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https://github.com/fastfloat/fast_float.git
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247 lines
7.6 KiB
C++
247 lines
7.6 KiB
C++
#ifndef FASTFLOAT_ASCII_NUMBER_H
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#define FASTFLOAT_ASCII_NUMBER_H
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#include <cstdio>
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#include <cctype>
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#include <cstdint>
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#include <cstring>
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#include "float_common.h"
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namespace fast_float {
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fastfloat_really_inline bool is_integer(char c) noexcept { return (c & 0x30) == 0x30; }
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// credit: https://johnnylee-sde.github.io/Fast-numeric-string-to-int/
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fastfloat_really_inline uint32_t parse_eight_digits_unrolled(const char *chars) noexcept {
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uint64_t val;
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::memcpy(&val, chars, sizeof(uint64_t));
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val = (val & 0x0F0F0F0F0F0F0F0F) * 2561 >> 8;
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val = (val & 0x00FF00FF00FF00FF) * 6553601 >> 16;
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return uint32_t((val & 0x0000FFFF0000FFFF) * 42949672960001 >> 32);
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}
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fastfloat_really_inline bool is_made_of_eight_digits_fast(uint64_t val) noexcept {
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return (((val & 0xF0F0F0F0F0F0F0F0) |
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(((val + 0x0606060606060606) & 0xF0F0F0F0F0F0F0F0) >> 4)) ==
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0x3333333333333333);
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}
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fastfloat_really_inline bool is_made_of_eight_digits_fast(const char *chars) noexcept {
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uint64_t val;
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::memcpy(&val, chars, 8);
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return is_made_of_eight_digits_fast(val);
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}
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struct parsed_number_string {
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int64_t exponent;
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uint64_t mantissa;
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const char *lastmatch;
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bool negative;
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bool valid;
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bool too_many_digits;
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};
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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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fastfloat_really_inline
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parsed_number_string parse_number_string(const char *p, const char *pend, chars_format fmt) noexcept {
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parsed_number_string answer;
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answer.valid = false;
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answer.negative = (*p == '-');
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if ((*p == '-') || (*p == '+')) {
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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 != '.')) { // 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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const char *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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(*p - '0'); // might overflow, we will handle the overflow later
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++p;
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}
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int64_t exponent = 0;
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if ((p != pend) && (*p == '.')) {
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++p;
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const char *first_after_period = p;
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if ((p + 8 <= pend) && 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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if ((p + 8 <= pend) && 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 - '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 = first_after_period - p;
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}
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// we must have encountered at least one integer!
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if ((start_digits == p) || ((start_digits == p - 1) && (*start_digits == '.') )) {
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return answer;
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}
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int32_t digit_count =
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int32_t(p - start_digits - 1); // used later to guard against overflows
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if ((fmt & chars_format::scientific) && (p != pend) && (('e' == *p) || ('E' == *p))) {
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const char * location_of_e = p;
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int64_t exp_number = 0; // exponential part
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++p;
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bool neg_exp = false;
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if ((p != pend) && ('-' == *p)) {
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neg_exp = true;
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++p;
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} else if ((p != pend) && ('+' == *p)) {
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++p;
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}
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if ((p == pend) || !is_integer(*p)) {
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if(!(fmt & 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 - '0');
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if (exp_number < 0x10000) {
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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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exponent += (neg_exp ? -exp_number : 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((fmt & chars_format::scientific) && !(fmt & chars_format::fixed)) { return answer; }
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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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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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const char *start = start_digits;
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while (*start == '0' || (*start == '.')) {
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start++;
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}
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// we over-decrement by one when there is a decimal separator
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digit_count -= int(start - start_digits);
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if (digit_count >= 19) {
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answer.mantissa = 0xFFFFFFFFFFFFFFFF; // important: we don't want the mantissa to be used in a fast path uninitialized.
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answer.too_many_digits = true;
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return answer;
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}
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}
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answer.too_many_digits = false;
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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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// This should always succeed since it follows a call to parse_number_string
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// This function could be optimized. In particular, we could stop after 19 digits
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// and try to bail out. Furthermore, we should be able to recover the computed
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// exponent from the pass in parse_number_string.
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fastfloat_really_inline decimal parse_decimal(const char *p, const char *pend) noexcept {
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decimal answer;
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answer.num_digits = 0;
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answer.decimal_point = 0;
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answer.truncated = false;
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// any whitespace has been skipped.
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answer.negative = (*p == '-');
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if ((*p == '-') || (*p == '+')) {
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++p;
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}
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// skip leading zeroes
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while ((p != pend) && (*p == '0')) {
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++p;
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}
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while ((p != pend) && is_integer(*p)) {
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if (answer.num_digits < max_digits) {
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answer.digits[answer.num_digits] = uint8_t(*p - '0');
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}
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answer.num_digits++;
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++p;
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}
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if ((p != pend) && (*p == '.')) {
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++p;
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const char *first_after_period = p;
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// if we have not yet encountered a zero, we have to skip it as well
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if(answer.num_digits == 0) {
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// skip zeros
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while ((p != pend) && (*p == '0')) {
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++p;
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}
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}
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// We expect that this loop will often take the bulk of the running time
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// because when a value has lots of digits, these digits often
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while ((p + 8 <= pend) && (answer.num_digits + 8 < max_digits)) {
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uint64_t val;
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::memcpy(&val, p, sizeof(uint64_t));
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if(! is_made_of_eight_digits_fast(val)) { break; }
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// We have eight digits, process them in one go!
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val -= 0x3030303030303030;
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::memcpy(answer.digits + answer.num_digits, &val, sizeof(uint64_t));
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answer.num_digits += 8;
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p += 8;
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}
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while ((p != pend) && is_integer(*p)) {
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if (answer.num_digits < max_digits) {
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answer.digits[answer.num_digits] = uint8_t(*p - '0');
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}
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answer.num_digits++;
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++p;
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}
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answer.decimal_point = int32_t(first_after_period - p);
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}
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if ((p != pend) && (('e' == *p) || ('E' == *p))) {
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++p;
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bool neg_exp = false;
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if ((p != pend) && ('-' == *p)) {
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neg_exp = true;
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++p;
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} else if ((p != pend) && ('+' == *p)) {
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++p;
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}
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int32_t exp_number = 0; // exponential part
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while ((p != pend) && is_integer(*p)) {
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uint8_t digit = uint8_t(*p - '0');
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if (exp_number < 0x10000) {
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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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answer.decimal_point += (neg_exp ? -exp_number : exp_number);
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}
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answer.decimal_point += answer.num_digits;
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if(answer.num_digits > max_digits) {
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answer.truncated = true;
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answer.num_digits = max_digits;
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}
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return answer;
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}
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} // namespace fast_float
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#endif
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