:TITLE[JasmineHalftone];

%Edit by Fiala 16 July 1981: Harmonize with Pilot; change register assignments
to use more of available Stack registers; eliminate returnLoc register; add
prefix jh to register names.
Edit by Fiala 7 January 1981: Harmonize with Alto system; bum many mi.
Created by Maleson 3 April 1980.

Floyd-Steinberg error distribution halftoning,
	"REPLACE" mode doesn't work for all modes (save space)
%
SetTask[0];

*jhTemp1 (RM 5) and jhTemp2 (RM 7) are also used.
:IF[AltoMode]; **********************************
RV4[jhErrorVec,jhErrorVecHi,jhScreenWord,jhScreenWordHi,44];
RV4[jhBitCount,jhBitmapWidth,jhPixelArray,jhPixelArrayHi,50];
RV4[jhNInputPixels,jhBlackVal,jhRange,jhNOutputDots,10];

RV2[jhAddrTemp,jhAddrTempHi,14];

RV[jhCascadeRight,56];
RV[jhCascadeDiag,57];
RV[jhBitVal,66];
RV[jhJCtr,67];
RV[jhX,2];
RV[jhVal,3];
RV[jhErrorTemp,4];
RV[jhTemp1,5];
RV[jhTemp2,7];
:ELSE; ******************************************
*It seems that RM 6, 16-17 and 70-73 are available temporaries.
RV4[jhErrorVec,jhErrorVecHi,jhScreenWord,jhScreenWordHi,44];
RV4[jhBitCount,jhBitmapWidth,jhPixelArray,jhPixelArrayHi,50];
RV4[jhNInputPixels,jhBlackVal,jhRange,jhNOutputDots,10];

RV2[jhAddrTemp,jhAddrTempHi,14];

RV[jhCascadeRight,56];
RV[jhCascadeDiag,57];
RV[jhBitVal,66];
RV[jhJCtr,67];
RV[jhX,2];
RV[jhVal,3];
RV[jhErrorTemp,4];
RV[jhTemp1,5];
RV[jhTemp2,7];
:ENDIF; *****************************************

OnPage[HalftonePage];

***Find out whether MDShi should be used here and/or in Jasmine.Mc instead of
***0C for the high base register value.
@JHalfTone:
	jhAddrTempHi _ 0C, At[PrintLine];
	T _ Stack;
	jhAddrTemp _ T;
	PFetch4[jhAddrTemp,jhErrorVec,4];
	PFetch4[jhAddrTemp,jhBitCount,10];
	T _ LSh[jhErrorVecHi,10], Task;
	jhErrorVecHi _ (jhErrorVecHi) + T + 1;
	T _ LSh[jhScreenWordHi,10];
	jhScreenWordHi _ (jhScreenWordHi) + T;	*no +1, for negative adds;
	PFetch4[jhAddrTemp,jhNInputPixels,0], Task;
	T _ LSh[jhPixelArrayHi,10];
	jhPixelArrayHi _ (jhPixelArrayHi) + T + 1;
	T _ LdF[jhBitCount,14,4];
	jhBitVal _ 17C;
	jhBitVal _ (jhBitVal) - T;
	CycleControl _ jhBitVal;
	jhBitVal _ 100000C;
*jhBitVal _ 100000b rsh (jhBitCount[12d:15d])
	jhBitVal _ WFA[jhBitVal];
	T _ jhBitCount;
	PFetch1[jhErrorVec,jhCascadeRight];
	T _ jhNOutputDots;
	jhJCtr _ (Zero) - T;
	jhCascadeDiag _ Zero;
	jhCascadeRight _ (LSh[jhCascadeRight,2]) - 1;
	T _ jhNInputPixels;
	jhTemp1 _ T;
	T _ LdF[jhBitmapWidth,4,1];
	jhNInputPixels _ (jhNInputPixels) + T; 
	jhX _ T, GoTo[forX0];

*subroutines: pieces used by all four modes
GetPixel:
	T _ RSh[jhX,1], GoTo[xDone,ALU<0];
	PFetch1[jhPixelArray,jhVal];
	T _ jhBlackVal;
	LU _ jhX, GoTo[xOdd,R Odd];
xEven:	jhVal _ T _ (RSh[jhVal,10]) - T, GoTo[blackCheck];
xOdd:	jhVal _ T _ (RHMask[jhVal]) - T, GoTo[blackCheck];
blackCheck:
	LU _ (jhRange) - T, GoTo[blackOK,ALU>=0];
	jhVal _ Zero, Return;
blackOK:
	T _ jhRange, GoTo[whiteOK,ALU>=0];
	jhVal _ T, Return;
whiteOK:	Return;

OrBlack:
	PFetch1[jhScreenWord,jhTemp2];
	T _ jhBitVal;
	jhTemp2 _ (jhTemp2) or T, Return;

NotWhite:
	PFetch1[jhScreenWord,jhTemp2];
	T _ jhBitVal;
	jhTemp2 _ (jhTemp2) and not T, Return;

StoreVal:
	PStore1[jhScreenWord,jhTemp2], Return;

GetError: 
	jhCascadeRight _ (RSh[jhCascadeRight,1]) or T, GoTo[a1,R Odd];
a0:	T _ (RSh[jhCascadeRight,1]) or T, GoTo[a00,R Even];
a01:	jhCascadeRight _ (jhCascadeRight) + 1;
a00:	jhErrorTemp _ T, GoTo[haveError];

a1:	T _ (RSh[jhCascadeRight,1]) or T, GoTo[a10,R Even];
a11:	jhErrorTemp _ T _ (Zero) + T + 1, GoTo[haveError];
a10:	jhCascadeRight _ (jhCascadeRight) + 1, GoTo[a00];
haveError:
	jhCascadeDiag _ (jhCascadeDiag) + T;	
	T _ jhBitCount;
	PStore1[jhErrorVec,jhCascadeDiag], Return;
GetNext:
	PFetch1[jhErrorVec,jhTemp2];
	T _ jhErrorTemp;
	jhCascadeDiag _ T;
	T _ jhTemp2;
	jhCascadeRight _ (jhCascadeRight) + T;
	T _ jhTemp1, Return;

xDone:	LoadPageExternal[opPage3];
	GoToExternal[P7TailLoc];

forX0:	LU _ (jhNInputPixels) - T - 1, Call[GetPixel];
	T _ jhJCtr, GoTo[jDone0,R>=0];
whileJ0: 
	T _ jhVal;
	jhCascadeRight _ (jhCascadeRight) + T;
	T _ jhRange, GoTo[White0,ALU>=0];
Black0: T _ LdF[jhBitCount,0,14], Call[OrBlack];
	T _ LdF[jhBitCount,0,14], Call[StoreVal];
EndDot0:
	T _ (jhCascadeRight) and (100000C), Call[GetError];
	jhBitCount _ T _ (jhBitCount) + 1, Call[GetNext];
	jhJCtr _ (jhJCtr) + T;
	jhBitVal _ RCy[jhBitVal,1], GoTo[whileJ0,ALU<0];
jDone0:	T _ jhNOutputDots;
	jhJCtr _ (jhJCtr) - T;
	jhX _ T _ (jhX) + 1, GoTo[forX0]; *could save 7 mi if jhJCtr still negative

White0: jhCascadeRight _ (jhCascadeRight) - T;
	T _ LdF[jhBitCount,0,14], Call[NotWhite];
	T _ LdF[jhBitCount,0,14];
	PStore1[jhScreenWord,jhTemp2], GoTo[EndDot0];

:END[JasmineHalftone];
(2048)\f5