buffer: add Buffer.prototype.lastIndexOf()

* Remove unnecessary templating from SearchString

  SearchString used to have separate PatternChar and SubjectChar template type
  arguments, apparently to support things like searching for an 8-bit string
  inside a 16-bit string or vice versa. However, SearchString is only used from
  node_buffer.cc, where PatternChar and SubjectChar are always the same. Since
  this is extra complexity that's unused and untested (simplifying to a single
  Char template argument still compiles and didn't break any unit tests), I
  removed it.

* Use Boyer-Hoore[-Horspool] for both indexOf and lastIndexOf

  Add test cases for lastIndexOf. Test the fallback from BMH to
  Boyer-Moore, which looks like it was totally untested before.

* Extra bounds checks in node_buffer.cc

* Extra asserts in string_search.h

* Buffer.lastIndexOf: clean up, enforce consistency w/ String.lastIndexOf

* Polyfill memrchr(3) for non-GNU systems

PR-URL: https://github.com/nodejs/node/pull/4846
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

doc/api/buffer.md

@@ -988,6 +988,46 @@ for (var key of buf.keys()) {
 //   5
 ```
 
+### buf.lastIndexOf(value[, byteOffset][, encoding])
+
+* `value` {String|Buffer|Number}
+* `byteOffset` {Number} Default: `buf.length`
+* `encoding` {String} Default: `'utf8'`
+* Return: {Number}
+
+Identical to [`Buffer#indexOf()`][], but searches the Buffer from back to front
+instead of front to back. Returns the starting index position of `value` in
+Buffer or `-1` if the Buffer does not contain `value`. The `value` can be a
+String, Buffer or Number. Strings are by default interpreted as UTF8. If
+`byteOffset` is provided, will return the last match that begins at or before
+`byteOffset`.
+
+```js
+const buf = new Buffer('this buffer is a buffer');
+
+buf.lastIndexOf('this');
+  // returns 0
+buf.lastIndexOf('buffer');
+  // returns 17
+buf.lastIndexOf(new Buffer('buffer'));
+  // returns 17
+buf.lastIndexOf(97); // ascii for 'a'
+  // returns 15
+buf.lastIndexOf(new Buffer('yolo'));
+  // returns -1
+buf.lastIndexOf('buffer', 5)
+  // returns 5
+buf.lastIndexOf('buffer', 4)
+  // returns -1
+
+const utf16Buffer = new Buffer('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
+
+utf16Buffer.lastIndexOf('\u03a3', null, 'ucs2');
+  // returns 6
+utf16Buffer.lastIndexOf('\u03a3', -5, 'ucs2');
+  // returns 4
+```
+
 ### buf.length
 
 * {Number}

lib/buffer.js

@@ -598,7 +598,48 @@ Buffer.prototype.compare = function compare(target,
   return binding.compareOffset(this, target, start, thisStart, end, thisEnd);
 };
 
-function slowIndexOf(buffer, val, byteOffset, encoding) {
+
+// Finds either the first index of `val` in `buffer` at offset >= `byteOffset`,
+// OR the last index of `val` in `buffer` at offset <= `byteOffset`.
+//
+// Arguments:
+// - buffer - a Buffer to search
+// - val - a string, Buffer, or number
+// - byteOffset - an index into `buffer`; will be clamped to an int32
+// - encoding - an optional encoding, relevant is val is a string
+// - dir - true for indexOf, false for lastIndexOf
+function bidirectionalIndexOf(buffer, val, byteOffset, encoding, dir) {
+  if (typeof byteOffset === 'string') {
+    encoding = byteOffset;
+    byteOffset = undefined;
+  } else if (byteOffset > 0x7fffffff) {
+    byteOffset = 0x7fffffff;
+  } else if (byteOffset < -0x80000000) {
+    byteOffset = -0x80000000;
+  }
+  byteOffset = +byteOffset;  // Coerce to Number.
+  if (isNaN(byteOffset)) {
+    // If the offset is undefined, null, NaN, "foo", etc, search whole buffer.
+    byteOffset = dir ? 0 : (buffer.length - 1);
+  }
+  dir = !!dir;  // Cast to bool.
+
+  if (typeof val === 'string') {
+    if (encoding === undefined) {
+      return binding.indexOfString(buffer, val, byteOffset, encoding, dir);
+    }
+    return slowIndexOf(buffer, val, byteOffset, encoding, dir);
+  } else if (val instanceof Buffer) {
+    return binding.indexOfBuffer(buffer, val, byteOffset, encoding, dir);
+  } else if (typeof val === 'number') {
+    return binding.indexOfNumber(buffer, val, byteOffset, dir);
+  }
+
+  throw new TypeError('"val" argument must be string, number or Buffer');
+}
+
+
+function slowIndexOf(buffer, val, byteOffset, encoding, dir) {
   var loweredCase = false;
   for (;;) {
     switch (encoding) {
@@ -609,13 +650,13 @@ function slowIndexOf(buffer, val, byteOffset, encoding) {
       case 'utf16le':
       case 'utf-16le':
       case 'binary':
-        return binding.indexOfString(buffer, val, byteOffset, encoding);
+        return binding.indexOfString(buffer, val, byteOffset, encoding, dir);
 
       case 'base64':
       case 'ascii':
       case 'hex':
         return binding.indexOfBuffer(
-            buffer, Buffer.from(val, encoding), byteOffset, encoding);
+            buffer, Buffer.from(val, encoding), byteOffset, encoding, dir);
 
       default:
         if (loweredCase) {
@@ -628,29 +669,14 @@ function slowIndexOf(buffer, val, byteOffset, encoding) {
   }
 }
 
+
 Buffer.prototype.indexOf = function indexOf(val, byteOffset, encoding) {
-  if (typeof byteOffset === 'string') {
-    encoding = byteOffset;
-    byteOffset = 0;
-  } else if (byteOffset > 0x7fffffff) {
-    byteOffset = 0x7fffffff;
-  } else if (byteOffset < -0x80000000) {
-    byteOffset = -0x80000000;
-  }
-  byteOffset >>= 0;
+  return bidirectionalIndexOf(this, val, byteOffset, encoding, true);
+};
 
-  if (typeof val === 'string') {
-    if (encoding === undefined) {
-      return binding.indexOfString(this, val, byteOffset, encoding);
-    }
-    return slowIndexOf(this, val, byteOffset, encoding);
-  } else if (val instanceof Buffer) {
-    return binding.indexOfBuffer(this, val, byteOffset, encoding);
-  } else if (typeof val === 'number') {
-    return binding.indexOfNumber(this, val, byteOffset);
-  }
 
-  throw new TypeError('"val" argument must be string, number or Buffer');
+Buffer.prototype.lastIndexOf = function lastIndexOf(val, byteOffset, encoding) {
+  return bidirectionalIndexOf(this, val, byteOffset, encoding, false);
 };
 
 

src/node_buffer.cc

@@ -943,9 +943,44 @@ void Compare(const FunctionCallbackInfo<Value> &args) {
 }
 
 
+// Computes the offset for starting an indexOf or lastIndexOf search.
