Revamped Java QrSegmentAdvanced code to implement optimization of kanji text, and simplify existing algorithms.
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Project Nayuki
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@ -25,6 +25,7 @@ package io.nayuki.qrcodegen;
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import static io.nayuki.qrcodegen.QrSegment.Mode.ALPHANUMERIC;
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import static io.nayuki.qrcodegen.QrSegment.Mode.BYTE;
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import static io.nayuki.qrcodegen.QrSegment.Mode.KANJI;
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import static io.nayuki.qrcodegen.QrSegment.Mode.NUMERIC;
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import java.nio.charset.StandardCharsets;
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import java.util.ArrayList;
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@ -42,10 +43,10 @@ public final class QrSegmentAdvanced {
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/**
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* Returns a new mutable list of zero or more segments to represent the specified Unicode text string.
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* The resulting list optimally minimizes the total encoded bit length, subjected to the constraints given
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* by the specified {error correction level, minimum version number, maximum version number}, plus the additional
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* constraint that the segment modes {NUMERIC, ALPHANUMERIC, BYTE} can be used but KANJI cannot be used.
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* <p>This function can be viewed as a significantly more sophisticated and slower replacement
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* for {@link QrSegment#makeSegments(String)}, but requiring more input parameters in a way
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* by the specified {error correction level, minimum version number, maximum version number}.
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* <p>This function can utilize all four text encoding modes: numeric, alphanumeric, byte, and kanji.
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* This can be viewed as a significantly more sophisticated and slower replacement for
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* {@link QrSegment#makeSegments(String)}, but requiring more input parameters in a way
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* that overlaps with {@link QrCode#encodeSegments(List,QrCode.Ecc,int,int,int,boolean)}.</p>
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* @param text the text to be encoded, which can be any Unicode string
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* @param ecl the error correction level to use
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@ -83,102 +84,104 @@ public final class QrSegmentAdvanced {
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private static List<QrSegment> makeSegmentsOptimally(String text, int version) {
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if (text.length() == 0)
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return new ArrayList<>();
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byte[] data = text.getBytes(StandardCharsets.UTF_8);
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int[][] bitCosts = computeBitCosts(data, version);
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Mode[] charModes = computeCharacterModes(data, version, bitCosts);
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return splitIntoSegments(data, charModes);
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int[] codePoints = toCodePoints(text);
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Mode[] charModes = computeCharacterModes(codePoints, version);
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return splitIntoSegments(codePoints, charModes);
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}
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private static int[][] computeBitCosts(byte[] data, int version) {
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// Segment header sizes, measured in 1/6 bits
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int bytesCost = (4 + BYTE .numCharCountBits(version)) * 6;
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int alphnumCost = (4 + ALPHANUMERIC.numCharCountBits(version)) * 6;
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int numberCost = (4 + NUMERIC .numCharCountBits(version)) * 6;
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// result[mode][len] is the number of 1/6 bits to encode the first len characters of the text, ending in the mode
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int[][] result = new int[3][data.length + 1];
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Arrays.fill(result[1], Integer.MAX_VALUE / 2);
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Arrays.fill(result[2], Integer.MAX_VALUE / 2);
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result[0][0] = bytesCost;
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result[1][0] = alphnumCost;
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result[2][0] = numberCost;
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// Calculate the cost table using dynamic programming
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for (int i = 0; i < data.length; i++) {
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// Encode a character
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int j = i + 1;
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char c = (char)data[i];
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result[0][j] = result[0][i] + 48; // 8 bits per byte
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if (isAlphanumeric(c))
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result[1][j] = result[1][i] + 33; // 5.5 bits per alphanumeric char
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if (isNumeric(c))
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result[2][j] = result[2][i] + 20; // 3.33 bits per digit
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// Switch modes, rounding up fractional bits
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result[0][j] = Math.min(roundUp6(Math.min(result[1][j], result[2][j])) + bytesCost , result[0][j]);
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result[1][j] = Math.min(roundUp6(Math.min(result[2][j], result[0][j])) + alphnumCost, result[1][j]);
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result[2][j] = Math.min(roundUp6(Math.min(result[0][j], result[1][j])) + numberCost , result[2][j]);
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}
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return result;
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}
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private static Mode[] computeCharacterModes(byte[] data, int version, int[][] bitCosts) {
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if (data.length == 0)
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private static Mode[] computeCharacterModes(int[] codePoints, int version) {
