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LatinIME/native/src/binary_format.h

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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef LATINIME_BINARY_FORMAT_H
#define LATINIME_BINARY_FORMAT_H
#include "unigram_dictionary.h"
namespace latinime {
class BinaryFormat {
private:
const static int32_t MINIMAL_ONE_BYTE_CHARACTER_VALUE = 0x20;
const static int32_t CHARACTER_ARRAY_TERMINATOR = 0x1F;
const static int MULTIPLE_BYTE_CHARACTER_ADDITIONAL_SIZE = 2;
public:
const static int UNKNOWN_FORMAT = -1;
const static int FORMAT_VERSION_1 = 1;
const static uint16_t FORMAT_VERSION_1_MAGIC_NUMBER = 0x78B1;
static int detectFormat(const uint8_t* const dict);
static int getGroupCountAndForwardPointer(const uint8_t* const dict, int* pos);
static uint8_t getFlagsAndForwardPointer(const uint8_t* const dict, int* pos);
static int32_t getCharCodeAndForwardPointer(const uint8_t* const dict, int* pos);
static int readFrequencyWithoutMovingPointer(const uint8_t* const dict, const int pos);
static int skipOtherCharacters(const uint8_t* const dict, const int pos);
static int skipAttributes(const uint8_t* const dict, const int pos);
static int skipChildrenPosition(const uint8_t flags, const int pos);
static int skipFrequency(const uint8_t flags, const int pos);
static int skipAllAttributes(const uint8_t* const dict, const uint8_t flags, const int pos);
static int skipChildrenPosAndAttributes(const uint8_t* const dict, const uint8_t flags,
const int pos);
static int readChildrenPosition(const uint8_t* const dict, const uint8_t flags, const int pos);
static bool hasChildrenInFlags(const uint8_t flags);
static int getAttributeAddressAndForwardPointer(const uint8_t* const dict, const uint8_t flags,
int *pos);
static int getTerminalPosition(const uint8_t* const root, const uint16_t* const inWord,
const int length);
static int getWordAtAddress(const uint8_t* const root, const int address, const int maxDepth,
uint16_t* outWord);
};
inline int BinaryFormat::detectFormat(const uint8_t* const dict) {
const uint16_t magicNumber = (dict[0] << 8) + dict[1]; // big endian
if (FORMAT_VERSION_1_MAGIC_NUMBER == magicNumber) return FORMAT_VERSION_1;
return UNKNOWN_FORMAT;
}
inline int BinaryFormat::getGroupCountAndForwardPointer(const uint8_t* const dict, int* pos) {
const int msb = dict[(*pos)++];
if (msb < 0x80) return msb;
return ((msb & 0x7F) << 8) | dict[(*pos)++];
}
inline uint8_t BinaryFormat::getFlagsAndForwardPointer(const uint8_t* const dict, int* pos) {
return dict[(*pos)++];
}
inline int32_t BinaryFormat::getCharCodeAndForwardPointer(const uint8_t* const dict, int* pos) {
const int origin = *pos;
const int32_t character = dict[origin];
if (character < MINIMAL_ONE_BYTE_CHARACTER_VALUE) {
if (character == CHARACTER_ARRAY_TERMINATOR) {
*pos = origin + 1;
return NOT_A_CHARACTER;
} else {
*pos = origin + 3;
const int32_t char_1 = character << 16;
const int32_t char_2 = char_1 + (dict[origin + 1] << 8);
return char_2 + dict[origin + 2];
}
} else {
*pos = origin + 1;
return character;
}
}
inline int BinaryFormat::readFrequencyWithoutMovingPointer(const uint8_t* const dict,
const int pos) {
return dict[pos];
}
inline int BinaryFormat::skipOtherCharacters(const uint8_t* const dict, const int pos) {
int currentPos = pos;
int32_t character = dict[currentPos++];
while (CHARACTER_ARRAY_TERMINATOR != character) {
if (character < MINIMAL_ONE_BYTE_CHARACTER_VALUE) {
currentPos += MULTIPLE_BYTE_CHARACTER_ADDITIONAL_SIZE;
}
character = dict[currentPos++];
}
return currentPos;
}
static inline int attributeAddressSize(const uint8_t flags) {
static const int ATTRIBUTE_ADDRESS_SHIFT = 4;
return (flags & UnigramDictionary::MASK_ATTRIBUTE_ADDRESS_TYPE) >> ATTRIBUTE_ADDRESS_SHIFT;
/* Note: this is a value-dependant optimization of what may probably be
more readably written this way:
switch (flags * UnigramDictionary::MASK_ATTRIBUTE_ADDRESS_TYPE) {
case UnigramDictionary::FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE: return 1;
