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Move invariant bits out of updateScreen's inner loop

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This commit is contained in:
Jeff Parsons 2016-05-02 16:32:12 -07:00
commit 7bc35ad9af
1 changed files with 10 additions and 8 deletions
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18
modules/pc8080/lib/video.js
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@ -274,6 +274,14 @@ Video.prototype.updateScreen = function(n)
var xBuffer = 0, yBuffer = 0;
var xDirty = this.cxBuffer, xMaxDirty = 0, yDirty = this.cyBuffer, yMaxDirty = 0;
var nShiftInit = 0;
var nShiftPixel = this.nBitsPerPixel;
var nMask = (1 << nShiftPixel) - 1;
if (this.iBitFirstPixel) {
nShiftPixel = -nShiftPixel;
nShiftInit = 16 + nShiftPixel;
}
while (addr < addrLimit) {
var data = this.bus.getShortDirect(addr);
this.assert(iCell < this.aCellCache.length);
@ -281,14 +289,8 @@ Video.prototype.updateScreen = function(n)
xBuffer += this.nPixelsPerCell;
} else {
this.aCellCache[iCell] = data;
var nShift = 0;
var nShiftPixel = this.nBitsPerPixel;
var nMask = (1 << nShiftPixel) - 1;
if (this.iBitFirstPixel) {
nShift = 16 - nShiftPixel;
nShiftPixel = -nShiftPixel;
data = ((data >> 8) | ((data & 0xff) << 8));
}
var nShift = nShiftInit;
if (nShiftInit) data = ((data >> 8) | ((data & 0xff) << 8));
if (xBuffer < xDirty) xDirty = xBuffer;
for (var iPixel = 0; iPixel < this.nPixelsPerCell; iPixel++) {
var bPixel = (data >> nShift) & nMask;