+// Returns either a valid offset in [0...<length - 1>], ie inside the Buffer,
+// or -1 to signal that there is no possible match.
+int64_t IndexOfOffset(size_t length, int64_t offset_i64, bool is_forward) {
+  int64_t length_i64 = static_cast<int64_t>(length);
+  if (length_i64 == 0) {
+    // Empty buffer, no match.
+    return -1;
+  }
+  if (offset_i64 < 0) {
+    if (offset_i64 + length_i64 >= 0) {
+      // Negative offsets count backwards from the end of the buffer.
+      return length_i64 + offset_i64;
+    } else if (is_forward) {
+      // indexOf from before the start of the buffer: search the whole buffer.
+      return 0;
+    } else {
+      // lastIndexOf from before the start of the buffer: no match.
+      return -1;
+    }
+  } else {
+    if (offset_i64 < length_i64) {
+      // Valid positive offset.
+      return offset_i64;
+    } else if (is_forward) {
+      // indexOf from past the end of the buffer: no match.
+      return -1;
+    } else {
+      // lastIndexOf from past the end of the buffer: search the whole buffer.
+      return length_i64 - 1;
+    }
+  }
+}
+
 void IndexOfString(const FunctionCallbackInfo<Value>& args) {
   ASSERT(args[1]->IsString());
   ASSERT(args[2]->IsNumber());
+  ASSERT(args[4]->IsBoolean());
 
   enum encoding enc = ParseEncoding(args.GetIsolate(),
                                     args[3],
@@ -955,31 +990,26 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
   SPREAD_ARG(args[0], ts_obj);
 
   Local<String> needle = args[1].As<String>();
+  int64_t offset_i64 = args[2]->IntegerValue();
+  bool is_forward = args[4]->IsTrue();
+
   const char* haystack = ts_obj_data;
   const size_t haystack_length = ts_obj_length;
   // Extended latin-1 characters are 2 bytes in Utf8.
   const size_t needle_length =
       enc == BINARY ? needle->Length() : needle->Utf8Length();
 
-
   if (needle_length == 0 || haystack_length == 0) {
     return args.GetReturnValue().Set(-1);
   }
 
-  int64_t offset_i64 = args[2]->IntegerValue();
-  size_t offset = 0;
-
-  if (offset_i64 < 0) {
-    if (offset_i64 + static_cast<int64_t>(haystack_length) < 0) {
-      offset = 0;
-    } else {
-      offset = static_cast<size_t>(haystack_length + offset_i64);
-    }
-  } else {
-    offset = static_cast<size_t>(offset_i64);
+  int64_t opt_offset = IndexOfOffset(haystack_length, offset_i64, is_forward);
+  if (opt_offset <= -1) {
+    return args.GetReturnValue().Set(-1);
   }
-
-  if (haystack_length < offset || needle_length + offset > haystack_length) {
+  size_t offset = static_cast<size_t>(opt_offset);
+  CHECK_LT(offset, haystack_length);
+  if (is_forward && needle_length + offset > haystack_length) {
     return args.GetReturnValue().Set(-1);
   }
 
@@ -1007,13 +1037,15 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
                             haystack_length / 2,
                             decoded_string,
                             decoder.size() / 2,
-                            offset / 2);
+                            offset / 2,
+                            is_forward);
     } else {
       result = SearchString(reinterpret_cast<const uint16_t*>(haystack),
                             haystack_length / 2,
                             reinterpret_cast<const uint16_t*>(*needle_value),
                             needle_value.length(),
-                            offset / 2);
+                            offset / 2,
+                            is_forward);
     }
     result *= 2;
   } else if (enc == UTF8) {
@@ -1025,7 +1057,8 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
                           haystack_length,
                           reinterpret_cast<const uint8_t*>(*needle_value),
                           needle_length,
-                          offset);
+                          offset,
+                          is_forward);
   } else if (enc == BINARY) {
     uint8_t* needle_data = static_cast<uint8_t*>(malloc(needle_length));
     if (needle_data == nullptr) {
@@ -1038,7 +1071,8 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
                           haystack_length,
                           needle_data,
                           needle_length,
-                          offset);
+                          offset,
+                          is_forward);
     free(needle_data);
   }
 
@@ -1049,17 +1083,18 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
 void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
   ASSERT(args[1]->IsObject());
   ASSERT(args[2]->IsNumber());
+  ASSERT(args[4]->IsBoolean());
 
   enum encoding enc = ParseEncoding(args.GetIsolate(),
                                     args[3],
                                     UTF8);
 
   THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
+  THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[1]);
