RossComputerGuy/stardustos

/**
    * StardustOS libc - (C) 2019 Tristan Ross
    */
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static char* convert(unsigned int num, int base) {
    static char* rep = "0123456789ABCDEF";
    static char buff[50];
    char* ptr = &buff[49];
    *ptr = '\0';
    do {
        *--ptr = rep[num % base];
        num /= base;
    } while (num != 0);
    return ptr;
}

int vsnprintf(char* str, size_t size, const char* format, va_list ap) {
    int wrote = 0;
    char* traverse = (char*)format;
    int i = 0;
    unsigned int si = 0;
    char* s = NULL;
    for (; *traverse != 0; traverse++) {
        while (*traverse != '%' && *traverse != 0) {
            if (wrote < size) str[wrote] = *traverse;
            wrote++;
            traverse++;
        }
        if (*traverse == 0) break;
        traverse++;
        switch (*traverse) {
            case 'c':
                i = va_arg(ap, int);
                if (wrote < size) str[wrote] = *traverse;
                wrote++;
                break;
            case 'd':
                i = va_arg(ap, int);
                if (i < 0) {
                    i = -i;
                    if (wrote < size) str[wrote] = '-';
                    wrote++;
                }
                s = convert(i, 10);
                if (wrote < size) strncpy((char*)(str + wrote), s, strlen(s));
                wrote += strlen(s);
                break;
            case 'o':
                si = va_arg(ap, unsigned int);
                s = convert(si, 10);
                if (wrote < size) strncpy((char*)(str + wrote), s, strlen(s));
                wrote += strlen(s);
                break;
            case 's':
                s = va_arg(ap, char*);
                if (s == NULL) s = "(null)";
                if (wrote < size) strncpy((char*)(str + wrote), s, strlen(s));
                wrote += strlen(s);
                break;
            case 'x':
                si = va_arg(ap, unsigned int);
                s = convert(si, 10);
                if (wrote < size) strncpy((char*)(str + wrote), s, strlen(s));
                wrote += strlen(s);
                break;
            case 'f':
                {
                    double v = va_arg(ap, double);
                    static char temp[50];
                    i = ftoa(v, temp);
                    if (wrote < size) strncpy((char*)(str + wrote), temp, i);
                    wrote += i;
                }
                break;
            case 'l':
                if (traverse[1] == 'u') {
                    unsigned long lu = va_arg(ap, unsigned long);
                    s = convert(lu, 10);
                } else {
                    long l = va_arg(ap, long);
                    s = convert(l, 10);
                }
                if (wrote < size) strncpy((char*)(str + wrote), s, strlen(s));
                wrote += strlen(s);
                break;
            case '%':
                if (wrote < size) str[wrote] = '%';
                wrote++;
                break;
        }
    }
    str[wrote] = 0;
    return wrote - 1;
}