/*
 * libc.c
 *
 *  Created on: Oct 11, 2018
 *      Author: rick
 */

#include <stdlib.h>
#include <limits.h>
#include <errno.h>

/* everything of stdlib is implemented in this file except for:
 * - qsort
 **/


int abs(int val) {
    return val >= 0 ? val : (val * -1);
}

long labs(long val) {
    return val >= 0 ? val : (val * -1);
}

long long llabs(long long val) {
    return val >= 0 ? val : (val * -1);
}

// next stolen form https://www.techiedelight.com/implement-itoa-function-in-c/
// inline function to swapc two numbers
void swapc(char *x, char *y) {
    char t = *x;
    *x = *y;
    *y = t;
}

// function to reverse buffer[i..j]
char *reverse(char *buffer, int i, int j) {
    while (i < j)
        swapc(&buffer[i++], &buffer[j--]);

    return buffer;
}

// Iterative function to implement itoa() function in C
char *itoa(int value, char *buffer, int base) {
    // invalid input
    if (base < 2 || base > 32)
        return buffer;

    // consider absolute value of number
    int n = abs(value);

    int i = 0;
    while (n) {
        int r = n % base;

        if (r >= 10)
            buffer[i++] = 65 + (r - 10);
        else
            buffer[i++] = 48 + r;

        n = n / base;
    }

    // if number is 0
    if (i == 0)
        buffer[i++] = '0';

    // If base is 10 and value is negative, the resulting string
    // is preceded with a minus sign (-)
    // With any other base, value is always considered unsigned
    if (value < 0 && base == 10)
        buffer[i++] = '-';

    buffer[i] = '\0'; // null terminate string

    // reverse the string and return it
    return reverse(buffer, 0, i - 1);
}

long strtol(const char *nptr, char **endptr, int base) {
    if (base > 36) {
        errno = EINVAL;
        return -1;
    }
    char sign = '+';
    long n = 0;
    long i;
    const char *c = nptr;
    while (*c == ' ') {
        c++;
    }
    if (*c == '+') {
        c++;
    } else if (*c == '-') {
        sign = '-';
        c++;
    }
    while (*c != '\0') {
        n *= base;
        if (*c >= '0' && *c <= '9') {
            i = *c - '0';
        } else if (*c >= 'a' && *c <= 'z') {
            i = *c - 'a' + 10;
        } else if (*c >= 'A' && *c <= 'Z') {
            i = *c - 'A' + 10;
        } else {
            errno = EINVAL;
            n = -1;
            goto _set_endptr;
        }
        if (i >= base) {
            errno = EINVAL;
            n = -1;
            goto _set_endptr;
        }
        if (i > (LONG_MAX - n)) {
            errno = ERANGE;
            n = sign == '-' ? LONG_MIN : LONG_MAX;
            goto _set_endptr;
        }
        n += i;
        c++;
    }
    if (sign == '-') {
        n *= -1;
    }
    _set_endptr:
    if (endptr != NULL) {
        *endptr = c;
    }
    return n;
}