Refactor tokenizer

Summary: Prepare to add tiktoken

Test Plan:
Rely on CI jobs

Reviewers:

Subscribers:

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Author: larryliu0820

runner-et/CMakeLists.txt

@@ -34,8 +34,8 @@ set(_common_include_directories ${TORCHCHAT_ROOT}/${ET_BUILD_DIR}/src)
 cmake_print_variables(_common_include_directories)
 
 target_include_directories(executorch INTERFACE ${_common_include_directories}) # Ideally ExecuTorch installation process would do this
-add_executable(run run.cpp)
-
+add_executable(run run.cpp ${TORCHCHAT_ROOT}/runner/bpe_tokenizer.cpp)
+target_include_directories(run PRIVATE ${TORCHCHAT_ROOT}/runner)
 # Link ET runtime + extensions
 target_link_libraries(
   run PRIVATE
@@ -55,9 +55,6 @@ target_link_libraries(
 )
 target_link_options_shared_lib(optimized_native_cpu_ops_lib)
 target_link_options_shared_lib(xnnpack_backend)
-target_link_options_shared_lib(XNNPACK)
-target_link_options_shared_lib(pthreadpool)
-target_link_options_shared_lib(cpuinfo)
 # Not clear why linking executorch as whole-archive outside android/apple is leading
 # to double registration. Most likely because of linkage issues.
 # Will figure this out later. Until then use this.

