tor-browser

bytestrie.h (21327B)

---

// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
*******************************************************************************
*   Copyright (C) 2010-2012, International Business Machines
*   Corporation and others.  All Rights Reserved.
*******************************************************************************
*   file name:  bytestrie.h
*   encoding:   UTF-8
*   tab size:   8 (not used)
*   indentation:4
*
*   created on: 2010sep25
*   created by: Markus W. Scherer
*/

#ifndef __BYTESTRIE_H__
#define __BYTESTRIE_H__

/**
* \file
* \brief C++ API: Trie for mapping byte sequences to integer values.
*/

#include "unicode/utypes.h"

#if U_SHOW_CPLUSPLUS_API

#include "unicode/stringpiece.h"
#include "unicode/uobject.h"
#include "unicode/ustringtrie.h"

class BytesTrieTest;

U_NAMESPACE_BEGIN

class ByteSink;
class BytesTrieBuilder;
class CharString;
class UVector32;

/**
* Light-weight, non-const reader class for a BytesTrie.
* Traverses a byte-serialized data structure with minimal state,
* for mapping byte sequences to non-negative integer values.
*
* This class owns the serialized trie data only if it was constructed by
* the builder's build() method.
* The public constructor and the copy constructor only alias the data (only copy the pointer).
* There is no assignment operator.
*
* This class is not intended for public subclassing.
* @stable ICU 4.8
*/
class U_COMMON_API BytesTrie : public UMemory {
public:
   /**
    * Constructs a BytesTrie reader instance.
    *
    * The trieBytes must contain a copy of a byte sequence from the BytesTrieBuilder,
    * starting with the first byte of that sequence.
    * The BytesTrie object will not read more bytes than
    * the BytesTrieBuilder generated in the corresponding build() call.
    *
    * The array is not copied/cloned and must not be modified while
    * the BytesTrie object is in use.
    *
    * @param trieBytes The byte array that contains the serialized trie.
    * @stable ICU 4.8
    */
   BytesTrie(const void *trieBytes)
           : ownedArray_(nullptr), bytes_(static_cast<const uint8_t *>(trieBytes)),
             pos_(bytes_), remainingMatchLength_(-1) {}

   /**
    * Destructor.
    * @stable ICU 4.8
    */
   ~BytesTrie();

   /**
    * Copy constructor, copies the other trie reader object and its state,
    * but not the byte array which will be shared. (Shallow copy.)
    * @param other Another BytesTrie object.
    * @stable ICU 4.8
    */
   BytesTrie(const BytesTrie &other)
           : ownedArray_(nullptr), bytes_(other.bytes_),
             pos_(other.pos_), remainingMatchLength_(other.remainingMatchLength_) {}

   /**
    * Resets this trie to its initial state.
    * @return *this
    * @stable ICU 4.8
    */
   BytesTrie &reset() {
       pos_=bytes_;
       remainingMatchLength_=-1;
       return *this;
   }

   /**
    * Returns the state of this trie as a 64-bit integer.
    * The state value is never 0.
    *
    * @return opaque state value
    * @see resetToState64
    * @stable ICU 65
    */
   uint64_t getState64() const {
       return (static_cast<uint64_t>(remainingMatchLength_ + 2) << kState64RemainingShift) |
           static_cast<uint64_t>(pos_ - bytes_);
   }

   /**
    * Resets this trie to the saved state.
    * Unlike resetToState(State), the 64-bit state value
    * must be from getState64() from the same trie object or
    * from one initialized the exact same way.
    * Because of no validation, this method is faster.
    *
    * @param state The opaque trie state value from getState64().
    * @return *this
    * @see getState64
    * @see resetToState
    * @see reset
    * @stable ICU 65
    */
   BytesTrie &resetToState64(uint64_t state) {
       remainingMatchLength_ = static_cast<int32_t>(state >> kState64RemainingShift) - 2;
       pos_ = bytes_ + (state & kState64PosMask);
       return *this;
   }

