Function encodeKVFragment

fdbserver/KeyValueStoreSQLite.actor.cpp:492–542

// Note that changing the following value constitutes a change in index numbering.
#define KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR 4
Value encodeKVFragment(KeyValueRef kv, uint32_t index) {
	int keyCode = kv.key.size() * 2 + 12;
	int valCode = kv.value.size() * 2 + 12;
	// The SQLite type code for the index is the minimal number of bytes needed to store
	// a signed representation of the index value.  The type code for 0 is 0 (which is
	// actually the null type in SQLite).
	int8_t indexCode = 0;
	if (index != 0) {
		uint32_t tmp = index;
		while (tmp != 0) {
			++indexCode;
			tmp >>= 8;
		}
		// An increment is required if the high bit of the N-byte index value is set, since it is
		// positive number but SQLite only stores signed values and would interpret it as negative.
		if (index >> (8 * indexCode - 1))
			++indexCode;
	}

	int header_size = sqlite3VarintLen(keyCode) + sizeof(indexCode) + sqlite3VarintLen(valCode);
	int hh = sqlite3VarintLen(header_size);
	header_size += hh;
	if (hh < sqlite3VarintLen(header_size))
		header_size++;
	int size = header_size + kv.key.size() + indexCode + kv.value.size();

	Value v;
	uint8_t* d = new (v.arena()) uint8_t[size];
	((ValueRef&)v) = KeyRef(d, size);
	d += sqlite3PutVarint(d, header_size);
	d += sqlite3PutVarint(d, keyCode);
	*d++ = indexCode;
	d += sqlite3PutVarint(d, valCode);

	// Write key
	memcpy(d, kv.key.begin(), kv.key.size());
	d += kv.key.size();

	// Write index bytes, if any
	for (int i = indexCode - 1; i >= 0; --i) {
		d[i] = (uint8_t)index;
		index >>= 8;
	}
	d += indexCode;

	// Write value
	memcpy(d, kv.value.begin(), kv.value.size());
	d += kv.value.size();
	ASSERT(d == v.begin() + size);
	return v;
}

int getEncodedSize(int keySize, int valuePrefixSize) {
	int keyCode = keySize * 2 + 12;