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if (codePoints.length == 0)
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throw new IllegalArgumentException();
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final Mode[] modeTypes = {BYTE, ALPHANUMERIC, NUMERIC, KANJI}; // Do not modify
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final int numModes = modeTypes.length;
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// Segment header sizes, measured in 1/6 bits
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int bytesCost = (4 + BYTE .numCharCountBits(version)) * 6;
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int alphnumCost = (4 + ALPHANUMERIC.numCharCountBits(version)) * 6;
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int numberCost = (4 + NUMERIC .numCharCountBits(version)) * 6;
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final int[] headCosts = new int[numModes];
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for (int i = 0; i < numModes; i++)
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headCosts[i] = (4 + modeTypes[i].numCharCountBits(version)) * 6;
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// Infer the mode used for last character by taking the minimum
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Mode curMode;
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int end = bitCosts[0].length - 1;
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if (bitCosts[0][end] <= Math.min(bitCosts[1][end], bitCosts[2][end]))
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curMode = BYTE;
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else if (bitCosts[1][end] <= bitCosts[2][end])
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curMode = ALPHANUMERIC;
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else
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curMode = NUMERIC;
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// charModes[i][j] represents the mode to encode the code point at
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// index i such that the final segment ends in modeTypes[j] and the
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// total number of bits is minimized over all possible choices
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Mode[][] charModes = new Mode[codePoints.length][numModes];
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// Work backwards to calculate optimal encoding mode for each character
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Mode[] result = new Mode[data.length];
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result[data.length - 1] = curMode;
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for (int i = data.length - 2; i >= 0; i--) {
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char c = (char)data[i];
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if (curMode == NUMERIC) {
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if (isNumeric(c))
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curMode = NUMERIC;
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else if (isAlphanumeric(c) && roundUp6(bitCosts[1][i] + 33) + numberCost == bitCosts[2][i + 1])
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curMode = ALPHANUMERIC;
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// At the beginning of each iteration of the loop below,
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// prevCosts[j] is the exact minimum number of 1/6 bits needed to
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// encode the entire string prefix of length i, and end in modeTypes[j]
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int[] prevCosts = headCosts.clone();
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// Calculate costs using dynamic programming
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for (int i = 0; i < codePoints.length; i++) {
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int c = codePoints[i];
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int[] curCosts = new int[numModes];
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{ // Always extend a bytes segment
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int b;
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if (c < 0x80)
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b = 1;
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else if (c < 0x800)
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b = 2;
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else if (c < 0x10000)
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b = 3;
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else
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curMode = BYTE;
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} else if (curMode == ALPHANUMERIC) {
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if (isNumeric(c) && roundUp6(bitCosts[2][i] + 20) + alphnumCost == bitCosts[1][i + 1])
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curMode = NUMERIC;
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else if (isAlphanumeric(c))
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curMode = ALPHANUMERIC;
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else
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curMode = BYTE;
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} else if (curMode == BYTE) {
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if (isNumeric(c) && roundUp6(bitCosts[2][i] + 20) + bytesCost == bitCosts[0][i + 1])
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curMode = NUMERIC;
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else if (isAlphanumeric(c) && roundUp6(bitCosts[1][i] + 33) + bytesCost == bitCosts[0][i + 1])
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curMode = ALPHANUMERIC;
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else
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curMode = BYTE;
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} else
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throw new AssertionError();
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result[i] = curMode;
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b = 4;
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curCosts[0] = prevCosts[0] + b * 8 * 6;
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charModes[i][0] = modeTypes[0];
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}
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// Extend a segment if possible
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if (isAlphanumeric(c)) {
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curCosts[1] = prevCosts[1] + 33; // 5.5 bits per alphanumeric char
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charModes[i][1] = modeTypes[1];
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}
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if (isNumeric(c)) {
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curCosts[2] = prevCosts[2] + 20; // 3.33 bits per digit
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charModes[i][2] = modeTypes[2];
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}
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if (isKanji(c)) {
