Introduce utility class for encoding

velox/common/encode/EncoderUtils.h

@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed 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.
+ */
+#pragma once
+
+#include <exception>
+#include <map>
+#include <string>
+
+#include <folly/Range.h>
+
+namespace facebook::velox::encoding {
+
+class EncoderException : public std::exception {
+ public:
+  explicit EncoderException(const char* msg) : msg_(msg) {}
+  const char* what() const noexcept override {
+    return msg_;
+  }
+
+ protected:
+  const char* msg_;
+};
+
+using Charset = std::array<char, 64>;
+using ReverseIndex = std::array<uint8_t, 256>;
+
+// Padding character used in encoding
+constexpr static char kPadding = '=';
+
+// Checks is there padding in encoded data
+inline bool isPadded(const char* data, size_t len) {
+  return (len > 0 && data[len - 1] == kPadding) ? true : false;
+}
+
+// Counts the number of padding characters in encoded data.
+inline size_t countPadding(const char* src, size_t len) {
+  size_t padding_count = 0;
+  while (len > 0 && src[len - 1] == kPadding) {
+    padding_count++;
+    len--;
+  }
+
+  return padding_count;
+}
+
+// Gets value corresponding to an encoded character
+inline uint8_t
+baseReverseLookup(int base, char p, const ReverseIndex& reverse_lookup) {
+  auto curr = reverse_lookup[(uint8_t)p];
+  // Value of encoded character shall be less than base.
+  if (curr >= base) {
+    throw EncoderException(
+        "decode() - invalid input string: invalid characters");
+  }
+
+  return curr;
+}
+
+//  Validate the character in charset with ReverseIndex table
+constexpr bool checkForwardIndex(
+    uint8_t idx,
+    const Charset& charset,
+    const ReverseIndex& table) {
+  return (table[static_cast<uint8_t>(charset[idx])] == idx) &&
+      (idx > 0 ? checkForwardIndex(idx - 1, charset, table) : true);
+}
+
+/// Similar to strchr(), but for null-terminated const strings.
+/// Another difference is that we do not consider "\0" to be present in the
+/// string.
+/// Returns true if "str" contains the character c.
+constexpr bool findCharacterInCharSet(
+    const Charset& charset,
+    int base,
+    uint8_t idx,
+    const char c) {
+  return idx < base &&
+      ((charset[idx] == c) ||
+       findCharacterInCharSet(charset, base, idx + 1, c));
+}
+
+//  Validate the value in ReverseIndex table with charset.
+constexpr bool checkReverseIndex(
+    uint8_t idx,
+    const Charset& charset,
+    int base,
+    const ReverseIndex& table) {
+  return (table[idx] == 255 ? !findCharacterInCharSet(
+                                  charset, base, 0, static_cast<char>(idx))
+                            : (charset[table[idx]] == idx)) &&
+      (idx > 0 ? checkReverseIndex(idx - 1, charset, base, table) : true);
+}
+
+} // namespace facebook::velox::encoding