case UnigramDictionary::FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES: return 2;
case UnigramDictionary::FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTE: return 3;
default: return 0;
}
*/
}
inline int BinaryFormat::skipAttributes(const uint8_t* const dict, const int pos) {
int currentPos = pos;
uint8_t flags = getFlagsAndForwardPointer(dict, &currentPos);
while (flags & UnigramDictionary::FLAG_ATTRIBUTE_HAS_NEXT) {
currentPos += attributeAddressSize(flags);
flags = getFlagsAndForwardPointer(dict, &currentPos);
}
currentPos += attributeAddressSize(flags);
return currentPos;
}
static inline int childrenAddressSize(const uint8_t flags) {
static const int CHILDREN_ADDRESS_SHIFT = 6;
return (UnigramDictionary::MASK_GROUP_ADDRESS_TYPE & flags) >> CHILDREN_ADDRESS_SHIFT;
/* See the note in attributeAddressSize. The same applies here */
}
inline int BinaryFormat::skipChildrenPosition(const uint8_t flags, const int pos) {
return pos + childrenAddressSize(flags);
}
inline int BinaryFormat::skipFrequency(const uint8_t flags, const int pos) {
return UnigramDictionary::FLAG_IS_TERMINAL & flags ? pos + 1 : pos;
}
inline int BinaryFormat::skipAllAttributes(const uint8_t* const dict, const uint8_t flags,
const int pos) {
// This function skips all attributes: shortcuts and bigrams.
int newPos = pos;
if (UnigramDictionary::FLAG_HAS_SHORTCUT_TARGETS & flags) {
newPos = skipAttributes(dict, newPos);
}
if (UnigramDictionary::FLAG_HAS_BIGRAMS & flags) {
newPos = skipAttributes(dict, newPos);
}
return newPos;
}
inline int BinaryFormat::skipChildrenPosAndAttributes(const uint8_t* const dict,
const uint8_t flags, const int pos) {
int currentPos = pos;
currentPos = skipChildrenPosition(flags, currentPos);
currentPos = skipAllAttributes(dict, flags, currentPos);
return currentPos;
}
inline int BinaryFormat::readChildrenPosition(const uint8_t* const dict, const uint8_t flags,
const int pos) {
int offset = 0;
switch (UnigramDictionary::MASK_GROUP_ADDRESS_TYPE & flags) {
case UnigramDictionary::FLAG_GROUP_ADDRESS_TYPE_ONEBYTE:
offset = dict[pos];
break;
case UnigramDictionary::FLAG_GROUP_ADDRESS_TYPE_TWOBYTES:
offset = dict[pos] << 8;
offset += dict[pos + 1];
break;
case UnigramDictionary::FLAG_GROUP_ADDRESS_TYPE_THREEBYTES:
offset = dict[pos] << 16;
offset += dict[pos + 1] << 8;
offset += dict[pos + 2];
break;
default:
// If we come here, it means we asked for the children of a word with
// no children.
return -1;
}
return pos + offset;
}
inline bool BinaryFormat::hasChildrenInFlags(const uint8_t flags) {
return (UnigramDictionary::FLAG_GROUP_ADDRESS_TYPE_NOADDRESS
!= (UnigramDictionary::MASK_GROUP_ADDRESS_TYPE & flags));
}
inline int BinaryFormat::getAttributeAddressAndForwardPointer(const uint8_t* const dict,
const uint8_t flags, int *pos) {
int offset = 0;
const int origin = *pos;
switch (UnigramDictionary::MASK_ATTRIBUTE_ADDRESS_TYPE & flags) {
case UnigramDictionary::FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE:
offset = dict[origin];
*pos = origin + 1;
break;
case UnigramDictionary::FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES:
offset = dict[origin] << 8;
offset += dict[origin + 1];
*pos = origin + 2;
break;
case UnigramDictionary::FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES:
offset = dict[origin] << 16;
offset += dict[origin + 1] << 8;
offset += dict[origin + 2];
*pos = origin + 3;
break;
}
if (UnigramDictionary::FLAG_ATTRIBUTE_OFFSET_NEGATIVE & flags) {
return origin - offset;
} else {
return origin + offset;
}
}
// This function gets the byte position of the last chargroup of the exact matching word in the
// dictionary. If no match is found, it returns NOT_VALID_WORD.
inline int BinaryFormat::getTerminalPosition(const uint8_t* const root,
const uint16_t* const inWord, const int length) {
int pos = 0;
int wordPos = 0;
while (true) {
// If we already traversed the tree further than the word is long, there means
// there was no match (or we would have found it).
