strtol zanim sie zjebie

#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <limits.h>


long strtol(char* nptr, char **endptr , int base)
{
    char *string;  //points at the character being currently converted
    long returnedNumber = 0;
    int numberOutsideTheLimit = 0;
    int sign;
    int addedDigit;


    assert(nptr); // quits if (nptr = NULL)
    string = nptr;

    while(isspace(*string))
    {
        string++;
    }

    if(*string =='-')
    {
        sign = 1;
        string++;
    }
    else
    {
        if(*string =='+')
        {
            sign = 0;
            string++;
        }
        else
        {
            sign = 0;
        }
    }

    if((base == 8) && (*string =='0'))
    {
        string++;
    }

    if((base == 16) && (*string == '0'))
    {
        string++;

        if((*string =='x')||(*string =='X'))
        {
            string++;
        }
        else
        {
            string--;
        }
    }
    if((*string =='0') && (base == 0))
    {
        base = 8;
        string++;

        if((*string =='x')||(*string =='X'))
        {
            base = 16;
            string++;
        }

    }
    else if(base == 0) //if the base is 0 and the beginning of string is not 0, 0x or 0X then the base is 10
    {
        base = 10;
    }

    if(base < 2 || base > 36)
    {
        errno = EINVAL;
        return 0;
    }

    if((base == 8) && ((*string < '0')||(*string >'7')))
    {
        *endptr = string;
        return 0;
    }

    if((base == 16) && ((*string < '0') || ((*string > '9')&&(*string < 'A')) || ((*string > 'F') && (*string < 'a')) || (*string >'f')))
    {
        string--;
        *endptr = string;
        return 0;
    }

    while(*string!='\0') /* This loop terminates when string points to the end of the file*/
    {
        if (isdigit(*string))/* if string does not point to a digit isdigit returns 0, otherwise it returns this digit*/
        {
            addedDigit = *string - '0'; /*converting ASCII code to corresponding digit*/
        }
        else
        {
            if(isalpha(*string)) /* isalpha returns 0 if string does not point to a letter, otherwise it returns that letter */
            {
                if(islower(*string)) /* checks if the string points to the lower case letter */
                {
                    addedDigit = (*string - 'a') + 10; /* converts lower case letters in ASCII code to corresponding digits in numerical systems */
                }
                else
                    addedDigit = (*string - 'A') + 10; /* converts upper case letters in ASCII code to corresponding digits in numerical systems */
            }
            else /* loop is terminated if string does not point to digits or letters */
            {
                break;
            }
        }
        switch(sign)
        {
        case 0:
        {
            if (numberOutsideTheLimit < 0 || returnedNumber > ((LONG_MAX-addedDigit)/base) /*|| (number == limit && (int) digit > limit_mod)*/)
            {/* checks if the number is inside the limits for long int, if not numberOutsideTheLimit=-1 and the string proceedes to the end of the file */
                numberOutsideTheLimit =-1;
                string++;
            }
            else /* if the number is inside the limits then numberOutsideTheLimit=1 and current digit is attached to the number */
            {
                numberOutsideTheLimit = 1;
                returnedNumber = (returnedNumber*base)+addedDigit;
                string++;
            }
            break;

        }
        case 1:
        {
            if (numberOutsideTheLimit < 0 || returnedNumber < ((LONG_MIN+addedDigit)/base))
            {/* checks if the number is inside the limits for long int, if not numberOutsideTheLimit=-1 and the string proceedes to the end of the file */
                numberOutsideTheLimit =-1;
                string++;
            }
            else /* if the number is inside the limits then numberOutsideTheLimit=1 and current digit is attached to the number */
            {
                numberOutsideTheLimit = 1;
                returnedNumber = (returnedNumber*base)-addedDigit;
                string++;
            }

            break;
        }
        }
    }
    if (numberOutsideTheLimit<0)/* if numberOutsideTheLimit=-1 then the number is outside limits so function will return LONG_MIN or LONG_MAX depending on sign */
            {
                returnedNumber = sign ? LONG_MIN : LONG_MAX;
                errno = ERANGE;
            }

    if (endptr != '\0') /* if endpointer is something other than NULL then for numberOutsideTheLimit=1 (number inside limits) it points to string (current character) and for numberOutsideTheLimit=-1 (number outside limits) it points to nptr (the whole string) */
        *endptr = numberOutsideTheLimit ? string : (char *) nptr;

return returnedNumber;
}