   /**
    * BytesTrie state object, for saving a trie's current state
    * and resetting the trie back to this state later.
    * @stable ICU 4.8
    */
   class State : public UMemory {
   public:
       /**
        * Constructs an empty State.
        * @stable ICU 4.8
        */
       State() { bytes=nullptr; }
   private:
       friend class BytesTrie;

       const uint8_t *bytes;
       const uint8_t *pos;
       int32_t remainingMatchLength;
   };

   /**
    * Saves the state of this trie.
    * @param state The State object to hold the trie's state.
    * @return *this
    * @see resetToState
    * @stable ICU 4.8
    */
   const BytesTrie &saveState(State &state) const {
       state.bytes=bytes_;
       state.pos=pos_;
       state.remainingMatchLength=remainingMatchLength_;
       return *this;
   }

   /**
    * Resets this trie to the saved state.
    * If the state object contains no state, or the state of a different trie,
    * then this trie remains unchanged.
    * @param state The State object which holds a saved trie state.
    * @return *this
    * @see saveState
    * @see reset
    * @stable ICU 4.8
    */
   BytesTrie &resetToState(const State &state) {
       if(bytes_==state.bytes && bytes_!=nullptr) {
           pos_=state.pos;
           remainingMatchLength_=state.remainingMatchLength;
       }
       return *this;
   }

   /**
    * Determines whether the byte sequence so far matches, whether it has a value,
    * and whether another input byte can continue a matching byte sequence.
    * @return The match/value Result.
    * @stable ICU 4.8
    */
   UStringTrieResult current() const;

   /**
    * Traverses the trie from the initial state for this input byte.
    * Equivalent to reset().next(inByte).
    * @param inByte Input byte value. Values -0x100..-1 are treated like 0..0xff.
    *               Values below -0x100 and above 0xff will never match.
    * @return The match/value Result.
    * @stable ICU 4.8
    */
   inline UStringTrieResult first(int32_t inByte) {
       remainingMatchLength_=-1;
       if(inByte<0) {
           inByte+=0x100;
       }
       return nextImpl(bytes_, inByte);
   }

   /**
    * Traverses the trie from the current state for this input byte.
    * @param inByte Input byte value. Values -0x100..-1 are treated like 0..0xff.
    *               Values below -0x100 and above 0xff will never match.
    * @return The match/value Result.
    * @stable ICU 4.8
    */
   UStringTrieResult next(int32_t inByte);

   /**
    * Traverses the trie from the current state for this byte sequence.
    * Equivalent to
    * \code
    * Result result=current();
    * for(each c in s)
    *   if(!USTRINGTRIE_HAS_NEXT(result)) return USTRINGTRIE_NO_MATCH;
    *   result=next(c);
    * return result;
    * \endcode
    * @param s A string or byte sequence. Can be nullptr if length is 0.
    * @param length The length of the byte sequence. Can be -1 if NUL-terminated.
    * @return The match/value Result.
    * @stable ICU 4.8
    */
   UStringTrieResult next(const char *s, int32_t length);

   /**
    * Returns a matching byte sequence's value if called immediately after
    * current()/first()/next() returned USTRINGTRIE_INTERMEDIATE_VALUE or USTRINGTRIE_FINAL_VALUE.
    * getValue() can be called multiple times.
    *
    * Do not call getValue() after USTRINGTRIE_NO_MATCH or USTRINGTRIE_NO_VALUE!
    * @return The value for the byte sequence so far.
    * @stable ICU 4.8
    */
   inline int32_t getValue() const {
       const uint8_t *pos=pos_;
       int32_t leadByte=*pos++;
       // U_ASSERT(leadByte>=kMinValueLead);
       return readValue(pos, leadByte>>1);
   }

   /**
    * Determines whether all byte sequences reachable from the current state
    * map to the same value.
    * @param uniqueValue Receives the unique value, if this function returns true.
    *                    (output-only)
    * @return true if all byte sequences reachable from the current state
    *         map to the same value.
    * @stable ICU 4.8
    */
   inline UBool hasUniqueValue(int32_t &uniqueValue) const {
       const uint8_t *pos=pos_;
       // Skip the rest of a pending linear-match node.
       return pos!=nullptr && findUniqueValue(pos+remainingMatchLength_+1, false, uniqueValue);
   }

