Here are five possible code completions for the given function:

**1. Fill with a repeating pattern of bits**

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i;
  unsigned int bits = type & 0xfff;
  for (i = 0; i < size; i++) {
    r[i] = (unsigned char)(bits >> (i % 12));
  }
}
```

**2. Fill with a repeating pattern of bytes**

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i;
  unsigned int bits = type & 0xfff;
  unsigned char pattern = (unsigned char)bits;
  for (i = 0; i < size; i++) {
    r[i] = pattern;
  }
}
```

**3. Fill with a random pattern based on the type**

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i;
  unsigned int bits = type & 0xfff;
  srand(bits); // seed the random number generator
  for (i = 0; i < size; i++) {
    r[i] = (unsigned char)(rand() % 256);
  }
}
```

**4. Fill with a pattern of increasing bytes**

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i;
  unsigned int bits = type & 0xfff;
  unsigned char start = (unsigned char)bits;
  for (i = 0; i < size; i++) {
    r[i] = start + (unsigned char)i;
  }
}
```

**5. Fill with a pattern of alternating bytes**

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i;
  unsigned int bits = type & 0xfff;
  unsigned char pattern1 = (unsigned char)bits;
  unsigned char pattern2 = (unsigned char)~bits;
  for (i = 0; i < size; i++) {
    r[i] = (i % 2 == 0) ? pattern1 : pattern2;
  }
}
```

Note that the actual implementation will depend on the specific requirements of the `fillpattern` function.