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Optimized bounding box tests in JBIG2's decodeBitmap

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p01 2014-03-07 12:12:45 +01:00
parent 2a9fe573c0
commit e2a4328ff2
1 changed files with 18 additions and 6 deletions
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24
src/core/jbig2.js
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@ -258,13 +258,19 @@ var Jbig2Image = (function Jbig2ImageClosure() {
changingTemplateEntries = new Uint8Array(changingTemplateEntries);
var changingEntriesLength = changingTemplateEntries.length;
// Get the safe bounding box edges from the width, height, minX, maxX, minY
var sbb_left = -minX;
var sbb_top = -minY;
var sbb_right = width - maxX;
var pseudoPixelContext = ReusedContexts[templateIndex];
var bitmap = [];
var decoder = decodingContext.decoder;
var contexts = decodingContext.contextCache.getContexts('GB');
var ltp = 0, c, j, i0, j0, k, contextLabel = 0;
var ltp = 0, c, j, i0, j0, k, contextLabel = 0, bit, shift;
for (var i = 0; i < height; i++) {
if (prediction) {
var sltp = decoder.readBit(contexts, pseudoPixelContext);
@ -283,7 +289,7 @@ var Jbig2Image = (function Jbig2ImageClosure() {
}
// Are we in the middle of a scanline, so we can reuse contextLabel
// bits?
if (i + minY > 0 && j + minX >= 0 && j + maxX < width) {
if (j >= sbb_left && j < sbb_right && i >= sbb_top) {
// If yes, we can just shift the bits that are reusable and only
// fetch the remaining ones.
contextLabel = (contextLabel << 1) & reuseMask;
@ -296,11 +302,17 @@ var Jbig2Image = (function Jbig2ImageClosure() {
} else {
// compute the contextLabel from scratch
contextLabel = 0;
for (k = 0; k < templateLength; k++) {
i0 = i + templateY[k];
var shift = templateLength - 1;
for (k = 0; k < templateLength; k++, shift--) {
j0 = j + templateX[k];
if (i0 >= 0 && j0 >= 0 && j0 < width) {
contextLabel |= bitmap[i0][j0] << (templateLength - 1 - k);
if (j0 >= 0 && j0 < width) {
i0 = i + templateY[k];
if (i0 >= 0) {
bit = bitmap[i0][j0];
if (bit) {
contextLabel |= bit << shift;
}
}
}
}
}