   SPREAD_ARG(args[0], ts_obj);
   SPREAD_ARG(args[1], buf);
-
-  if (buf_length > 0)
-    CHECK_NE(buf_data, nullptr);
+  int64_t offset_i64 = args[2]->IntegerValue();
+  bool is_forward = args[4]->IsTrue();
 
   const char* haystack = ts_obj_data;
   const size_t haystack_length = ts_obj_length;
@@ -1070,19 +1105,13 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
     return args.GetReturnValue().Set(-1);
   }
 
-  int64_t offset_i64 = args[2]->IntegerValue();
-  size_t offset = 0;
-
-  if (offset_i64 < 0) {
-    if (offset_i64 + static_cast<int64_t>(haystack_length) < 0)
-      offset = 0;
-    else
-      offset = static_cast<size_t>(haystack_length + offset_i64);
-  } else {
-    offset = static_cast<size_t>(offset_i64);
+  int64_t opt_offset = IndexOfOffset(haystack_length, offset_i64, is_forward);
+  if (opt_offset <= -1) {
+    return args.GetReturnValue().Set(-1);
   }
-
-  if (haystack_length < offset || needle_length + offset > haystack_length) {
+  size_t offset = static_cast<size_t>(opt_offset);
+  CHECK_LT(offset, haystack_length);
+  if (is_forward && needle_length + offset > haystack_length) {
     return args.GetReturnValue().Set(-1);
   }
 
@@ -1097,7 +1126,8 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
         haystack_length / 2,
         reinterpret_cast<const uint16_t*>(needle),
         needle_length / 2,
-        offset / 2);
+        offset / 2,
+        is_forward);
     result *= 2;
   } else {
     result = SearchString(
@@ -1105,7 +1135,8 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
         haystack_length,
         reinterpret_cast<const uint8_t*>(needle),
         needle_length,
-        offset);
+        offset,
+        is_forward);
   }
 
   args.GetReturnValue().Set(
@@ -1115,28 +1146,29 @@ void IndexOfBuffer(const FunctionCallbackInfo<Value>& args) {
 void IndexOfNumber(const FunctionCallbackInfo<Value>& args) {
   ASSERT(args[1]->IsNumber());
   ASSERT(args[2]->IsNumber());
+  ASSERT(args[3]->IsBoolean());
 
   THROW_AND_RETURN_UNLESS_BUFFER(Environment::GetCurrent(args), args[0]);
   SPREAD_ARG(args[0], ts_obj);
 
   uint32_t needle = args[1]->Uint32Value();
   int64_t offset_i64 = args[2]->IntegerValue();
-  size_t offset;
-
-  if (offset_i64 < 0) {
-    if (offset_i64 + static_cast<int64_t>(ts_obj_length) < 0)
-      offset = 0;
-    else
-      offset = static_cast<size_t>(ts_obj_length + offset_i64);
-  } else {
-    offset = static_cast<size_t>(offset_i64);
-  }
+  bool is_forward = args[3]->IsTrue();
 
-  if (ts_obj_length == 0 || offset + 1 > ts_obj_length)
+  int64_t opt_offset = IndexOfOffset(ts_obj_length, offset_i64, is_forward);
+  if (opt_offset <= -1) {
     return args.GetReturnValue().Set(-1);
+  }
+  size_t offset = static_cast<size_t>(opt_offset);
+  CHECK_LT(offset, ts_obj_length);
 
-  void* ptr = memchr(ts_obj_data + offset, needle, ts_obj_length - offset);
-  char* ptr_char = static_cast<char*>(ptr);
+  const void* ptr;
+  if (is_forward) {
+    ptr = memchr(ts_obj_data + offset, needle, ts_obj_length - offset);
+  } else {
+    ptr = node::stringsearch::MemrchrFill(ts_obj_data, needle, offset + 1);
+  }
+  const char* ptr_char = static_cast<const char*>(ptr);
   args.GetReturnValue().Set(ptr ? static_cast<int>(ptr_char - ts_obj_data)
                                 : -1);
 }

src/string_search.h

@@ -21,60 +21,35 @@ T Max(T a, T b) {
 
 static const uint32_t kMaxOneByteCharCodeU = 0xff;
 
-
-static inline size_t NonOneByteStart(const uint16_t* chars, size_t length) {
-  const uint16_t* limit = chars + length;
-  const uint16_t* start = chars;
-  while (chars < limit) {
-    if (*chars > kMaxOneByteCharCodeU)
-      return static_cast<size_t>(chars - start);
-    ++chars;
-  }
-  return static_cast<size_t>(chars - start);
-}
-
-
-static inline bool IsOneByte(const uint16_t* chars, size_t length) {
-  return NonOneByteStart(chars, length) >= length;
-}
-
-
 template <typename T>
 class Vector {
  public:
-  Vector(T* data, size_t length) : start_(data), length_(length) {
+  Vector(T* data, size_t length, bool isForward)
+      : start_(data), length_(length), is_forward_(isForward) {
     ASSERT(length > 0 && data != nullptr);
   }
 
-  // Returns the length of the vector.
+  // Returns the start of the memory range.
+  // For vector v this is NOT necessarily &v[0], see forward().
+  const T* start() const { return start_; }
+
+  // Returns the length of the vector, in characters.
   size_t length() const { return length_; }
 
-  T* start() const { return start_; }
+  // Returns true if the Vector is front-to-back, false if back-to-front.
+  // In the latter case, v[0] corresponds to the *end* of the memory range.
+  size_t forward() const { return is_forward_; }
 
   // Access individual vector elements - checks bounds in debug mode.
