#include <ctype.h>

float strtof(const char *str, char **endptr)
{
    float res = 0.0F;
    char *ptr = (char*)str;
    int after_dot = 0;
    float div = 1;

    while (*ptr != '\0') {
        if (isdigit(*ptr)) {
            if (!after_dot) {
                res *= 10;
                res += *ptr - '0';
            } else {
                div *= 10;
                res += (float)(*ptr - '0') / div;
            }
        } else if (*ptr == '.') {
            after_dot = 1;
        } else {
            break;
        }

        ptr++;
    }

    if (endptr) {
        *endptr = ptr;
    }

    return res;
}