[GitHub] [ignite-3] korlov42 commented on a diff in pull request #988: IGNITE-17400 Basic C++ binary tuple support

[GitBox <gi...@apache.org>]

korlov42 commented on code in PR #988:
URL: https://github.com/apache/ignite-3/pull/988#discussion_r941475701


##########
modules/platforms/cpp/schema/BinaryTupleParser.cpp:
##########
@@ -0,0 +1,203 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "BinaryTupleParser.h"
+
+#include <cassert>
+#include <cstring>
+#include <stdexcept>
+
+namespace {
+
+template <typename T>
+T as(ignite::BytesView bytes) noexcept {
+    T value;
+    std::memcpy(&value, bytes.data(), sizeof(T));
+    return value;
+}
+
+} // namespace
+
+namespace ignite {
+
+BinaryTupleParser::BinaryTupleParser(IntT numElements, BytesView data)
+    : binaryTuple(data)
+    , elementCount(numElements)
+    , elementIndex(0)
+    , hasNullmap(false) {
+
+    BinaryTupleHeader header;
+    header.flags = binaryTuple[0];
+
+    entrySize = header.getVarLenEntrySize();
+    hasNullmap = header.getNullMapFlag();
+
+    size_t nullmapSize = 0;
+    if (hasNullmap) {
+        nullmapSize = BinaryTupleSchema::getNullMapSize(elementCount);
+    }
+
+    size_t tableSize = entrySize * elementCount;
+    nextEntry = binaryTuple.data() + BinaryTupleHeader::SIZE + nullmapSize;
+    valueBase = nextEntry + tableSize;
+
+    nextValue = valueBase;
+
+    // Fix tuple size if needed.
+    uint64_t offset = 0;
+    static_assert(BYTE_ORDER == LITTLE_ENDIAN);
+    memcpy(&offset, nextEntry + tableSize - entrySize, entrySize);
+    const std::byte *tupleEnd = valueBase + offset;
+    if (binaryTuple.end() > tupleEnd) {
+        binaryTuple.remove_suffix(binaryTuple.end() - tupleEnd);
+    }
+}
+
+ElementView BinaryTupleParser::getNext() {
+    assert(numParsedElements() < numElements());
+
+    ++elementIndex;
+
+    uint64_t offset = 0;
+    static_assert(BYTE_ORDER == LITTLE_ENDIAN);
+    memcpy(&offset, nextEntry, entrySize);
+    nextEntry += entrySize;
+
+    const std::byte *value = nextValue;
+    nextValue = valueBase + offset;
+
+    const size_t length = nextValue - value;
+    if (length == 0 && hasNullmap && BinaryTupleSchema::hasNull(binaryTuple, elementIndex - 1)) {
+        return {};
+    }
+
+    return BytesView(value, length);
+}
+
+TupleView BinaryTupleParser::parse(IntT num) {
+    assert(elementIndex == 0);
+
+    if (num == NO_NUM) {
+        num = numElements();
+    }
+
+    TupleView tuple;
+    tuple.reserve(num);
+    while (elementIndex < num) {
+        tuple.emplace_back(getNext());
+    }
+
+    return tuple;
+}
+
+KeyView BinaryTupleParser::parseKey(IntT num) {

Review Comment:
   Why do we need this? I consider BinaryTuple as a representation of a very abstract tuple in a binary from.



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