if (wordPos > length) return NOT_VALID_WORD;
int charGroupCount = BinaryFormat::getGroupCountAndForwardPointer(root, &pos);
const uint16_t wChar = inWord[wordPos];
while (true) {
// If there are no more character groups in this node, it means we could not
// find a matching character for this depth, therefore there is no match.
if (0 >= charGroupCount) return NOT_VALID_WORD;
const int charGroupPos = pos;
const uint8_t flags = BinaryFormat::getFlagsAndForwardPointer(root, &pos);
int32_t character = BinaryFormat::getCharCodeAndForwardPointer(root, &pos);
if (character == wChar) {
// This is the correct node. Only one character group may start with the same
// char within a node, so either we found our match in this node, or there is
// no match and we can return NOT_VALID_WORD. So we will check all the characters
// in this character group indeed does match.
if (UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS & flags) {
character = BinaryFormat::getCharCodeAndForwardPointer(root, &pos);
while (NOT_A_CHARACTER != character) {
++wordPos;
// If we shoot the length of the word we search for, or if we find a single
// character that does not match, as explained above, it means the word is
// not in the dictionary (by virtue of this chargroup being the only one to
// match the word on the first character, but not matching the whole word).
if (wordPos > length) return NOT_VALID_WORD;
if (inWord[wordPos] != character) return NOT_VALID_WORD;
character = BinaryFormat::getCharCodeAndForwardPointer(root, &pos);
}
}
// If we come here we know that so far, we do match. Either we are on a terminal
// and we match the length, in which case we found it, or we traverse children.
// If we don't match the length AND don't have children, then a word in the
// dictionary fully matches a prefix of the searched word but not the full word.
++wordPos;
if (UnigramDictionary::FLAG_IS_TERMINAL & flags) {
if (wordPos == length) {
return charGroupPos;
}
pos = BinaryFormat::skipFrequency(UnigramDictionary::FLAG_IS_TERMINAL, pos);
}
if (UnigramDictionary::FLAG_GROUP_ADDRESS_TYPE_NOADDRESS
== (UnigramDictionary::MASK_GROUP_ADDRESS_TYPE & flags)) {
return NOT_VALID_WORD;
}
// We have children and we are still shorter than the word we are searching for, so
// we need to traverse children. Put the pointer on the children position, and
// break
pos = BinaryFormat::readChildrenPosition(root, flags, pos);
break;
} else {
// This chargroup does not match, so skip the remaining part and go to the next.
if (UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS & flags) {
pos = BinaryFormat::skipOtherCharacters(root, pos);
}
pos = BinaryFormat::skipFrequency(flags, pos);
pos = BinaryFormat::skipChildrenPosAndAttributes(root, flags, pos);
}
--charGroupCount;
}
}
}
// This function searches for a terminal in the dictionary by its address.
// Due to the fact that words are ordered in the dictionary in a strict breadth-first order,
// it is possible to check for this with advantageous complexity. For each node, we search
// for groups with children and compare the children address with the address we look for.
// When we shoot the address we look for, it means the word we look for is in the children
// of the previous group. The only tricky part is the fact that if we arrive at the end of a
// node with the last group's children address still less than what we are searching for, we
// must descend the last group's children (for example, if the word we are searching for starts
// with a z, it's the last group of the root node, so all children addresses will be smaller
// than the address we look for, and we have to descend the z node).
/* Parameters :
* root: the dictionary buffer
* address: the byte position of the last chargroup of the word we are searching for (this is
* what is stored as the "bigram address" in each bigram)
* outword: an array to write the found word, with MAX_WORD_LENGTH size.
* Return value : the length of the word, of 0 if the word was not found.
*/
inline int BinaryFormat::getWordAtAddress(const uint8_t* const root, const int address,
const int maxDepth, uint16_t* outWord) {
int pos = 0;
int wordPos = 0;
// One iteration of the outer loop iterates through nodes. As stated above, we will only
// traverse nodes that are actually a part of the terminal we are searching, so each time
// we enter this loop we are one depth level further than last time.