   T& operator[](size_t index) const {
     ASSERT(0 <= index && index < length_);
-    return start_[index];
-  }
-
-  const T& at(size_t index) const { return operator[](index); }
-
-  bool operator==(const Vector<T>& other) const {
-    if (length_ != other.length_)
-      return false;
-    if (start_ == other.start_)
-      return true;
-    for (size_t i = 0; i < length_; ++i) {
-      if (start_[i] != other.start_[i]) {
-        return false;
-      }
-    }
-    return true;
+    return start_[is_forward_ ? index : (length_ - index - 1)];
   }
 
  private:
   T* start_;
   size_t length_;
+  bool is_forward_;
 };
 
 
@@ -114,31 +89,17 @@ class StringSearchBase {
   // Table used temporarily while building the BoyerMoore good suffix
   // shift table.
   static int kSuffixTable[kBMMaxShift + 1];
-
-  static inline bool IsOneByteString(Vector<const uint8_t> string) {
-    return true;
-  }
-
-  static inline bool IsOneByteString(Vector<const uint16_t> string) {
-    return IsOneByte(string.start(), string.length());
-  }
 };
 
-template <typename PatternChar, typename SubjectChar>
+template <typename Char>
 class StringSearch : private StringSearchBase {
  public:
-  explicit StringSearch(Vector<const PatternChar> pattern)
+  explicit StringSearch(Vector<const Char> pattern)
       : pattern_(pattern), start_(0) {
     if (pattern.length() >= kBMMaxShift) {
       start_ = pattern.length() - kBMMaxShift;
     }
 
-    if (sizeof(PatternChar) > sizeof(SubjectChar)) {
-      if (!IsOneByteString(pattern_)) {
-        strategy_ = &FailSearch;
-        return;
-      }
-    }
     size_t pattern_length = pattern_.length();
     CHECK_GT(pattern_length, 0);
     if (pattern_length < kBMMinPatternLength) {
@@ -152,12 +113,12 @@ class StringSearch : private StringSearchBase {
     strategy_ = &InitialSearch;
   }
 
-  size_t Search(Vector<const SubjectChar> subject, size_t index) {
+  size_t Search(Vector<const Char> subject, size_t index) {
     return strategy_(this, subject, index);
   }
 
   static inline int AlphabetSize() {
-    if (sizeof(PatternChar) == 1) {
+    if (sizeof(Char) == 1) {
       // Latin1 needle.
       return kLatin1AlphabetSize;
     } else {
@@ -165,42 +126,42 @@ class StringSearch : private StringSearchBase {
       return kUC16AlphabetSize;
     }
 
-    static_assert(sizeof(PatternChar) == sizeof(uint8_t) ||
-                      sizeof(PatternChar) == sizeof(uint16_t),
-                  "sizeof(PatternChar) == sizeof(uint16_t) || sizeof(uint8_t)");
+    static_assert(sizeof(Char) == sizeof(uint8_t) ||
+                  sizeof(Char) == sizeof(uint16_t),
+                  "sizeof(Char) == sizeof(uint16_t) || sizeof(uint8_t)");
   }
 
  private:
   typedef size_t (*SearchFunction)(  // NOLINT - it's not a cast!
-      StringSearch<PatternChar, SubjectChar>*,
-      Vector<const SubjectChar>,
+      StringSearch<Char>*,
+      Vector<const Char>,
       size_t);
 
-  static size_t FailSearch(StringSearch<PatternChar, SubjectChar>*,
-                           Vector<const SubjectChar> subject,
+  static size_t FailSearch(StringSearch<Char>*,
+                           Vector<const Char> subject,
                            size_t) {
     return subject.length();
   }
 
-  static size_t SingleCharSearch(StringSearch<PatternChar, SubjectChar>* search,
-                                 Vector<const SubjectChar> subject,
+  static size_t SingleCharSearch(StringSearch<Char>* search,
+                                 Vector<const Char> subject,
                                  size_t start_index);
 
-  static size_t LinearSearch(StringSearch<PatternChar, SubjectChar>* search,
-                             Vector<const SubjectChar> subject,
+  static size_t LinearSearch(StringSearch<Char>* search,
+                             Vector<const Char> subject,
                              size_t start_index);
 
-  static size_t InitialSearch(StringSearch<PatternChar, SubjectChar>* search,
-                              Vector<const SubjectChar> subject,
+  static size_t InitialSearch(StringSearch<Char>* search,
+                              Vector<const Char> subject,
                               size_t start_index);
 
   static size_t BoyerMooreHorspoolSearch(
-      StringSearch<PatternChar, SubjectChar>* search,
-      Vector<const SubjectChar> subject,
+      StringSearch<Char>* search,
+      Vector<const Char> subject,
       size_t start_index);
 
-  static size_t BoyerMooreSearch(StringSearch<PatternChar, SubjectChar>* search,
-                                 Vector<const SubjectChar> subject,
+  static size_t BoyerMooreSearch(StringSearch<Char>* search,
+                                 Vector<const Char> subject,
                                  size_t start_index);
 
   void PopulateBoyerMooreHorspoolTable();
@@ -214,16 +175,10 @@ class StringSearch : private StringSearchBase {
   }
 
   static inline int CharOccurrence(int* bad_char_occurrence,
-                                   SubjectChar char_code) {
-    if (sizeof(SubjectChar) == 1) {
+                                   Char char_code) {
+    if (sizeof(Char) == 1) {
       return bad_char_occurrence[static_cast<int>(char_code)];
     }
-    if (sizeof(PatternChar) == 1) {
-      if (exceedsOneByte(char_code)) {
-        return -1;
-      }
-      return bad_char_occurrence[static_cast<unsigned int>(char_code)];
-    }
     // Both pattern and subject are UC16. Reduce character to equivalence class.
     int equiv_class = char_code % kUC16AlphabetSize;
     return bad_char_occurrence[equiv_class];
@@ -250,7 +205,7 @@ class StringSearch : private StringSearchBase {
   }
 
   // The pattern to search for.
-  Vector<const PatternChar> pattern_;
+  Vector<const Char> pattern_;
   // Pointer to implementation of the search.
   SearchFunction strategy_;
   // Cache value of Max(0, pattern_length() - kBMMaxShift)
@@ -274,111 +229,138 @@ inline uint8_t GetHighestValueByte(uint16_t character) {
 inline uint8_t GetHighestValueByte(uint8_t character) { return character; }
 
 
-template <typename PatternChar, typename SubjectChar>
-inline size_t FindFirstCharacter(Vector<const PatternChar> pattern,
-                              Vector<const SubjectChar> subject, size_t index) {
-  const PatternChar pattern_first_char = pattern[0];
+// Searches for a byte value in a memory buffer, back to front.
