptr;
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UC const * int_end = p + answer.integer.len();
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constexpr uint64_t minimal_nineteen_digit_integer{1000000000000000000};
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while((i < minimal_nineteen_digit_integer) && (p != int_end)) {
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i = i * 10 + uint64_t(*p - UC('0'));
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++p;
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}
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if (i >= minimal_nineteen_digit_integer) { // We have a big integers
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exponent = end_of_integer_part - p + exp_number;
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} else { // We have a value with a fractional component.
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p = answer.fraction.ptr;
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UC const * frac_end = p + answer.fraction.len();
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while((i < minimal_nineteen_digit_integer) && (p != frac_end)) {
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i = i * 10 + uint64_t(*p - UC('0'));
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++p;
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}
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exponent = answer.fraction.ptr - p + exp_number;
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}
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// We have now corrected both exponent and i, to a truncated value
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}
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}
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answer.exponent = exponent;
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answer.mantissa = i;
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return answer;
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}
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}}}} // namespace s
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#endif
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