runner/bpe_tokenizer.cpp

@@ -0,0 +1,318 @@
+#include <tokenizer.h>
+
+static int compare_tokens(const void* a, const void* b) {
+  if (((TokenIndex*)a)->str == nullptr) {
+    return -1;
+  }
+  if (((TokenIndex*)b)->str == nullptr) {
+    return 1;
+  }
+  return strcmp(((TokenIndex*)a)->str, ((TokenIndex*)b)->str);
+}
+
+BPETokenizer::BPETokenizer(
+    int32_t vocab_size,
+    uint64_t bos_tok,
+    uint64_t eos_tok)
+    : Tokenizer(vocab_size, bos_tok, eos_tok),
+      vocab_(std::make_unique<char*[]>(vocab_size)),
+      vocab_scores_(std::make_unique<float[]>(vocab_size)),
+      sorted_vocab_(std::make_unique<TokenIndex[]>(vocab_size)) {
+  for (int i = 0; i < 256; i++) {
+    byte_pieces_[i * 2] = (unsigned char)i;
+    byte_pieces_[i * 2 + 1] = '\0';
+  }
+}
+
+/**
+ * @brief Load the tokenizer from a file. The tokenizer file contains the
+ * vocabulary and scores. The format is: the first integer is the maximum
+ * token length, followed by a list of (word_len, word) pairs. Here we
+ * are reading all the vocabulary into memory and keep it sorted for fast
+ * lookup.
+ *
+ * @param tokenizer_path The path to the tokenizer file.
+ * @return void
+ */
+void BPETokenizer::load(const std::string& tokenizer_path) {
+  if (initialized_) {
+    fprintf(stderr, "Tokenizer already initialized.");
+    return;
+  }
+  // read in the file
+  FILE* file = fopen(tokenizer_path.c_str(), "rb");
+  if (!file) {
+    fprintf(stderr, "couldn't load %s", tokenizer_path.c_str());
+    exit(EXIT_FAILURE);
+  }
+  int32_t metadata[2];
+  for (int i = 0; i < 2; i++) {
+    if (fread(metadata + i, sizeof(int32_t), 1, file) != 1) {
+      fprintf(
+          stderr,
+          "Failed to read the metadata at position %d, the tokenizer file is not valid!",
+          i);
+      exit(EXIT_FAILURE);
+    }
+  }
+
+  // now we have two vocab_sizes one from the model and another from the
+  // tokenizer file.
+  int32_t tokenizer_vocab_size = metadata[0];
+  if (tokenizer_vocab_size < vocab_size_) {
+    fprintf(
+        stderr,
+        "The tokenizer vocab size %d is smaller than the model vocab size %d, will add padding tokens.",
+        tokenizer_vocab_size,
+        vocab_size_);
+  } else if (tokenizer_vocab_size > vocab_size_) {
+    fprintf(
+        stderr,
+        "The tokenizer vocab size %d is larger than the model vocab size %d.",
+        tokenizer_vocab_size,
+        vocab_size_);
+  }
+
+  max_token_length_ = metadata[1];
+
+  // allocate space for the vocabulary
+  vocab_ = std::make_unique<char*[]>(vocab_size_);
+  vocab_scores_ = std::make_unique<float[]>(vocab_size_);
+  sorted_vocab_ = std::make_unique<TokenIndex[]>(vocab_size_);
+
+  // read in the vocabulary
+  for (int i = 0; i < vocab_size_; i++) {
+    if (fread(vocab_scores_.get() + i, sizeof(float), 1, file) != 1) {
+      // This is allowed, we just pad the rest of the vocab with <pad> strings
+      std::string padding = "<pad>";
+      vocab_[i] = new char[padding.length() + 1];
+      strcpy(vocab_[i], padding.c_str());
+      vocab_[i][padding.length()] = '\0';
+      continue;
+    }
+    int32_t len;
+    if (fread(&len, sizeof(int32_t), 1, file) != 1) {
+      fprintf(stderr, "Failed to read the length of the word at index %d", i);
+      exit(EXIT_FAILURE);
+    }
+    vocab_[i] = new char[len + 1];
+    if (fread(vocab_[i], len, 1, file) != 1) {
+      fprintf(
+          stderr,
+          "Failed to read the word, total length %d, index %d\n",
+          len,
+          i);
+      exit(EXIT_FAILURE);
+    }
+    vocab_[i][len] = '\0'; // add the string terminating token
+  }
+  fclose(file);
+
+  for (int32_t i = 0; i < vocab_size_; i++) {
+    sorted_vocab_[i].str = vocab_[i];
+    sorted_vocab_[i].id = i;
+  }
+  qsort(sorted_vocab_.get(), vocab_size_, sizeof(TokenIndex), compare_tokens);
+
+  initialized_ = true;
+}
+
+BPETokenizer::~BPETokenizer() {
+  for (int i = 0; i < vocab_size_; i++) {
+    delete[] vocab_[i];
+  }
+}
+
+/**
+ * @brief Decode a token into string.
+ *
+ * @param prev_token The previous token.
+ * @param token The current token.
+ * @return std::string A pointer to the string representation of the
+ * token.
+ */
+std::string BPETokenizer::decode(uint64_t prev_token, uint64_t token) {
+  if (!initialized_) {
+    fprintf(stderr, "Tokenizer not initialized");
+    exit(EXIT_FAILURE);
+  }
+  const char* piece = vocab_[token];
+  // following BOS token, sentencepiece decoder strips any leading
+  // whitespace
+  if (prev_token == bos_tok_ && piece[0] == ' ') {
+    piece++;
+  }
+  // careful, some tokens designate raw bytes, and look like e.g. '<0x01>'
+  // parse this and convert and return the actual byte
+  unsigned char byte_val;
+  if (sscanf(piece, "<0x%02hhX>", &byte_val) == 1) {
+    piece = (char*)byte_pieces_ + byte_val * 2;
+  }
+  std::string res(piece);
+  return res;
+}
+
+static int32_t
+str_lookup(const char* str, TokenIndex* sorted_vocab, int32_t vocab_size) {
+  // efficiently find the perfect match for str in vocab, return its index or -1
+  // if not found
+  TokenIndex tok = {.str = str}; // acts as the key to search for
+  TokenIndex* res = (TokenIndex*)bsearch(
+      &tok, sorted_vocab, vocab_size, sizeof(TokenIndex), compare_tokens);
+  return res != nullptr ? res->id : -1;
+}
+
+/**
+ * @brief Encode a string into a sequence of tokens.
+ *
+ * @param text The string to be encoded.