+// Uses memrchr(3) on systems which support it, for speed.
+// Falls back to a vanilla for loop on non-GNU systems such as Windows.
+inline const void* MemrchrFill(const void* haystack, uint8_t needle,
+                               size_t haystack_len) {
+#ifdef _GNU_SOURCE
+  return memrchr(haystack, needle, haystack_len);
+#else
+  const uint8_t* haystack8 = static_cast<const uint8_t*>(haystack);
+  for (size_t i = haystack_len - 1; i != static_cast<size_t>(-1); i--) {
+    if (haystack8[i] == needle) {
+      return haystack8 + i;
+    }
+  }
+  return nullptr;
+#endif
+}
+
+
+// Finds the first occurence of *two-byte* character pattern[0] in the string
+// `subject`. Does not check that the whole pattern matches.
+template <typename Char>
+inline size_t FindFirstCharacter(Vector<const Char> pattern,
+                              Vector<const Char> subject, size_t index) {
+  const Char pattern_first_char = pattern[0];
   const size_t max_n = (subject.length() - pattern.length() + 1);
 
+  // For speed, search for the more `rare` of the two bytes in pattern[0]
+  // using memchr / memrchr (which are much faster than a simple for loop).
   const uint8_t search_byte = GetHighestValueByte(pattern_first_char);
-  const SubjectChar search_char = static_cast<SubjectChar>(pattern_first_char);
   size_t pos = index;
   do {
-    const SubjectChar* char_pos = reinterpret_cast<const SubjectChar*>(
-        memchr(subject.start() + pos, search_byte,
-               (max_n - pos) * sizeof(SubjectChar)));
+    size_t bytes_to_search;
+    const void* void_pos;
+    if (subject.forward()) {
+      // Assert that bytes_to_search won't overflow
+      CHECK_LE(pos, max_n);
+      CHECK_LE(max_n - pos, SIZE_MAX / sizeof(Char));
+      bytes_to_search = (max_n - pos) * sizeof(Char);
+      void_pos = memchr(subject.start() + pos, search_byte, bytes_to_search);
+    } else {
+      CHECK_LE(pos, subject.length());
+      CHECK_LE(subject.length() - pos, SIZE_MAX / sizeof(Char));
+      bytes_to_search = (subject.length() - pos) * sizeof(Char);
+      void_pos = MemrchrFill(subject.start(), search_byte, bytes_to_search);
+    }
+    const Char* char_pos = static_cast<const Char*>(void_pos);
     if (char_pos == nullptr)
       return subject.length();
-    char_pos = AlignDown(char_pos, sizeof(SubjectChar));
-    pos = static_cast<size_t>(char_pos - subject.start());
-    if (subject[pos] == search_char)
+
+    // Then, for each match, verify that the full two bytes match pattern[0].
+    char_pos = AlignDown(char_pos, sizeof(Char));
+    size_t raw_pos = static_cast<size_t>(char_pos - subject.start());
+    pos = subject.forward() ? raw_pos : (subject.length() - raw_pos - 1);
+    if (subject[pos] == pattern_first_char) {
+      // Match found, hooray.
       return pos;
+    }
+    // Search byte matched, but the other byte of pattern[0] didn't. Keep going.
   } while (++pos < max_n);
 
   return subject.length();
 }
 
 
+// Finds the first occurance of the byte pattern[0] in string `subject`.
+// Does not verify that the whole pattern matches.
 template <>
 inline size_t FindFirstCharacter(Vector<const uint8_t> pattern,
                                  Vector<const uint8_t> subject,
                                  size_t index) {
   const uint8_t pattern_first_char = pattern[0];
+  const size_t subj_len = subject.length();
   const size_t max_n = (subject.length() - pattern.length() + 1);
 
-  const uint8_t* char_pos = reinterpret_cast<const uint8_t*>(
-      memchr(subject.start() + index, pattern_first_char, max_n - index));
-  if (char_pos == nullptr)
-    return subject.length();
-  return static_cast<size_t>(char_pos - subject.start());
+  const void* pos;
+  if (subject.forward()) {
+    pos = memchr(subject.start() + index, pattern_first_char, max_n - index);
+  } else {
+    pos = MemrchrFill(subject.start(), pattern_first_char, subj_len - index);
+  }
+  const uint8_t* char_pos = static_cast<const uint8_t*>(pos);
+  if (char_pos == nullptr) {
+    return subj_len;
+  }
+
+  size_t raw_pos = static_cast<size_t>(char_pos - subject.start());
+  return subject.forward() ? raw_pos : (subj_len - raw_pos - 1);
 }
 
 //---------------------------------------------------------------------
 // Single Character Pattern Search Strategy
 //---------------------------------------------------------------------
 
-template <typename PatternChar, typename SubjectChar>
-size_t StringSearch<PatternChar, SubjectChar>::SingleCharSearch(
-    StringSearch<PatternChar, SubjectChar>* search,
-    Vector<const SubjectChar> subject,
+template <typename Char>
+size_t StringSearch<Char>::SingleCharSearch(
+    StringSearch<Char>* search,
+    Vector<const Char> subject,
     size_t index) {
   CHECK_EQ(1, search->pattern_.length());
-  PatternChar pattern_first_char = search->pattern_[0];
-
-  if (sizeof(SubjectChar) == 1 && sizeof(PatternChar) == 1) {
-    return FindFirstCharacter(search->pattern_, subject, index);
-  } else {
-    if (sizeof(PatternChar) > sizeof(SubjectChar)) {
-      if (exceedsOneByte(pattern_first_char)) {
-        return -1;
-      }
-    }
-    return FindFirstCharacter(search->pattern_, subject, index);
-  }
+  return FindFirstCharacter(search->pattern_, subject, index);
 }
 
 //---------------------------------------------------------------------
 // Linear Search Strategy
 //---------------------------------------------------------------------
 
-template <typename PatternChar, typename SubjectChar>
-inline bool CharCompare(const PatternChar* pattern,
-                        const SubjectChar* subject,
-                        size_t length) {
-  ASSERT_GT(length, 0);
-  size_t pos = 0;
-  do {
-    if (pattern[pos] != subject[pos]) {
-      return false;
-    }
-    pos++;
-  } while (pos < length);
-  return true;
-}
-
 // Simple linear search for short patterns. Never bails out.
