com.google.zxing.aztec.encoder.HighLevelEncoder Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of core Show documentation
Show all versions of core Show documentation
Core barcode encoding/decoding library
/*
* Copyright 2013 ZXing authors
*
* 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.
*/
package com.google.zxing.aztec.encoder;
import com.google.zxing.common.BitArray;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
/**
* This produces nearly optimal encodings of text into the first-level of
* encoding used by Aztec code.
*
* It uses a dynamic algorithm. For each prefix of the string, it determines
* a set of encodings that could lead to this prefix. We repeatedly add a
* character and generate a new set of optimal encodings until we have read
* through the entire input.
*
* @author Frank Yellin
* @author Rustam Abdullaev
*/
public final class HighLevelEncoder {
static final String[] MODE_NAMES = {"UPPER", "LOWER", "DIGIT", "MIXED", "PUNCT"};
static final int MODE_UPPER = 0; // 5 bits
static final int MODE_LOWER = 1; // 5 bits
static final int MODE_DIGIT = 2; // 4 bits
static final int MODE_MIXED = 3; // 5 bits
static final int MODE_PUNCT = 4; // 5 bits
// The Latch Table shows, for each pair of Modes, the optimal method for
// getting from one mode to another. In the worst possible case, this can
// be up to 14 bits. In the best possible case, we are already there!
// The high half-word of each entry gives the number of bits.
// The low half-word of each entry are the actual bits necessary to change
static final int[][] LATCH_TABLE = {
{
0,
(5 << 16) + 28, // UPPER -> LOWER
(5 << 16) + 30, // UPPER -> DIGIT
(5 << 16) + 29, // UPPER -> MIXED
(10 << 16) + (29 << 5) + 30, // UPPER -> MIXED -> PUNCT
},
{
(9 << 16) + (30 << 4) + 14, // LOWER -> DIGIT -> UPPER
0,
(5 << 16) + 30, // LOWER -> DIGIT
(5 << 16) + 29, // LOWER -> MIXED
(10 << 16) + (29 << 5) + 30, // LOWER -> MIXED -> PUNCT
},
{
(4 << 16) + 14, // DIGIT -> UPPER
(9 << 16) + (14 << 5) + 28, // DIGIT -> UPPER -> LOWER
0,
(9 << 16) + (14 << 5) + 29, // DIGIT -> UPPER -> MIXED
(14 << 16) + (14 << 10) + (29 << 5) + 30,
// DIGIT -> UPPER -> MIXED -> PUNCT
},
{
(5 << 16) + 29, // MIXED -> UPPER
(5 << 16) + 28, // MIXED -> LOWER
(10 << 16) + (29 << 5) + 30, // MIXED -> UPPER -> DIGIT
0,
(5 << 16) + 30, // MIXED -> PUNCT
},
{
(5 << 16) + 31, // PUNCT -> UPPER
(10 << 16) + (31 << 5) + 28, // PUNCT -> UPPER -> LOWER
(10 << 16) + (31 << 5) + 30, // PUNCT -> UPPER -> DIGIT
(10 << 16) + (31 << 5) + 29, // PUNCT -> UPPER -> MIXED
0,
},
};
// A reverse mapping from [mode][char] to the encoding for that character
// in that mode. An entry of 0 indicates no mapping exists.
private static final int[][] CHAR_MAP = new int[5][256];
static {
CHAR_MAP[MODE_UPPER][' '] = 1;
for (int c = 'A'; c <= 'Z'; c++) {
CHAR_MAP[MODE_UPPER][c] = c - 'A' + 2;
}
CHAR_MAP[MODE_LOWER][' '] = 1;
for (int c = 'a'; c <= 'z'; c++) {
CHAR_MAP[MODE_LOWER][c] = c - 'a' + 2;
}
CHAR_MAP[MODE_DIGIT][' '] = 1;
for (int c = '0'; c <= '9'; c++) {
CHAR_MAP[MODE_DIGIT][c] = c - '0' + 2;
}
CHAR_MAP[MODE_DIGIT][','] = 12;
CHAR_MAP[MODE_DIGIT]['.'] = 13;
int[] mixedTable = {
'\0', ' ', '\1', '\2', '\3', '\4', '\5', '\6', '\7', '\b', '\t', '\n',
'\13', '\f', '\r', '\33', '\34', '\35', '\36', '\37', '@', '\\', '^',
'_', '`', '|', '~', '\177'
};
for (int i = 0; i < mixedTable.length; i++) {
CHAR_MAP[MODE_MIXED][mixedTable[i]] = i;
}
int[] punctTable = {
'\0', '\r', '\0', '\0', '\0', '\0', '!', '\'', '#', '$', '%', '&', '\'',
'(', ')', '*', '+', ',', '-', '.', '/', ':', ';', '<', '=', '>', '?',
'[', ']', '{', '}'
};
for (int i = 0; i < punctTable.length; i++) {
if (punctTable[i] > 0) {
CHAR_MAP[MODE_PUNCT][punctTable[i]] = i;
}
}
}
// A map showing the available shift codes. (The shifts to BINARY are not
// shown
static final int[][] SHIFT_TABLE = new int[6][6]; // mode shift codes, per table
static {
for (int[] table : SHIFT_TABLE) {
Arrays.fill(table, -1);
}
SHIFT_TABLE[MODE_UPPER][MODE_PUNCT] = 0;
SHIFT_TABLE[MODE_LOWER][MODE_PUNCT] = 0;
SHIFT_TABLE[MODE_LOWER][MODE_UPPER] = 28;
SHIFT_TABLE[MODE_MIXED][MODE_PUNCT] = 0;
SHIFT_TABLE[MODE_DIGIT][MODE_PUNCT] = 0;
SHIFT_TABLE[MODE_DIGIT][MODE_UPPER] = 15;
}
private final byte[] text;
public HighLevelEncoder(byte[] text) {
this.text = text;
}
/**
* @return text represented by this encoder encoded as a {@link BitArray}
*/
public BitArray encode() {
Collection states = Collections.singletonList(State.INITIAL_STATE);
for (int index = 0; index < text.length; index++) {
int pairCode;
int nextChar = index + 1 < text.length ? text[index + 1] : 0;
switch (text[index]) {
case '\r':
pairCode = nextChar == '\n' ? 2 : 0;
break;
case '.' :
pairCode = nextChar == ' ' ? 3 : 0;
break;
case ',' :
pairCode = nextChar == ' ' ? 4 : 0;
break;
case ':' :
pairCode = nextChar == ' ' ? 5 : 0;
break;
default:
pairCode = 0;
}
if (pairCode > 0) {
// We have one of the four special PUNCT pairs. Treat them specially.
