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#include <cstdint>
#include <limits>
namespace OpenVic::StringUtils {
/* The constexpr function 'string_to_int64' will convert a string into a int64 integer value.
* The function takes four parameters: the input string (as a pair of pointers marking the start and
* end of the string), a bool pointer for reporting success, and the base for numerical conversion.
* The base parameter defaults to 10 (decimal), but it can be any value between 2 and 36. If the base
* given is 0, it will be set to 16 if the string starts with "0x" or "0X", otherwise 8 if the string
* still starts with "0", otherwise 10. The success bool pointer parameter is used to report whether
* or not conversion was successful. It can be nullptr if this information is not needed.
*/
constexpr int64_t string_to_int64(char const* str, const char* end, bool* successful, int base = 10) {
if (successful != nullptr) *successful = false;
// Base value should be between 2 and 36. If it's not, return 0 as an invalid case.
if (str == nullptr || end <= str || base < 0 || base == 1 || base > 36)
return 0;
// The result of the conversion will be stored in this variable.
int64_t result = 0;
// This flag will be set if the number is negative.
bool is_negative = false;
// Check if there is a sign character.
if (*str == '+' || *str == '-') {
if (*str == '-')
is_negative = true;
++str;
if (str == end) return 0;
}
// If base is zero, base is determined by the string prefix.
if (base == 0) {
if (*str == '0') {
if (str + 1 != end && (str[1] == 'x' || str[1] == 'X')) {
base = 16; // Hexadecimal.
str += 2; // Skip '0x' or '0X'
if (str == end) return 0;
} else {
base = 8; // Octal.
}
} else {
base = 10; // Decimal.
}
} else if (base == 16) {
// If base is 16 and string starts with '0x' or '0X', skip these characters.
if (*str == '0' && str + 1 != end && (str[1] == 'x' || str[1] == 'X')) {
str += 2;
if (str == end) return 0;
}
}
// Convert the number in the string.
for (; str != end; ++str) {
int digit;
if (*str >= '0' && *str <= '9') {
digit = *str - '0'; // Calculate digit value for '0'-'9'.
} else if (*str >= 'a' && *str <= 'z') {
digit = *str - 'a' + 10; // Calculate digit value for 'a'-'z'.
} else if (*str >= 'A' && *str <= 'Z') {
digit = *str - 'A' + 10; // Calculate digit value for 'A'-'Z'.
} else {
break; // Stop conversion if current character is not a digit.
}
if (digit >= base) {
break; // Stop conversion if current digit is greater than or equal to the base.
}
// Check for overflow on multiplication
if (result > std::numeric_limits<int64_t>::max() / base) {
return is_negative ? std::numeric_limits<int64_t>::min() : std::numeric_limits<int64_t>::max();
}
result *= base;
// Check for overflow on addition
if (result > std::numeric_limits<int64_t>::max() - digit) {
return is_negative ? std::numeric_limits<int64_t>::min() : std::numeric_limits<int64_t>::max();
}
result += digit;
}
// If successful is not null and the entire string was parsed,
// set *successful to true (if not it is already false).
if (successful != nullptr && str == end) *successful = true;
// Return the result. If the number was negative, the result is negated.
return is_negative ? -result : result;
}
}
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