   /**
    * Finds each byte which continues the byte sequence from the current state.
    * That is, each byte b for which it would be next(b)!=USTRINGTRIE_NO_MATCH now.
    * @param out Each next byte is appended to this object.
    *            (Only uses the out.Append(s, length) method.)
    * @return the number of bytes which continue the byte sequence from here
    * @stable ICU 4.8
    */
   int32_t getNextBytes(ByteSink &out) const;

   /**
    * Iterator for all of the (byte sequence, value) pairs in a BytesTrie.
    * @stable ICU 4.8
    */
   class U_COMMON_API Iterator : public UMemory {
   public:
       /**
        * Iterates from the root of a byte-serialized BytesTrie.
        * @param trieBytes The trie bytes.
        * @param maxStringLength If 0, the iterator returns full strings/byte sequences.
        *                        Otherwise, the iterator returns strings with this maximum length.
        * @param errorCode Standard ICU error code. Its input value must
        *                  pass the U_SUCCESS() test, or else the function returns
        *                  immediately. Check for U_FAILURE() on output or use with
        *                  function chaining. (See User Guide for details.)
        * @stable ICU 4.8
        */
       Iterator(const void *trieBytes, int32_t maxStringLength, UErrorCode &errorCode);

       /**
        * Iterates from the current state of the specified BytesTrie.
        * @param trie The trie whose state will be copied for iteration.
        * @param maxStringLength If 0, the iterator returns full strings/byte sequences.
        *                        Otherwise, the iterator returns strings with this maximum length.
        * @param errorCode Standard ICU error code. Its input value must
        *                  pass the U_SUCCESS() test, or else the function returns
        *                  immediately. Check for U_FAILURE() on output or use with
        *                  function chaining. (See User Guide for details.)
        * @stable ICU 4.8
        */
       Iterator(const BytesTrie &trie, int32_t maxStringLength, UErrorCode &errorCode);

       /**
        * Destructor.
        * @stable ICU 4.8
        */
       ~Iterator();

       /**
        * Resets this iterator to its initial state.
        * @return *this
        * @stable ICU 4.8
        */
       Iterator &reset();

       /**
        * @return true if there are more elements.
        * @stable ICU 4.8
        */
       UBool hasNext() const;

       /**
        * Finds the next (byte sequence, value) pair if there is one.
        *
        * If the byte sequence is truncated to the maximum length and does not
        * have a real value, then the value is set to -1.
        * In this case, this "not a real value" is indistinguishable from
        * a real value of -1.
        * @param errorCode Standard ICU error code. Its input value must
        *                  pass the U_SUCCESS() test, or else the function returns
        *                  immediately. Check for U_FAILURE() on output or use with
        *                  function chaining. (See User Guide for details.)
        * @return true if there is another element.
        * @stable ICU 4.8
        */
       UBool next(UErrorCode &errorCode);

       /**
        * @return The NUL-terminated byte sequence for the last successful next().
        * @stable ICU 4.8
        */
       StringPiece getString() const;
       /**
        * @return The value for the last successful next().
        * @stable ICU 4.8
        */
       int32_t getValue() const { return value_; }

   private:
       UBool truncateAndStop();

       const uint8_t *branchNext(const uint8_t *pos, int32_t length, UErrorCode &errorCode);

       const uint8_t *bytes_;
       const uint8_t *pos_;
       const uint8_t *initialPos_;
       int32_t remainingMatchLength_;
       int32_t initialRemainingMatchLength_;

       CharString *str_;
       int32_t maxLength_;
       int32_t value_;

       // The stack stores pairs of integers for backtracking to another
       // outbound edge of a branch node.
       // The first integer is an offset from bytes_.
       // The second integer has the str_->length() from before the node in bits 15..0,
       // and the remaining branch length in bits 24..16. (Bits 31..25 are unused.)
       // (We could store the remaining branch length minus 1 in bits 23..16 and not use bits 31..24,
       // but the code looks more confusing that way.)
       UVector32 *stack_;
   };

private:
   friend class BytesTrieBuilder;
   friend class ::BytesTrieTest;

   /**
    * Constructs a BytesTrie reader instance.
    * Unlike the public constructor which just aliases an array,
    * this constructor adopts the builder's array.
    * This constructor is only called by the builder.
    */
   BytesTrie(void *adoptBytes, const void *trieBytes)
           : ownedArray_(static_cast<uint8_t *>(adoptBytes)),
             bytes_(static_cast<const uint8_t *>(trieBytes)),
             pos_(bytes_), remainingMatchLength_(-1) {}

   // No assignment operator.
   BytesTrie &operator=(const BytesTrie &other) = delete;

   inline void stop() {
       pos_=nullptr;
   }

   // Reads a compact 32-bit integer.
   // pos is already after the leadByte, and the lead byte is already shifted right by 1.
   static int32_t readValue(const uint8_t *pos, int32_t leadByte);
   static inline const uint8_t *skipValue(const uint8_t *pos, int32_t leadByte) {
       // U_ASSERT(leadByte>=kMinValueLead);
       if(leadByte>=(kMinTwoByteValueLead<<1)) {
           if(leadByte<(kMinThreeByteValueLead<<1)) {
               ++pos;
           } else if(leadByte<(kFourByteValueLead<<1)) {
               pos+=2;
           } else {
               pos+=3+((leadByte>>1)&1);
           }
       }
       return pos;
   }
   static inline const uint8_t *skipValue(const uint8_t *pos) {
       int32_t leadByte=*pos++;
       return skipValue(pos, leadByte);
   }

   // Reads a jump delta and jumps.
   static const uint8_t *jumpByDelta(const uint8_t *pos);

   static inline const uint8_t *skipDelta(const uint8_t *pos) {
       int32_t delta=*pos++;
       if(delta>=kMinTwoByteDeltaLead) {
           if(delta<kMinThreeByteDeltaLead) {
               ++pos;
           } else if(delta<kFourByteDeltaLead) {
               pos+=2;
           } else {
               pos+=3+(delta&1);
           }
       }
       return pos;
   }

   static inline UStringTrieResult valueResult(int32_t node) {
       return static_cast<UStringTrieResult>(USTRINGTRIE_INTERMEDIATE_VALUE - (node & kValueIsFinal));
   }

   // Handles a branch node for both next(byte) and next(string).
   UStringTrieResult branchNext(const uint8_t *pos, int32_t length, int32_t inByte);

   // Requires remainingLength_<0.
   UStringTrieResult nextImpl(const uint8_t *pos, int32_t inByte);

   // Helper functions for hasUniqueValue().
   // Recursively finds a unique value (or whether there is not a unique one)
   // from a branch.
   static const uint8_t *findUniqueValueFromBranch(const uint8_t *pos, int32_t length,
                                                   UBool haveUniqueValue, int32_t &uniqueValue);
   // Recursively finds a unique value (or whether there is not a unique one)
   // starting from a position on a node lead byte.
   static UBool findUniqueValue(const uint8_t *pos, UBool haveUniqueValue, int32_t &uniqueValue);

   // Helper functions for getNextBytes().
   // getNextBytes() when pos is on a branch node.
   static void getNextBranchBytes(const uint8_t *pos, int32_t length, ByteSink &out);
   static void append(ByteSink &out, int c);

   // BytesTrie data structure
   //
   // The trie consists of a series of byte-serialized nodes for incremental
   // string/byte sequence matching. The root node is at the beginning of the trie data.
   //
   // Types of nodes are distinguished by their node lead byte ranges.
   // After each node, except a final-value node, another node follows to
   // encode match values or continue matching further bytes.
   //
   // Node types:
   //  - Value node: Stores a 32-bit integer in a compact, variable-length format.
   //    The value is for the string/byte sequence so far.
   //    One node bit indicates whether the value is final or whether
   //    matching continues with the next node.
   //  - Linear-match node: Matches a number of bytes.
   //  - Branch node: Branches to other nodes according to the current input byte.
   //    The node byte is the length of the branch (number of bytes to select from)
   //    minus 1. It is followed by a sub-node:
   //    - If the length is at most kMaxBranchLinearSubNodeLength, then
   //      there are length-1 (key, value) pairs and then one more comparison byte.
   //      If one of the key bytes matches, then the value is either a final value for
   //      the string/byte sequence so far, or a "jump" delta to the next node.
   //      If the last byte matches, then matching continues with the next node.
   //      (Values have the same encoding as value nodes.)
   //    - If the length is greater than kMaxBranchLinearSubNodeLength, then
   //      there is one byte and one "jump" delta.
   //      If the input byte is less than the sub-node byte, then "jump" by delta to
   //      the next sub-node which will have a length of length/2.
   //      (The delta has its own compact encoding.)
   //      Otherwise, skip the "jump" delta to the next sub-node
   //      which will have a length of length-length/2.

   // Node lead byte values.

   // 00..0f: Branch node. If node!=0 then the length is node+1, otherwise
   // the length is one more than the next byte.

   // For a branch sub-node with at most this many entries, we drop down
   // to a linear search.
   static const int32_t kMaxBranchLinearSubNodeLength=5;

   // 10..1f: Linear-match node, match 1..16 bytes and continue reading the next node.
   static const int32_t kMinLinearMatch=0x10;
   static const int32_t kMaxLinearMatchLength=0x10;

   // 20..ff: Variable-length value node.
   // If odd, the value is final. (Otherwise, intermediate value or jump delta.)
   // Then shift-right by 1 bit.
   // The remaining lead byte value indicates the number of following bytes (0..4)
   // and contains the value's top bits.
   static const int32_t kMinValueLead=kMinLinearMatch+kMaxLinearMatchLength;  // 0x20
   // It is a final value if bit 0 is set.
   static const int32_t kValueIsFinal=1;

   // Compact value: After testing bit 0, shift right by 1 and then use the following thresholds.
   static const int32_t kMinOneByteValueLead=kMinValueLead/2;  // 0x10
   static const int32_t kMaxOneByteValue=0x40;  // At least 6 bits in the first byte.

   static const int32_t kMinTwoByteValueLead=kMinOneByteValueLead+kMaxOneByteValue+1;  // 0x51
   static const int32_t kMaxTwoByteValue=0x1aff;

   static const int32_t kMinThreeByteValueLead=kMinTwoByteValueLead+(kMaxTwoByteValue>>8)+1;  // 0x6c
   static const int32_t kFourByteValueLead=0x7e;

   // A little more than Unicode code points. (0x11ffff)
   static const int32_t kMaxThreeByteValue=((kFourByteValueLead-kMinThreeByteValueLead)<<16)-1;

   static const int32_t kFiveByteValueLead=0x7f;

   // Compact delta integers.
   static const int32_t kMaxOneByteDelta=0xbf;
   static const int32_t kMinTwoByteDeltaLead=kMaxOneByteDelta+1;  // 0xc0
   static const int32_t kMinThreeByteDeltaLead=0xf0;
   static const int32_t kFourByteDeltaLead=0xfe;
   static const int32_t kFiveByteDeltaLead=0xff;

   static const int32_t kMaxTwoByteDelta=((kMinThreeByteDeltaLead-kMinTwoByteDeltaLead)<<8)-1;  // 0x2fff
   static const int32_t kMaxThreeByteDelta=((kFourByteDeltaLead-kMinThreeByteDeltaLead)<<16)-1;  // 0xdffff

   // For getState64():
   // The remainingMatchLength_ is -1..14=(kMaxLinearMatchLength=0x10)-2
   // so we need at least 5 bits for that.
   // We add 2 to store it as a positive value 1..16=kMaxLinearMatchLength.
   static constexpr int32_t kState64RemainingShift = 59;
   static constexpr uint64_t kState64PosMask = (UINT64_C(1) << kState64RemainingShift) - 1;

   uint8_t *ownedArray_;

   // Fixed value referencing the BytesTrie bytes.
   const uint8_t *bytes_;

   // Iterator variables.

   // Pointer to next trie byte to read. nullptr if no more matches.
   const uint8_t *pos_;
   // Remaining length of a linear-match node, minus 1. Negative if not in such a node.
   int32_t remainingMatchLength_;
};

U_NAMESPACE_END

#endif /* U_SHOW_CPLUSPLUS_API */

#endif  // __BYTESTRIE_H__