// Get a new set of states for the two new characters.
states = updateStateListForPair(states, index, pairCode);
index++;
} else {
// Get a new set of states for the new character.
states = updateStateListForChar(states, index);
}
}
// We are left with a set of states. Find the shortest one.
State minState = Collections.min(states, new Comparator() {
@Override
public int compare(State a, State b) {
return a.getBitCount() - b.getBitCount();
}
});
// Convert it to a bit array, and return.
return minState.toBitArray(text);
}
// We update a set of states for a new character by updating each state
// for the new character, merging the results, and then removing the
// non-optimal states.
private Collection updateStateListForChar(Iterable states, int index) {
Collection result = new LinkedList<>();
for (State state : states) {
updateStateForChar(state, index, result);
}
return simplifyStates(result);
}
// Return a set of states that represent the possible ways of updating this
// state for the next character. The resulting set of states are added to
// the "result" list.
private void updateStateForChar(State state, int index, Collection result) {
char ch = (char) (text[index] & 0xFF);
boolean charInCurrentTable = CHAR_MAP[state.getMode()][ch] > 0;
State stateNoBinary = null;
for (int mode = 0; mode <= MODE_PUNCT; mode++) {
int charInMode = CHAR_MAP[mode][ch];
if (charInMode > 0) {
if (stateNoBinary == null) {
// Only create stateNoBinary the first time it's required.
stateNoBinary = state.endBinaryShift(index);
}
// Try generating the character by latching to its mode
if (!charInCurrentTable || mode == state.getMode() || mode == MODE_DIGIT) {
// If the character is in the current table, we don't want to latch to
// any other mode except possibly digit (which uses only 4 bits). Any
// other latch would be equally successful *after* this character, and
// so wouldn't save any bits.
State latchState = stateNoBinary.latchAndAppend(mode, charInMode);
result.add(latchState);
}
// Try generating the character by switching to its mode.
if (!charInCurrentTable && SHIFT_TABLE[state.getMode()][mode] >= 0) {
// It never makes sense to temporarily shift to another mode if the
// character exists in the current mode. That can never save bits.
State shiftState = stateNoBinary.shiftAndAppend(mode, charInMode);
result.add(shiftState);
}
}
}
if (state.getBinaryShiftByteCount() > 0 || CHAR_MAP[state.getMode()][ch] == 0) {
// It's never worthwhile to go into binary shift mode if you're not already
// in binary shift mode, and the character exists in your current mode.
// That can never save bits over just outputting the char in the current mode.
State binaryState = state.addBinaryShiftChar(index);
result.add(binaryState);
}
}
private static Collection updateStateListForPair(Iterable states, int index, int pairCode) {
Collection result = new LinkedList<>();
for (State state : states) {
updateStateForPair(state, index, pairCode, result);
}
return simplifyStates(result);
}
private static void updateStateForPair(State state, int index, int pairCode, Collection result) {
State stateNoBinary = state.endBinaryShift(index);
// Possibility 1. Latch to MODE_PUNCT, and then append this code
result.add(stateNoBinary.latchAndAppend(MODE_PUNCT, pairCode));
if (state.getMode() != MODE_PUNCT) {
// Possibility 2. Shift to MODE_PUNCT, and then append this code.
// Every state except MODE_PUNCT (handled above) can shift
result.add(stateNoBinary.shiftAndAppend(MODE_PUNCT, pairCode));
}
if (pairCode == 3 || pairCode == 4) {
// both characters are in DIGITS. Sometimes better to just add two digits
State digitState = stateNoBinary
.latchAndAppend(MODE_DIGIT, 16 - pairCode) // period or comma in DIGIT
.latchAndAppend(MODE_DIGIT, 1); // space in DIGIT
result.add(digitState);
}
if (state.getBinaryShiftByteCount() > 0) {
// It only makes sense to do the characters as binary if we're already
// in binary mode.
State binaryState = state.addBinaryShiftChar(index).addBinaryShiftChar(index + 1);
result.add(binaryState);
}
}
private static Collection simplifyStates(Iterable states) {
List result = new LinkedList<>();
for (State newState : states) {
boolean add = true;
for (Iterator iterator = result.iterator(); iterator.hasNext();) {
State oldState = iterator.next();
if (oldState.isBetterThanOrEqualTo(newState)) {
add = false;
break;
}
if (newState.isBetterThanOrEqualTo(oldState)) {
iterator.remove();
}
}
if (add) {
result.add(newState);
}
}
return result;
}
}