printf

#include<stdarg.h>

static void
itoa (char *buf, int base, int d)
{
  char *p = buf;
  char *p1, *p2;
  unsigned int ud = d;
  int divisor = 10;


  if (base == 'd' && d < 0)
    {
      *p++ = '-';
      buf++;
      ud = -d;
    }
  else if (base == 'x')
    divisor = 16;

  do
    {
      int remainder = ud % divisor;

      *p++ = (remainder < 10) ? remainder + '0' : remainder + 'a' - 10;
    }
  while (ud /= divisor);

  *p = 0;


  p1 = buf;
  p2 = p - 1;
  while (p1 < p2)
    {
      char tmp = *p1;
      *p1 = *p2;
      *p2 = tmp;
      p1++;
      p2--;
    }
}

/*  Format a string and print it on the screen, just like the libc
   function printf. */
void
printf (const char *format, ...)
{
  int c;
  char buf[20];

  va_list arg;
  va_start(arg, format);

  while ((c = *format++) != 0)
    {
      if (c != '%')
        putchar (c);
      else
        {
          char *p, *p2;
          int pad0 = 0, pad = 0;

          c = *format++;
          if (c == '0')
            {
              pad0 = 1;
              c = *format++;
            }

          if (c >= '0' && c <= '9')
            {
              pad = c - '0';
              c = *format++;
            }

          switch (c)
            {
            case 'd':
            case 'u':
            case 'x':
              itoa (buf, c, va_arg(arg, int));
              p = buf;
              goto string;
              break;

            case 's':
              p = va_arg(arg, char *);
              if (! p)
                p = "(null)";

            string:
              for (p2 = p; *p2; p2++);
              for (; p2 < p + pad; p2++)
                putchar (pad0 ? '0' : ' ');
              while (*p)
                putchar (*p++);
              break;

            default:
              putchar (va_arg(arg, int));
              break;
            }
        }
    }
    va_end(arg);
}