// Compute compressed boolean buffer
private byte[] bufB(int bpv) {
assert bpv == 1 || bpv == 2 : "Only bit vectors with/without NA are supported";
final int off = CBSChunk.OFF;
int clen = off + CBSChunk.clen(_len2, bpv);
byte bs[] = new byte[clen];
// Save the gap = number of unfilled bits and bpv value
bs[0] = (byte) (((_len2 * bpv) & 7) == 0 ? 0 : (8 - ((_len2 * bpv) & 7)));
bs[1] = (byte) bpv;
if (_len2 != _len) { // Sparse bitvector?
assert bpv == 1; // No NAs
for (int i = 0; i < _len; i++) {
int row = _xs[i];
bs[(row >> 3) + off] = CBSChunk.write1b(bs[(row >> 3) + off], (byte) 1, row & 7);
}
return bs;
}
// Dense bitvector
int boff = 0;
byte b = 0;
int idx = CBSChunk.OFF;
for (int i = 0; i < _len; i++) {
if (bpv == 1) {
assert !isNA(i);
b = CBSChunk.write1b(b, (byte) _ls[i], boff);
} else {
byte val = isNA(i) ? CBSChunk._NA : (byte) _ls[i];
b = CBSChunk.write2b(b, val, boff);
}
boff += bpv;
if (boff > 8 - bpv) {
bs[idx] = b;
boff = 0;
b = 0;
idx++;
}
}
assert bs[0] == (byte) (boff == 0 ? 0 : 8 - boff);
// Flush last byte
if (boff > 0) bs[idx++] = b;
return bs;
}