// The only reason we count nodes is because we want to reduce the probability of infinite
// looping in case there is a bug. Since we know there is an upper bound to the depth we are
// supposed to traverse, it does not hurt to count iterations.
for (int loopCount = maxDepth; loopCount > 0; --loopCount) {
int lastCandidateGroupPos = 0;
// Let's loop through char groups in this node searching for either the terminal
// or one of its ascendants.
for (int charGroupCount = getGroupCountAndForwardPointer(root, &pos); charGroupCount > 0;
--charGroupCount) {
const int startPos = pos;
const uint8_t flags = getFlagsAndForwardPointer(root, &pos);
const int32_t character = getCharCodeAndForwardPointer(root, &pos);
if (address == startPos) {
// We found the address. Copy the rest of the word in the buffer and return
// the length.
outWord[wordPos] = character;
if (UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS & flags) {
int32_t nextChar = getCharCodeAndForwardPointer(root, &pos);
// We count chars in order to avoid infinite loops if the file is broken or
// if there is some other bug
int charCount = maxDepth;
while (-1 != nextChar && --charCount > 0) {
outWord[++wordPos] = nextChar;
nextChar = getCharCodeAndForwardPointer(root, &pos);
}
}
return ++wordPos;
}
// We need to skip past this char group, so skip any remaining chars after the
// first and possibly the frequency.
if (UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS & flags) {
pos = skipOtherCharacters(root, pos);
}
pos = skipFrequency(flags, pos);
// The fact that this group has children is very important. Since we already know
// that this group does not match, if it has no children we know it is irrelevant
// to what we are searching for.
const bool hasChildren = (UnigramDictionary::FLAG_GROUP_ADDRESS_TYPE_NOADDRESS !=
(UnigramDictionary::MASK_GROUP_ADDRESS_TYPE & flags));
// We will write in `found' whether we have passed the children address we are
// searching for. For example if we search for "beer", the children of b are less
// than the address we are searching for and the children of c are greater. When we
// come here for c, we realize this is too big, and that we should descend b.
bool found;
if (hasChildren) {
// Here comes the tricky part. First, read the children position.
const int childrenPos = readChildrenPosition(root, flags, pos);
if (childrenPos > address) {
// If the children pos is greater than address, it means the previous chargroup,
// which address is stored in lastCandidateGroupPos, was the right one.
found = true;
} else if (1 >= charGroupCount) {
// However if we are on the LAST group of this node, and we have NOT shot the
// address we should descend THIS node. So we trick the lastCandidateGroupPos
// so that we will descend this node, not the previous one.
lastCandidateGroupPos = startPos;
found = true;
} else {
// Else, we should continue looking.
found = false;
}
} else {
// Even if we don't have children here, we could still be on the last group of this
// node. If this is the case, we should descend the last group that had children,
// and their address is already in lastCandidateGroup.
found = (1 >= charGroupCount);
}
if (found) {
// Okay, we found the group we should descend. Its address is in
// the lastCandidateGroupPos variable, so we just re-read it.
if (0 != lastCandidateGroupPos) {
const uint8_t lastFlags =
getFlagsAndForwardPointer(root, &lastCandidateGroupPos);
const int32_t lastChar =
getCharCodeAndForwardPointer(root, &lastCandidateGroupPos);
// We copy all the characters in this group to the buffer
outWord[wordPos] = lastChar;
if (UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS & lastFlags) {
int32_t nextChar =
getCharCodeAndForwardPointer(root, &lastCandidateGroupPos);
int charCount = maxDepth;
while (-1 != nextChar && --charCount > 0) {
outWord[++wordPos] = nextChar;
nextChar = getCharCodeAndForwardPointer(root, &lastCandidateGroupPos);
}
}
++wordPos;
// Now we only need to branch to the children address. Skip the frequency if
// it's there, read pos, and break to resume the search at pos.
lastCandidateGroupPos = skipFrequency(lastFlags, lastCandidateGroupPos);
pos = readChildrenPosition(root, lastFlags, lastCandidateGroupPos);
break;
} else {
// Here is a little tricky part: we come here if we found out that all children
// addresses in this group are bigger than the address we are searching for.
// Should we conclude the word is not in the dictionary? No! It could still be
// one of the remaining chargroups in this node, so we have to keep looking in
// this node until we find it (or we realize it's not there either, in which
// case it's actually not in the dictionary). Pass the end of this group, ready
// to start the next one.
pos = skipChildrenPosAndAttributes(root, flags, pos);
}
} else {
// If we did not find it, we should record the last children address for the next
// iteration.
if (hasChildren) lastCandidateGroupPos = startPos;
// Now skip the end of this group (children pos and the attributes if any) so that
// our pos is after the end of this char group, at the start of the next one.
pos = skipChildrenPosAndAttributes(root, flags, pos);
}
}
}
// If we have looked through all the chargroups and found no match, the address is
// not the address of a terminal in this dictionary.
return 0;
}
} // namespace latinime
#endif // LATINIME_BINARY_FORMAT_H
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