int2str.cc

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#include <assert.h>
#include <stdint.h>
#include <string.h>
#include <iterator>

#include "integer_digits.h"
#include "m_string.h"  // IWYU pragma: keep

/*
  _dig_vec arrays are public because they are used in several outer places.
*/
const char _dig_vec_upper[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const char _dig_vec_lower[] = "0123456789abcdefghijklmnopqrstuvwxyz";

/**
  Converts a 64-bit integer value to its character form and moves it to the
  destination buffer followed by a terminating NUL. If radix is -2..-36, val is
  taken to be SIGNED, if radix is 2..36, val is taken to be UNSIGNED. That is,
  val is signed if and only if radix is. All other radixes are treated as bad
  and nothing will be changed in this case.

  For conversion to decimal representation (radix is -10 or 10) one should use
  the optimized #longlong10_to_str() function instead.

  @param val the value to convert
  @param dst the buffer where the string representation should be stored
  @param radix radix of scale of notation
  @param upcase true if we should use upper-case digits

  @return pointer to the ending NUL character, or nullptr if radix is bad
*/
char *ll2str(int64_t val, char *dst, int radix, bool upcase) {
  char buffer[65];
  const char *const dig_vec = upcase ? _dig_vec_upper : _dig_vec_lower;
  auto uval = static_cast<uint64_t>(val);

  if (radix < 0) {
    if (radix < -36 || radix > -2) return nullptr;
    if (val < 0) {
      *dst++ = '-';
      /* Avoid integer overflow in (-val) for LLONG_MIN (BUG#31799). */
      uval = 0ULL - uval;
    }
    radix = -radix;
  } else if (radix > 36 || radix < 2) {
    return nullptr;
  }

  char *p = std::end(buffer);
  do {
    *--p = dig_vec[uval % radix];
    uval /= radix;
  } while (uval != 0);

  const size_t length = std::end(buffer) - p;
  memcpy(dst, p, length);
  dst[length] = '\0';
  return dst + length;
}

/**
  Converts a 64-bit integer to its string representation in decimal notation.

  It is optimized for the normal case of radix 10/-10. It takes only the sign of
  radix parameter into account and not its absolute value.

  @param val the value to convert
  @param dst the buffer where the string representation should be stored
  @param radix 10 if val is unsigned, -10 if val is signed

  @return pointer to the ending NUL character
*/
char *longlong10_to_str(int64_t val, char *dst, int radix) {
  assert(radix == 10 || radix == -10);

  uint64_t uval = static_cast<uint64_t>(val);

  if (radix < 0) /* -10 */
  {
    if (val < 0) {
      *dst++ = '-';
      /* Avoid integer overflow in (-val) for LLONG_MIN (BUG#31799). */
      uval = uint64_t{0} - uval;
    }
  }

  char *end = write_digits(uval, count_digits(uval), dst);
  *end = '\0';
  return end;
}