JPEGView/Source/C/CopyReallyFastScaledFrom32.c

/*********************************************************/
/* This source code copyright (c) 1991-2001, Aaron Giles */
/* See the Read Me file for licensing information.       */
/* Contact email: mac@aarongiles.com                     */
/*********************************************************/

// void CopyScaledFrom32(CopyDataPtr theData);
#define One (1L << 16)
	DitherErrorsPtr eBuffer,			// pointers to whichever dithering
					oBuffer;			// 		buffers we decide to use
	ulong *scaled,				 		// pointer to the start of the scaling buffer
		  *srcScaled, 					// temp. source pointer used during scaling
		  *dstScaled;					// destination pointer used during scaling
	Ptr src = theData->srcBase, 		// source pointer into original image data
		dst = theData->dstBase;			// dest. pointer into real destination
	ulong srcPixelContributionY, 		// contribution in Y made by each source pixel
		  srcPixelContributionX, 		// contribution in X made by each source pixel
		  srcRemainingY = theData->yRemainder,// remaining Y contribution for source
		  srcRemainingX;				// remaining X contribution for current src
	ulong dstNeededY, 					// amount needed for complete dest. Y pixel
		  dstNeededX;					// amount needed for complete dest. X pixel
	short *rgnPtr; 						// pointer to the region data
	long row = theData->height, 		// row counter
		  col;							// column counter
	Handle dynamicBuffer;				// handle to any allocation we make
	RgnBuffer rgnData;					// buffer for the region data
	DitherErrors evenDithering[kStackRowWidth + 2], 	// stack-based buffers for dithering; if these
				 oddDithering[kStackRowWidth + 2];	// 		aren't enough, we allocate bigger ones
	ulong scaledRow[kStackRowWidth + 2];				// stack-based buffer for scaling

	// Allocate space for our buffers, if not enough room on stack
	// NOTE: This only works if the machine is in 32-bit addressing mode!!!
	if (theData->width > kStackRowWidth) {
		dynamicBuffer = AnyNewHandle((theData->width + 2) * (2 * sizeof(DitherErrors) + sizeof(ulong)));
		if (!dynamicBuffer) return;
		HLock(dynamicBuffer);
		eBuffer = (DitherErrorsPtr)*dynamicBuffer + 1;
		oBuffer = eBuffer + theData->width + 2;
		scaled = (ulong *)(oBuffer + theData->width + 1) + 1;
	} else {
		eBuffer = &evenDithering[1];
		oBuffer = &oddDithering[1];
	}
	scaled = &scaledRow[1];
	
	// Clear out the dithering and scaling buffers
	if (theData->evodd & 1) 
		ClearMem((Ptr)&eBuffer[-1], (theData->width + 2) * sizeof(DitherErrors));
	else ClearMem((Ptr)&oBuffer[-1], (theData->width + 2) * sizeof(DitherErrors));
	
	// Initialize the region data
	rgnData.zero = 0;
	rgnPtr = InitRegion(*theData->theRgn, &rgnData, &theData->boxRect);
	
	// Set up the source/destination quantities
	srcPixelContributionY = (theData->dstHeight << 16) / theData->srcHeight + 1;
	srcPixelContributionX = (theData->dstWidth << 16) / theData->srcWidth + 1;

	// The outermost (row) loop begins here; set up our pointers into the data
	while (row--) {
		srcScaled = (ulong *)src;
		dstScaled = (ulong *)scaled;
	
		// reset the columns counter and reset the source X remainder
		col = theData->width;
		srcRemainingX = theData->xRemainder;

		// The inner (column) loops begin here; set up our counters in the dest system
		if (One >= srcRemainingY) {
			if ((One - srcRemainingY) < srcPixelContributionY)
				srcScaled += ((One - srcRemainingY) < srcRemainingY) ?
							0 : (theData->srcRow >> 2);
			else srcScaled += (theData->srcRow >> 2);
		}

		while (col--) {
			dstNeededX = One;
			if (dstNeededX < srcRemainingX)
				*dstScaled++ = *srcScaled;
			else if ((dstNeededX -= srcRemainingX) < srcPixelContributionX) {
				if (dstNeededX < srcRemainingX) *dstScaled++ = *srcScaled++;
				else *dstScaled++ = *++srcScaled;
				srcRemainingX = srcPixelContributionX;
			} else {
				*dstScaled++ = *++srcScaled;
				srcScaled++;
			ScaleLoop1:
				if ((dstNeededX -= srcPixelContributionX) >= srcPixelContributionX) {
					srcScaled++;
					goto ScaleLoop1;
				}
				srcRemainingX = srcPixelContributionX;
			}
			// apply the final adjustment to the X counters
			srcRemainingX -= dstNeededX;
		}
		
		// We now have a row; set up to do a dithered copy from it
		if ((++theData->evodd) & 1)
			theData->odd(scaled, dst, theData->itAddr, theData->ctAddr, eBuffer, oBuffer,
						 rgnData.buffer, theData->errTable, theData->width);
		else theData->even(scaled, dst, theData->itAddr, theData->ctAddr, eBuffer, oBuffer,
						 rgnData.buffer, theData->errTable, theData->width);

		if (!row) break;
		if (!--rgnData.yCount) rgnPtr = UpdateRegion(rgnPtr, &rgnData, &theData->boxRect);

		// apply final adjustments to the Y counters
		dstNeededY = 1L << 16;
		while (dstNeededY >= srcRemainingY) {
			src += theData->srcRow;
			dstNeededY -= srcRemainingY;
			srcRemainingY = srcPixelContributionY;
		}
		srcRemainingY -= dstNeededY;
		dst += theData->dstRow;
	}
	
	// Return space allocated for buffers
	if (theData->width > kStackRowWidth) DisposeHandle(dynamicBuffer);