libc/src/__support/str_to_integer.h

//===-- String to integer conversion utils ----------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// -----------------------------------------------------------------------------
//                               **** WARNING ****
// This file is shared with libc++. You should also be careful when adding
// dependencies to this file, since it needs to build for all libc++ targets.
// -----------------------------------------------------------------------------

#ifndef LLVM_LIBC_SRC___SUPPORT_STR_TO_INTEGER_H
#define LLVM_LIBC_SRC___SUPPORT_STR_TO_INTEGER_H

#include "hdr/errno_macros.h" // For ERANGE
#include "src/__support/CPP/limits.h"
#include "src/__support/CPP/type_traits.h"
#include "src/__support/CPP/type_traits/make_unsigned.h"
#include "src/__support/big_int.h"
#include "src/__support/common.h"
#include "src/__support/ctype_utils.h"
#include "src/__support/macros/config.h"
#include "src/__support/str_to_num_result.h"
#include "src/__support/uint128.h"
#include "src/__support/wctype_utils.h"

namespace LIBC_NAMESPACE_DECL {
namespace internal {

// Returns the idx to the first character in src that is not a whitespace
// character (as determined by isspace())
template <typename CharType>
LIBC_INLINE constexpr size_t
first_non_whitespace(const CharType *__restrict src,
                     size_t src_len = cpp::numeric_limits<size_t>::max()) {
  size_t src_cur = 0;
  for (; src_cur < src_len && internal::isspace(src[src_cur]); ++src_cur)
    ;
  return src_cur;
}

// Returns +1, -1, or 0 if 'src' starts with (respectively)
// plus sign, minus sign, or neither.
template <typename CharType>
LIBC_INLINE static int get_sign(const CharType *__restrict src) {
  if (is_char_or_wchar(src[0], '+', L'+'))
    return 1;
  if (is_char_or_wchar(src[0], '-', L'-'))
    return -1;
  return 0;
}

// checks if the next 3 characters of the string pointer are the start of a
// hexadecimal number. Does not advance the string pointer.
template <typename CharType>
LIBC_INLINE static bool is_hex_start(const CharType *__restrict src,
                                     size_t src_len) {
  if (src_len < 3)
    return false;
  return is_char_or_wchar(src[0], '0', L'0') &&
         is_char_or_wchar(tolower(src[1]), 'x', L'x') && isalnum(src[2]) &&
         b36_char_to_int(src[2]) < 16;
}

// checks if the next 3 characters of the string pointer are the start of a
// binary number. Does not advance the string pointer.
template <typename CharType>
LIBC_INLINE static bool is_binary_start(const CharType *__restrict src,
                                        size_t src_len) {
  if (src_len < 3)
    return false;
  return is_char_or_wchar(src[0], '0', L'0') &&
         is_char_or_wchar(tolower(src[1]), 'b', L'b') && isalnum(src[2]) &&
         b36_char_to_int(src[2]) < 2;
}

// Takes the address of the string pointer and parses the base from the start of
// it.
template <typename CharType>
LIBC_INLINE static int infer_base(const CharType *__restrict src,
                                  size_t src_len) {
  // A hexadecimal number is defined as "the prefix 0x or 0X followed by a
  // sequence of the decimal digits and the letters a (or A) through f (or F)
  // with values 10 through 15 respectively." (C standard 6.4.4.1)
  if (is_hex_start(src, src_len))
    return 16;
  // A binary number is defined as "the prefix 0b or 0B optionally followed
  // by a sequence of letters and digits." (C standard 7.24.1.7)
  if (is_binary_start(src, src_len))
    return 2;
  // An octal number is defined as "the prefix 0 optionally followed by a
  // sequence of the digits 0 through 7 only" (C standard 6.4.4.1) and so any
  // number that starts with 0, including just 0, is an octal number.
  if (src_len > 0 && is_char_or_wchar(src[0], '0', L'0')) {
    return 8;
  }
  // A decimal number is defined as beginning "with a nonzero digit and
  // consist[ing] of a sequence of decimal digits." (C standard 6.4.4.1)
  return 10;
}

// -----------------------------------------------------------------------------
//                               **** WARNING ****
// This interface is shared with libc++, if you change this interface you need
// to update it in both libc and libc++.
// -----------------------------------------------------------------------------
// Takes a pointer to a string and the base to convert to. This function is used
// as the backend for all of the string to int functions.
template <typename T, typename CharType>
LIBC_INLINE constexpr StrToNumResult<T>
strtointeger(const CharType *__restrict src, int base,
             const size_t src_len = cpp::numeric_limits<size_t>::max()) {
  using ResultType = make_integral_or_big_int_unsigned_t<T>;

  if (src_len == 0)
    return {0, 0, 0};

  if (base < 0 || base == 1 || base > 36)
    return {0, 0, EINVAL};

  size_t src_cur = first_non_whitespace(src, src_len);
  if (src_cur == src_len) {
    return {0, 0, 0};
  }

  int sign = get_sign(src + src_cur);
  bool is_positive = (sign >= 0);
  src_cur += (sign != 0);

  if (base == 0)
    base = infer_base(src + src_cur, src_len - src_cur);

  if (base == 16 && is_hex_start(src + src_cur, src_len - src_cur))
    src_cur = src_cur + 2;

  if (base == 2 && is_binary_start(src + src_cur, src_len - src_cur))
    src_cur = src_cur + 2;

  constexpr bool IS_UNSIGNED = cpp::is_unsigned_v<T>;
  ResultType constexpr NEGATIVE_MAX =
      !IS_UNSIGNED ? static_cast<ResultType>(cpp::numeric_limits<T>::max()) + 1
                   : cpp::numeric_limits<T>::max();
  ResultType const abs_max =
      (is_positive ? cpp::numeric_limits<T>::max() : NEGATIVE_MAX);
  ResultType const abs_max_div_by_base =
      abs_max / static_cast<ResultType>(base);

  bool is_number = false;
  int error_val = 0;
  ResultType result = 0;
  while (src_cur < src_len && isalnum(src[src_cur])) {
    int cur_digit = b36_char_to_int(src[src_cur]);
    if (cur_digit >= base)
      break;

    is_number = true;
    ++src_cur;

    // If the number has already hit the maximum value for the current type then
    // the result cannot change, but we still need to advance src to the end of
    // the number.
    if (result == abs_max) {
      error_val = ERANGE;
      continue;
    }

    if (result > abs_max_div_by_base) {
      result = abs_max;
      error_val = ERANGE;
    } else {
      result = result * static_cast<ResultType>(base);
    }
    if (result > abs_max - static_cast<ResultType>(cur_digit)) {
      result = abs_max;
      error_val = ERANGE;
    } else {
      result = result + static_cast<ResultType>(cur_digit);
    }
  }

  ptrdiff_t str_len = is_number ? static_cast<ptrdiff_t>(src_cur) : 0;

  if (error_val == ERANGE) {
    if (is_positive || IS_UNSIGNED)
      return {cpp::numeric_limits<T>::max(), str_len, error_val};
    else // T is signed and there is a negative overflow
      return {cpp::numeric_limits<T>::min(), str_len, error_val};
  }

  return {static_cast<T>(is_positive ? result : -result), str_len, error_val};
}

} // namespace internal
} // namespace LIBC_NAMESPACE_DECL

#endif // LLVM_LIBC_SRC___SUPPORT_STR_TO_INTEGER_H