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curCosts[3] = prevCosts[3] + 104; // 13 bits per Shift JIS char
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charModes[i][3] = modeTypes[3];
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}
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// Start new segment at the end to switch modes
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for (int j = 0; j < numModes; j++) { // To mode
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for (int k = 0; k < numModes; k++) { // From mode
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int newCost = roundUp6(curCosts[k]) + headCosts[j];
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if (charModes[i][k] != null && (charModes[i][j] == null || newCost < curCosts[j])) {
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curCosts[j] = newCost;
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charModes[i][j] = modeTypes[k];
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}
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}
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}
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prevCosts = curCosts;
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}
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// Find optimal ending mode
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Mode curMode = null;
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for (int i = 0, minCost = 0; i < numModes; i++) {
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if (curMode == null || prevCosts[i] < minCost) {
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minCost = prevCosts[i];
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curMode = modeTypes[i];
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}
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}
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// Get optimal mode for each code point by tracing backwards
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Mode[] result = new Mode[charModes.length];
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for (int i = result.length - 1; i >= 0; i--) {
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for (int j = 0; j < numModes; j++) {
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if (modeTypes[j] == curMode) {
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curMode = charModes[i][j];
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result[i] = curMode;
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break;
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}
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}
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}
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return result;
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}
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private static List<QrSegment> splitIntoSegments(byte[] data, Mode[] charModes) {
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if (data.length == 0)
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private static List<QrSegment> splitIntoSegments(int[] codePoints, Mode[] charModes) {
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if (codePoints.length == 0)
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throw new IllegalArgumentException();
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List<QrSegment> result = new ArrayList<>();
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@ -186,20 +189,20 @@ public final class QrSegmentAdvanced {
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Mode curMode = charModes[0];
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int start = 0;
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for (int i = 1; ; i++) {
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if (i < data.length && charModes[i] == curMode)
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if (i < codePoints.length && charModes[i] == curMode)
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continue;
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String s = new String(codePoints, start, i - start);
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if (curMode == BYTE)
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result.add(QrSegment.makeBytes(Arrays.copyOfRange(data, start, i)));
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else {
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String temp = new String(data, start, i - start, StandardCharsets.US_ASCII);
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if (curMode == NUMERIC)
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result.add(QrSegment.makeNumeric(temp));
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else if (curMode == ALPHANUMERIC)
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result.add(QrSegment.makeAlphanumeric(temp));
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else
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throw new AssertionError();
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}
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if (i >= data.length)
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result.add(QrSegment.makeBytes(s.getBytes(StandardCharsets.UTF_8)));
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else if (curMode == NUMERIC)
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result.add(QrSegment.makeNumeric(s));
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else if (curMode == ALPHANUMERIC)
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result.add(QrSegment.makeAlphanumeric(s));
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else if (curMode == KANJI)
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result.add(makeKanji(s));
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else
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throw new AssertionError();
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if (i >= codePoints.length)
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return result;
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curMode = charModes[i];
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start = i;
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@ -207,6 +210,16 @@ public final class QrSegmentAdvanced {
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}
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private static int[] toCodePoints(String s) {
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int[] result = s.codePoints().toArray();
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for (int c : result) {
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if (Character.isSurrogate((char)c))
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throw new IllegalArgumentException("Invalid UTF-16 string");
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}
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return result;
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}
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private static boolean isAlphanumeric(int c) {
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return isNumeric(c) || 'A' <= c && c <= 'Z' || " $%*+./:-".indexOf(c) != -1;
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}
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