-template <typename PatternChar, typename SubjectChar>
-size_t StringSearch<PatternChar, SubjectChar>::LinearSearch(
-    StringSearch<PatternChar, SubjectChar>* search,
-    Vector<const SubjectChar> subject,
+template <typename Char>
+size_t StringSearch<Char>::LinearSearch(
+    StringSearch<Char>* search,
+    Vector<const Char> subject,
     size_t index) {
-  Vector<const PatternChar> pattern = search->pattern_;
+  Vector<const Char> pattern = search->pattern_;
   CHECK_GT(pattern.length(), 1);
   const size_t pattern_length = pattern.length();
-  size_t i = index;
   const size_t n = subject.length() - pattern_length;
-  while (i <= n) {
+  for (size_t i = index; i <= n; i++) {
     i = FindFirstCharacter(pattern, subject, i);
     if (i == subject.length())
       return subject.length();
     ASSERT_LE(i, n);
-    i++;
 
-    // Loop extracted to separate function to allow using return to do
-    // a deeper break.
-    if (CharCompare(pattern.start() + 1, subject.start() + i,
-                    pattern_length - 1)) {
-      return i - 1;
+    bool matches = true;
+    for (size_t j = 1; j < pattern_length; j++) {
+      if (pattern[j] != subject[i + j]) {
+        matches = false;
+        break;
+      }
+    }
+    if (matches) {
+      return i;
     }
   }
   return subject.length();
@@ -388,12 +370,12 @@ size_t StringSearch<PatternChar, SubjectChar>::LinearSearch(
 // Boyer-Moore string search
 //---------------------------------------------------------------------
 
-template <typename PatternChar, typename SubjectChar>
-size_t StringSearch<PatternChar, SubjectChar>::BoyerMooreSearch(
-    StringSearch<PatternChar, SubjectChar>* search,
-    Vector<const SubjectChar> subject,
+template <typename Char>
+size_t StringSearch<Char>::BoyerMooreSearch(
+    StringSearch<Char>* search,
+    Vector<const Char> subject,
     size_t start_index) {
-  Vector<const PatternChar> pattern = search->pattern_;
+  Vector<const Char> pattern = search->pattern_;
   const size_t subject_length = subject.length();
   const size_t pattern_length = pattern.length();
   // Only preprocess at most kBMMaxShift last characters of pattern.
@@ -402,7 +384,7 @@ size_t StringSearch<PatternChar, SubjectChar>::BoyerMooreSearch(
   int* bad_char_occurence = search->bad_char_table();
   int* good_suffix_shift = search->good_suffix_shift_table();
 
-  PatternChar last_char = pattern[pattern_length - 1];
+  Char last_char = pattern[pattern_length - 1];
   size_t index = start_index;
   // Continue search from i.
   while (index <= subject_length - pattern_length) {
@@ -426,7 +408,7 @@ size_t StringSearch<PatternChar, SubjectChar>::BoyerMooreSearch(
       // Fall back on BMH shift.
       index += pattern_length - 1 -
                CharOccurrence(bad_char_occurence,
-                              static_cast<SubjectChar>(last_char));
+                              static_cast<Char>(last_char));
     } else {
       int gs_shift = good_suffix_shift[j + 1];
       int bc_occ = CharOccurrence(bad_char_occurence, c);
@@ -441,10 +423,10 @@ size_t StringSearch<PatternChar, SubjectChar>::BoyerMooreSearch(
   return subject.length();
 }
 
-template <typename PatternChar, typename SubjectChar>
-void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreTable() {
+template <typename Char>
+void StringSearch<Char>::PopulateBoyerMooreTable() {
   const size_t pattern_length = pattern_.length();
-  const PatternChar* pattern = pattern_.start();
+  Vector<const Char> pattern = pattern_;
   // Only look at the last kBMMaxShift characters of pattern (from start_
   // to pattern_length).
   const size_t start = start_;
@@ -467,12 +449,12 @@ void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreTable() {
   }
 
   // Find suffixes.
-  PatternChar last_char = pattern[pattern_length - 1];
+  Char last_char = pattern_[pattern_length - 1];
   size_t suffix = pattern_length + 1;
   {
     size_t i = pattern_length;
     while (i > start) {
-      PatternChar c = pattern[i - 1];
+      Char c = pattern[i - 1];
       while (suffix <= pattern_length && c != pattern[suffix - 1]) {
         if (static_cast<size_t>(shift_table[suffix]) == length) {
           shift_table[suffix] = suffix - i;
@@ -511,22 +493,22 @@ void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreTable() {
 // Boyer-Moore-Horspool string search.
 //---------------------------------------------------------------------
 
-template <typename PatternChar, typename SubjectChar>
-size_t StringSearch<PatternChar, SubjectChar>::BoyerMooreHorspoolSearch(
-    StringSearch<PatternChar, SubjectChar>* search,
-    Vector<const SubjectChar> subject,
+template <typename Char>
+size_t StringSearch<Char>::BoyerMooreHorspoolSearch(
+    StringSearch<Char>* search,
+    Vector<const Char> subject,
     size_t start_index) {
-  Vector<const PatternChar> pattern = search->pattern_;
+  Vector<const Char> pattern = search->pattern_;
   const size_t subject_length = subject.length();
   const size_t pattern_length = pattern.length();
   int* char_occurrences = search->bad_char_table();
   int64_t badness = -pattern_length;
 
   // How bad we are doing without a good-suffix table.
-  PatternChar last_char = pattern[pattern_length - 1];
+  Char last_char = pattern[pattern_length - 1];
   int last_char_shift =
       pattern_length - 1 -
-      CharOccurrence(char_occurrences, static_cast<SubjectChar>(last_char));
+      CharOccurrence(char_occurrences, static_cast<Char>(last_char));
 
   // Perform search
   size_t index = start_index;  // No matches found prior to this index.
