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Merge pull request #1226 from notmasteryet/tree-80

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Rewrite predictor code to avoid writing into subarrays.
This commit is contained in:
Artur Adib 2012-02-17 07:56:02 -08:00
commit dd53edffad
1 changed files with 26 additions and 21 deletions
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src/stream.js
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@ -623,7 +623,6 @@ var PredictorStream = (function PredictorStreamClosure() {
var bufferLength = this.bufferLength;
var buffer = this.ensureBuffer(bufferLength + rowBytes);
var currentRow = buffer.subarray(bufferLength, bufferLength + rowBytes);
var bits = this.bits;
var colors = this.colors;
@ -632,6 +631,7 @@ var PredictorStream = (function PredictorStreamClosure() {
var inbuf = 0, outbuf = 0;
var inbits = 0, outbits = 0;
var pos = bufferLength;
if (bits === 1) {
for (var i = 0; i < rowBytes; ++i) {
@ -639,19 +639,21 @@ var PredictorStream = (function PredictorStreamClosure() {
inbuf = (inbuf << 8) | c;
// bitwise addition is exclusive or
// first shift inbuf and then add
currentRow[i] = (c ^ (inbuf >> colors)) & 0xFF;
buffer[pos++] = (c ^ (inbuf >> colors)) & 0xFF;
// truncate inbuf (assumes colors < 16)
inbuf &= 0xFFFF;
}
} else if (bits === 8) {
for (var i = 0; i < colors; ++i)
currentRow[i] = rawBytes[i];
for (; i < rowBytes; ++i)
currentRow[i] = currentRow[i - colors] + rawBytes[i];
buffer[pos++] = rawBytes[i];
for (; i < rowBytes; ++i) {
buffer[pos] = buffer[pos - colors] + rawBytes[i];
pos++;
}
} else {
var compArray = new Uint8Array(colors + 1);
var bitMask = (1 << bits) - 1;
var j = 0, k = 0;
var j = 0, k = bufferLength;
var columns = this.columns;
for (var i = 0; i < columns; ++i) {
for (var kk = 0; kk < colors; ++kk) {
@ -665,13 +667,13 @@ var PredictorStream = (function PredictorStreamClosure() {
outbuf = (outbuf << bits) | compArray[kk];
outbits += bits;
if (outbits >= 8) {
currentRow[k++] = (outbuf >> (outbits - 8)) & 0xFF;
buffer[k++] = (outbuf >> (outbits - 8)) & 0xFF;
outbits -= 8;
}
}
}
if (outbits > 0) {
currentRow[k++] = (outbuf << (8 - outbits)) +
buffer[k++] = (outbuf << (8 - outbits)) +
(inbuf & ((1 << (8 - outbits)) - 1));
}
}
@ -690,32 +692,35 @@ var PredictorStream = (function PredictorStreamClosure() {
var bufferLength = this.bufferLength;
var buffer = this.ensureBuffer(bufferLength + rowBytes);
var currentRow = buffer.subarray(bufferLength, bufferLength + rowBytes);
var prevRow = buffer.subarray(bufferLength - rowBytes, bufferLength);
if (prevRow.length == 0)
prevRow = new Uint8Array(rowBytes);
var j = bufferLength;
switch (predictor) {
case 0:
for (var i = 0; i < rowBytes; ++i)
currentRow[i] = rawBytes[i];
buffer[j++] = rawBytes[i];
break;
case 1:
for (var i = 0; i < pixBytes; ++i)
currentRow[i] = rawBytes[i];
for (; i < rowBytes; ++i)
currentRow[i] = (currentRow[i - pixBytes] + rawBytes[i]) & 0xFF;
buffer[j++] = rawBytes[i];
for (; i < rowBytes; ++i) {
buffer[j] = (buffer[j - pixBytes] + rawBytes[i]) & 0xFF;
j++;
}
break;
case 2:
for (var i = 0; i < rowBytes; ++i)
currentRow[i] = (prevRow[i] + rawBytes[i]) & 0xFF;
buffer[j++] = (prevRow[i] + rawBytes[i]) & 0xFF;
break;
case 3:
for (var i = 0; i < pixBytes; ++i)
currentRow[i] = (prevRow[i] >> 1) + rawBytes[i];
buffer[j++] = (prevRow[i] >> 1) + rawBytes[i];
for (; i < rowBytes; ++i) {
currentRow[i] = (((prevRow[i] + currentRow[i - pixBytes]) >> 1) +
buffer[j] = (((prevRow[i] + buffer[j - pixBytes]) >> 1) +
rawBytes[i]) & 0xFF;
j++;
}
break;
case 4:
@ -724,12 +729,12 @@ var PredictorStream = (function PredictorStreamClosure() {
for (var i = 0; i < pixBytes; ++i) {
var up = prevRow[i];
var c = rawBytes[i];
currentRow[i] = up + c;
buffer[j++] = up + c;
}
for (; i < rowBytes; ++i) {
var up = prevRow[i];
var upLeft = prevRow[i - pixBytes];
var left = currentRow[i - pixBytes];
var left = buffer[j - pixBytes];
var p = left + up - upLeft;
var pa = p - left;
@ -744,11 +749,11 @@ var PredictorStream = (function PredictorStreamClosure() {
var c = rawBytes[i];
if (pa <= pb && pa <= pc)
currentRow[i] = left + c;
buffer[j++] = left + c;
else if (pb <= pc)
currentRow[i] = up + c;
buffer[j++] = up + c;
else
currentRow[i] = upLeft + c;
buffer[j++] = upLeft + c;
}
break;
default: