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 // © 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) |
             (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 (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__

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