@@ -564,8 +546,8 @@ size_t StringSearch<PatternChar, SubjectChar>::BoyerMooreHorspoolSearch(
   return subject.length();
 }
 
-template <typename PatternChar, typename SubjectChar>
-void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreHorspoolTable() {
+template <typename Char>
+void StringSearch<Char>::PopulateBoyerMooreHorspoolTable() {
   const size_t pattern_length = pattern_.length();
 
   int* bad_char_occurrence = bad_char_table();
@@ -585,8 +567,8 @@ void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreHorspoolTable() {
     }
   }
   for (size_t i = start; i < pattern_length - 1; i++) {
-    PatternChar c = pattern_[i];
-    int bucket = (sizeof(PatternChar) == 1) ? c : c % AlphabetSize();
+    Char c = pattern_[i];
+    int bucket = (sizeof(Char) == 1) ? c : c % AlphabetSize();
     bad_char_occurrence[bucket] = i;
   }
 }
@@ -597,12 +579,12 @@ void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreHorspoolTable() {
 
 // Simple linear search for short patterns, which bails out if the string
 // isn't found very early in the subject. Upgrades to BoyerMooreHorspool.
-template <typename PatternChar, typename SubjectChar>
-size_t StringSearch<PatternChar, SubjectChar>::InitialSearch(
-    StringSearch<PatternChar, SubjectChar>* search,
-    Vector<const SubjectChar> subject,
+template <typename Char>
+size_t StringSearch<Char>::InitialSearch(
+    StringSearch<Char>* search,
+    Vector<const Char> subject,
     size_t index) {
-  Vector<const PatternChar> pattern = search->pattern_;
+  Vector<const Char> pattern = search->pattern_;
   const size_t pattern_length = pattern.length();
   // Badness is a count of how much work we have done.  When we have
   // done enough work we decide it's probably worth switching to a better
@@ -642,11 +624,11 @@ size_t StringSearch<PatternChar, SubjectChar>::InitialSearch(
 // If searching multiple times for the same pattern, a search
 // object should be constructed once and the Search function then called
 // for each search.
-template <typename SubjectChar, typename PatternChar>
-size_t SearchString(Vector<const SubjectChar> subject,
-                    Vector<const PatternChar> pattern,
+template <typename Char>
+size_t SearchString(Vector<const Char> subject,
+                    Vector<const Char> pattern,
                     size_t start_index) {
-  StringSearch<PatternChar, SubjectChar> search(pattern);
+  StringSearch<Char> search(pattern);
   return search.Search(subject, start_index);
 }
 }
@@ -655,16 +637,38 @@ size_t SearchString(Vector<const SubjectChar> subject,
 namespace node {
 using node::stringsearch::Vector;
 
-template <typename SubjectChar, typename PatternChar>
-size_t SearchString(const SubjectChar* haystack,
+template <typename Char>
+size_t SearchString(const Char* haystack,
                     size_t haystack_length,
-                    const PatternChar* needle,
+                    const Char* needle,
                     size_t needle_length,
-                    size_t start_index) {
-  return node::stringsearch::SearchString(
-      Vector<const SubjectChar>(haystack, haystack_length),
-      Vector<const PatternChar>(needle, needle_length),
-      start_index);
+                    size_t start_index,
+                    bool is_forward) {
+  // To do a reverse search (lastIndexOf instead of indexOf) without redundant
+  // code, create two vectors that are reversed views into the input strings.
+  // For example, v_needle[0] would return the *last* character of the needle.
+  // So we're searching for the first instance of rev(needle) in rev(haystack)
+  Vector<const Char> v_needle = Vector<const Char>(
+      needle, needle_length, is_forward);
+  Vector<const Char> v_haystack = Vector<const Char>(
+      haystack, haystack_length, is_forward);
+  ASSERT(haystack_length >= needle_length);
+  size_t diff = haystack_length - needle_length;
+  size_t relative_start_index;
+  if (is_forward) {
+    relative_start_index = start_index;
+  } else if (diff < start_index) {
+    relative_start_index = 0;
+  } else {
+    relative_start_index = diff - start_index;
+  }
+  size_t pos = node::stringsearch::SearchString(
+      v_haystack, v_needle, relative_start_index);
+  if (pos == haystack_length) {
+    // not found
+    return pos;
+  }
+  return is_forward ? pos : (haystack_length - needle_length - pos);
 }
 }  // namespace node
 

test/parallel/test-buffer-indexof.js

@@ -282,3 +282,120 @@ assert.throws(function() {
 assert.throws(function() {
   b.indexOf([]);
 });
+
+// All code for handling encodings is shared between Buffer.indexOf and
+// Buffer.lastIndexOf, so only testing the separate lastIndexOf semantics.
+
+// Test lastIndexOf basic functionality; Buffer b contains 'abcdef'.
