CIS-kernel/kernel/klibc/printf.c

#include <stdarg.h>
#include <kstdint.h>
#include <khal.h>

static char *itoa(uint64_t value, char *buf, uint8_t base) {
    char *ptr = buf;
    uint64_t temp = value;
    do {
        uint64_t digit = temp % base;
        if (digit < 10)
            *ptr = '0' + digit;
        else
            *ptr = 'A' + (digit - 10);
        ptr++;
        temp /= base;
    } while (temp);
    *ptr = '\0';
    // Reverse the string
    char *start = buf;
    char *end = ptr - 1;
    while (start < end) {
        char tmp = *start;
        *start = *end;
        *end = tmp;
        start++;
        end--;
    }
    return buf;
}

void serial_printf(const char *fmt, ...) {
    char buf[32];
    va_list args;
    va_start(args, fmt);
    while (*fmt) {
        if (*fmt == '%') {
            fmt++;
            switch (*fmt) {
                case 's':
                    {
                        char *str = va_arg(args, char *);
                        while (*str)
                            serial_write_byte(*str++);
                    }
                    break;
                case 'd':
                    {
                        int64_t num = va_arg(args, int64_t);
                        itoa(num, buf, 10);
                        serial_printf("%s", buf);
                    }
                    break;
                case 'u':
                    {
                        uint64_t num = va_arg(args, uint64_t);
                        itoa(num, buf, 10);
                        serial_printf("%s", buf);
                    }
                    break;
                case 'x':
                    {
                        uint64_t num = va_arg(args, uint64_t);
                        itoa(num, buf, 16);
                        serial_printf("%s", buf);
                    }
                    break;
                case 'c':
                    serial_write_byte(va_arg(args, int));
                    break;
                default:
                    serial_write_byte(*fmt);
                    break;
            }
            fmt++;
        } else {
            serial_write_byte(*fmt++);
        }
    }
    va_end(args);
}