+ * @param bos The number of BOS to prepend to the token list.
+ * @param eos The number of EOS to append to the token list.
+ * @param tokens The output tokens.
+ * @param n_tokens The number of tokens.
+ * @return std::vector<uint64_t>
+ */
+std::vector<uint64_t>
+BPETokenizer::encode(const std::string& text, int8_t bos, int8_t eos) {
+  if (!initialized_) {
+    fprintf(stderr, "Tokenizer not initialized");
+    exit(EXIT_FAILURE);
+  }
+  // encode the string text (input) into an upper-bound preallocated tokens[]
+  // array bos != 0 means prepend the BOS token (=1), eos != 0 means append the
+  // EOS token (=2)
+  if (text.empty()) {
+    fprintf(stderr, "cannot encode empty text");
+    exit(EXIT_FAILURE);
+  }
+
+  // create a temporary buffer that will store merge candidates of always two
+  // consecutive tokens *2 for concat, +1 for null terminator +2 for UTF8 (in
+  // case max_token_length is 1)
+  char* str_buffer = new char[max_token_length_ * 2 + 1 + 2];
+  size_t str_len = 0;
+
+  // start at 0 tokens
+  std::vector<uint64_t> tokens;
+
+  // add optional BOS token, if desired
+  if (bos > 0) {
+    while (bos--) {
+      tokens.push_back(bos_tok_);
+    }
+  } else {
+    fprintf(stderr, "bos %d should be >= 0", bos);
+    exit(EXIT_FAILURE);
+  }
+
+  // add_dummy_prefix is true by default
+  // so prepend a dummy prefix token to the input string, but only if text != ""
+  // TODO: pretty sure this isn't correct in the general case but I don't have
+  // the energy to read more of the sentencepiece code to figure out what it's
+  // doing
+  const char* space = " ";
+  if (text[0] != '\0') {
+    int dummy_prefix = str_lookup(space, sorted_vocab_.get(), vocab_size_);
+    tokens.push_back(dummy_prefix);
+  }
+
+  // Okay UTF-8 time. This will get messy. Here is the reference from Uncyclopedia:
+  // Code point ↔ UTF-8 conversion
+  // First code point	Last code point	Byte 1	Byte 2	Byte 3	Byte 4
+  // U+0000	U+007F	    0xxxxxxx
+  // U+0080	U+07FF	    110xxxxx	10xxxxxx
+  // U+0800	U+FFFF	    1110xxxx	10xxxxxx	10xxxxxx
+  // U+10000	U+10FFFF    11110xxx	10xxxxxx	10xxxxxx	10xxxxxx
+
+  // process the raw (UTF-8) byte sequence of the input string
+  for (const char* c = text.c_str(); *c != '\0'; c++) {
+    // reset buffer if the current byte is ASCII or a leading byte
+    // 0xC0 is 11000000, so (*c & 0xC0) keeps the first 2 bits and zeros the
+    // rest 0x80 is 10000000 in UTF-8, all continuation bytes start with "10" in
+    // first two bits so in English this is: "if this byte is not a continuation
+    // byte"
+    if ((*c & 0xC0) != 0x80) {
+      // this byte must be either a leading byte (11...) or an ASCII char
+      // (0x...)
+      // => reset our location, as we're starting a new UTF-8 codepoint
+      str_len = 0;
+    }
+
+    // append the current byte to the buffer
+    str_buffer[str_len++] =
+        *c; // ++ is post-increment, incremented after this line
+    str_buffer[str_len] = '\0';
+
+    // while the next character is a continuation byte, continue appending
+    // but if there are too many of them, just stop to avoid overruning
+    // str_buffer size.
+    if ((*(c + 1) & 0xC0) == 0x80 && str_len < 4) {
+      continue;
+    }
+
+    // ok c+1 is not a continuation byte, so we've read in a full codepoint
+    int id = str_lookup(str_buffer, sorted_vocab_.get(), vocab_size_);
+    if (id != -1) {
+      // we found this codepoint in vocab, add it as a token
+      tokens.push_back(id);
+    } else {
+      // byte_fallback encoding: just encode each byte as a token
+      // +3 is here because the first 3 vocab elements are <unk>, <s>, </s>
+      // so the individual bytes only start at index 3
+      for (int i = 0; i < str_len; i++) {
+        tokens.push_back((unsigned char)str_buffer[i] + 3);
+      }
+    }
+    str_len = 0; // protect against a sequence of stray UTF8 continuation bytes
+  }
+
+  // merge the best consecutive pair each iteration, according the scores in
+  // vocab_scores
+  while (1) {
+    float best_score = -1e10;
+    int best_id = -1;
+    int best_idx = -1;
+
+    for (int i = 0; i < tokens.size() - 1; i++) {
+      // check if we can merge the pair (tokens[i], tokens[i+1])
+      snprintf(
+          str_buffer,
+          max_token_length_ * 2 + 3,
+          "%s%s",
+          vocab_[tokens[i]],
+          vocab_[tokens[i + 1]]);
+      int id = str_lookup(str_buffer, sorted_vocab_.get(), vocab_size_);
+      if (id != -1 && vocab_scores_[id] > best_score) {
+        // this merge pair exists in vocab! record its score and position
+        best_score = vocab_scores_[id];
+        best_id = id;
+        best_idx = i;
+      }
+    }
+
+    if (best_idx == -1) {
+      break; // we couldn't find any more pairs to merge, so we're done
+    }
+
+    // merge the consecutive pair (best_idx, best_idx+1) into new token best_id
+    tokens[best_idx] = best_id;
+    // delete token at position best_idx+1, shift the entire sequence back 1
+    for (int i = best_idx + 1; i < tokens.size() - 1; i++) {
+      tokens[i] = tokens[i + 1];
+    }
+    tokens.pop_back(); // token length decreased
+  }
+
+  // add optional EOS (=2) token, if desired
+  if (eos >= 0) {
+    while (eos--) {
+      tokens.push_back(eos_tok_);
+    }
+  } else {
+    fprintf(stderr, "eos %d should be >= 0", eos);
+    exit(EXIT_FAILURE);
+  }
+
+  delete[] str_buffer;
+  return tokens;
+}