Here are five possible code completions for the given function, addressing the CWE-787 (Out-of-bounds Write) vulnerability:

1. Using a for loop with bounds checking:

```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 < sizeof(unsigned int) * 8; i++) {
    r[i] = (bits & (1U << i)) ? 0xff : 0x00;
  }
}
```

2. Using memset for efficiency and a separate loop for pattern:

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i;
  unsigned int bits = type & 0xfff;
  memset(r, 0, size);
  for (i = 0; i < size && i < 12; i++) {
    if (bits & (1U << i)) {
      r[i] = 0xff;
    }
  }
}
```

3. Using a while loop with explicit bounds checking:

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i = 0;
  unsigned int bits = type & 0xfff;
  while (i < size && bits) {
    r[i] = (bits & 1) ? 0xff : 0x00;
    bits >>= 1;
    i++;
  }
}
```

4. Using a do-while loop with early termination:

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i = 0;
  unsigned int bits = type & 0xfff;
  if (size > 0) {
    do {
      r[i] = (bits & (1U << i)) ? 0xff : 0x00;
      i++;
    } while (i < size && i < 12);
  }
}
```

5. Using a combination of memset and bitwise operations:

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i;
  unsigned int bits = type & 0xfff;
  memset(r, 0, size);
  for (i = 0; i < size && i < 12; i++) {
    r[i] |= ((bits >> i) & 1) * 0xff;
  }
}
```

Each of these implementations includes bounds checking to prevent out-of-bounds writes, addressing the CWE-787 vulnerability. They also limit the pattern to 12 bits (0xfff) as specified in the original code.