+// lastIndexOf string:
+assert.equal(b.lastIndexOf('a'), 0);
+assert.equal(b.lastIndexOf('a', 1), 0);
+assert.equal(b.lastIndexOf('b', 1), 1);
+assert.equal(b.lastIndexOf('c', 1), -1);
+assert.equal(b.lastIndexOf('a', -1), 0);
+assert.equal(b.lastIndexOf('a', -4), 0);
+assert.equal(b.lastIndexOf('a', -b.length), 0);
+assert.equal(b.lastIndexOf('a', -b.length - 1), -1);
+assert.equal(b.lastIndexOf('a', NaN), 0);
+assert.equal(b.lastIndexOf('a', -Infinity), -1);
+assert.equal(b.lastIndexOf('a', Infinity), 0);
+// lastIndexOf Buffer:
+assert.equal(b.lastIndexOf(buf_a), 0);
+assert.equal(b.lastIndexOf(buf_a, 1), 0);
+assert.equal(b.lastIndexOf(buf_a, -1), 0);
+assert.equal(b.lastIndexOf(buf_a, -4), 0);
+assert.equal(b.lastIndexOf(buf_a, -b.length), 0);
+assert.equal(b.lastIndexOf(buf_a, -b.length - 1), -1);
+assert.equal(b.lastIndexOf(buf_a, NaN), 0);
+assert.equal(b.lastIndexOf(buf_a, -Infinity), -1);
+assert.equal(b.lastIndexOf(buf_a, Infinity), 0);
+assert.equal(b.lastIndexOf(buf_bc), 1);
+assert.equal(b.lastIndexOf(buf_bc, 2), 1);
+assert.equal(b.lastIndexOf(buf_bc, -1), 1);
+assert.equal(b.lastIndexOf(buf_bc, -3), 1);
+assert.equal(b.lastIndexOf(buf_bc, -5), 1);
+assert.equal(b.lastIndexOf(buf_bc, -6), -1);
+assert.equal(b.lastIndexOf(buf_bc, NaN), 1);
+assert.equal(b.lastIndexOf(buf_bc, -Infinity), -1);
+assert.equal(b.lastIndexOf(buf_bc, Infinity), 1);
+assert.equal(b.lastIndexOf(buf_f), b.length - 1);
+assert.equal(b.lastIndexOf(buf_z), -1);
+assert.equal(b.lastIndexOf(buf_empty), -1);
+assert.equal(b.lastIndexOf(buf_empty, 1), -1);
+assert.equal(b.lastIndexOf(buf_empty, b.length + 1), -1);
+assert.equal(b.lastIndexOf(buf_empty, Infinity), -1);
+// lastIndexOf number:
+assert.equal(b.lastIndexOf(0x61), 0);
+assert.equal(b.lastIndexOf(0x61, 1), 0);
+assert.equal(b.lastIndexOf(0x61, -1), 0);
+assert.equal(b.lastIndexOf(0x61, -4), 0);
+assert.equal(b.lastIndexOf(0x61, -b.length), 0);
+assert.equal(b.lastIndexOf(0x61, -b.length - 1), -1);
+assert.equal(b.lastIndexOf(0x61, NaN), 0);
+assert.equal(b.lastIndexOf(0x61, -Infinity), -1);
+assert.equal(b.lastIndexOf(0x61, Infinity), 0);
+assert.equal(b.lastIndexOf(0x0), -1);
+
+// Test weird offset arguments.
+// Behaviour should match String.lastIndexOf:
+assert.equal(b.lastIndexOf('b', 0), -1);
+assert.equal(b.lastIndexOf('b', undefined), 1);
+assert.equal(b.lastIndexOf('b', null), -1);
+assert.equal(b.lastIndexOf('b', {}), 1);
+assert.equal(b.lastIndexOf('b', []), -1);
+assert.equal(b.lastIndexOf('b', [2]), 1);
+
+// Test lastIndexOf on a longer buffer:
+var bufferString = new Buffer('a man a plan a canal panama');
+assert.equal(15, bufferString.lastIndexOf('canal'));
+assert.equal(21, bufferString.lastIndexOf('panama'));
+assert.equal(0, bufferString.lastIndexOf('a man a plan a canal panama'));
+assert.equal(-1, bufferString.lastIndexOf('a man a plan a canal mexico'));
+assert.equal(13, bufferString.lastIndexOf('a '));
+assert.equal(13, bufferString.lastIndexOf('a ', 13));
+assert.equal(6, bufferString.lastIndexOf('a ', 12));
+assert.equal(0, bufferString.lastIndexOf('a ', 5));
+assert.equal(13, bufferString.lastIndexOf('a ', -1));
+assert.equal(0, bufferString.lastIndexOf('a ', -27));
+assert.equal(-1, bufferString.lastIndexOf('a ', -28));
+
+// The above tests test the LINEAR and SINGLE-CHAR strategies.
+// Now, we test the BOYER-MOORE-HORSPOOL strategy.
+// Test lastIndexOf on a long buffer w multiple matches:
+pattern = 'JABACABADABACABA';
+assert.equal(1535, longBufferString.lastIndexOf(pattern));
+assert.equal(1535, longBufferString.lastIndexOf(pattern, 1535));
+assert.equal(511, longBufferString.lastIndexOf(pattern, 1534));
+
+// Finally, give it a really long input to trigger fallback from BMH to
+// regular BOYER-MOORE (which has better worst-case complexity).
+
+// Generate a really long Thue-Morse sequence of 'yolo' and 'swag',
+// "yolo swag swag yolo swag yolo yolo swag" ..., goes on for about 5MB.
+// This is hard to search because it all looks similar, but never repeats.
+
+// countBits returns the number of bits in the binary reprsentation of n.
+function countBits(n) {
+  for (var count = 0; n > 0; count++) {
+    n = n & (n - 1); // remove top bit
+  }
+  return count;
+}
+var parts = [];
+for (var i = 0; i < 1000000; i++) {
+  parts.push((countBits(i) % 2 === 0) ? 'yolo' : 'swag');
+}
+var reallyLong = new Buffer(parts.join(' '));
+assert.equal('yolo swag swag yolo', reallyLong.slice(0, 19).toString());
+
+// Expensive reverse searches. Stress test lastIndexOf:
+pattern = reallyLong.slice(0, 100000);  // First 1/50th of the pattern.
+assert.equal(4751360, reallyLong.lastIndexOf(pattern));
+assert.equal(3932160, reallyLong.lastIndexOf(pattern, 4000000));
+assert.equal(2949120, reallyLong.lastIndexOf(pattern, 3000000));
+pattern = reallyLong.slice(100000, 200000);  // Second 1/50th.
+assert.equal(4728480, reallyLong.lastIndexOf(pattern));
+pattern = reallyLong.slice(0, 1000000);  // First 1/5th.
+assert.equal(3932160, reallyLong.lastIndexOf(pattern));
+pattern = reallyLong.slice(0, 2000000);  // first 2/5ths.
+assert.equal(0, reallyLong.lastIndexOf(pattern));