dep: Add fast_float

dep/fast_float/include/fast_float/ascii_number.h

@@ -0,0 +1,227 @@
+#ifndef FASTFLOAT_ASCII_NUMBER_H
+#define FASTFLOAT_ASCII_NUMBER_H
+
+#include <cctype>
+#include <cstdint>
+#include <cstring>
+#include <iterator>
+
+#include "float_common.h"
+
+namespace fast_float {
+
+// Next function can be micro-optimized, but compilers are entirely
+// able to optimize it well.
+fastfloat_really_inline bool is_integer(char c)  noexcept  { return c >= '0' && c <= '9'; }
+
+fastfloat_really_inline 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;
+}
+
+fastfloat_really_inline uint64_t read_u64(const char *chars) {
+  uint64_t val;
+  ::memcpy(&val, chars, sizeof(uint64_t));
+#if FASTFLOAT_IS_BIG_ENDIAN == 1
+  // Need to read as-if the number was in little-endian order.
+  val = byteswap(val);
+#endif
+  return val;
+}
+
+fastfloat_really_inline void write_u64(uint8_t *chars, uint64_t val) {
+#if 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
+fastfloat_really_inline uint32_t  parse_eight_digits_unrolled(uint64_t val) {
+  const uint64_t mask = 0x000000FF000000FF;
+  const uint64_t mul1 = 0x000F424000000064; // 100 + (1000000ULL << 32)
+  const 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);
+}
+
+fastfloat_really_inline uint32_t parse_eight_digits_unrolled(const char *chars)  noexcept  {
+  return parse_eight_digits_unrolled(read_u64(chars));
+}
+
+// credit @aqrit
+fastfloat_really_inline bool is_made_of_eight_digits_fast(uint64_t val)  noexcept  {
+  return !((((val + 0x4646464646464646) | (val - 0x3030303030303030)) &
+     0x8080808080808080));
+}
+
+fastfloat_really_inline bool is_made_of_eight_digits_fast(const char *chars)  noexcept  {
+  return is_made_of_eight_digits_fast(read_u64(chars));
+}
+
+typedef span<const char> byte_span;
+
+struct parsed_number_string {
+  int64_t exponent{0};
+  uint64_t mantissa{0};
+  const char *lastmatch{nullptr};
+  bool negative{false};
+  bool valid{false};
+  bool too_many_digits{false};
+  // contains the range of the significant digits
+  byte_span integer{};  // non-nullable
+  byte_span fraction{}; // nullable
+};
+
+// Assuming that you use no more than 19 digits, this will
+// parse an ASCII string.
+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 ((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;
+}
+
+} // namespace fast_float
+
+#endif