DIRECTORY
Basics,
BitBltOps,
PrincOps;

BitBltOpsImpl: PROGRAM
IMPORTS
Basics
EXPORTS
BitBltOps

= BEGIN OPEN Basics;

BitAddress: TYPE = PrincOps.BitAddress;
BitBltInc: TYPE = RECORD[wVal, bitVal: INT, easy: BOOL]; -- easy if value MOD bitsPerWord = 0

nulBitAddress: BitAddress = [NIL, 0, 0];
srcAddr: BitAddress;		-- address of source word at beginning of line
dstAddr: BitAddress;		-- address of destination word at beginning of line
goodDstAddr: BitAddress;	-- address of good destination word at beginning of line
srcFunc: PrincOps.SrcFunc _ null;
dstFunc: PrincOps.DstFunc _ null;
srcInc, dstInc: BitBltInc;
goingForward: BOOL _ TRUE;

isThin: BOOL _ FALSE;			-- true if dest is all within one word
lMask: WORD;
rMask: WORD;
skew: NAT;
dWidth, sWidth: INTEGER;		-- width in words, including left & right partial words
extraWordAtLeft, extraWordAtRight: BOOL;

isGray: BOOL _ FALSE;
grayParam: PrincOps.GrayParm;
grayWidth: BitBltInc;
grayBump: BitBltInc;
lastGray: [0..15);
lastBBT: PrincOps.BitBltTable;

InvalidBitBltCall: ERROR = CODE; 
HardCase: SIGNAL = CODE;
BadValueForward: SIGNAL[ATOM] = CODE;
BadValueBackward: SIGNAL[ATOM] = CODE;
BadValueThin: SIGNAL = CODE;

debugging: BOOL _ FALSE;

BitBltOpCheck: PUBLIC PROC[bbt: PrincOps.BitBltTablePtr, goodDest: BitAddress] = {
grayHeightMod: CARDINAL;
lineNum: CARDINAL _ DoSetup[bbt, goodDest];			-- which line do we start with
IF isGray THEN grayHeightMod _ grayParam.heightMinusOne+1;

WHILE lineNum IN [0..bbt.height) DO
sInc: BitBltInc;
IF goingForward THEN {
IF isGray THEN BltOneLineForwardGrayCheck[] ELSE BltOneLineForwardCheck[]
} ELSE BltOneLineBackward[];

lineNum _ lineNum + (IF goingForward THEN 1 ELSE -1);
sInc _ IF bbt.flags.gray THEN
IF (lineNum MOD grayHeightMod) = lastGray THEN grayBump ELSE grayWidth
ELSE srcInc;
IF sInc.easy AND dstInc.easy THEN {
srcAddr _ BitBltAddrInc[srcAddr, sInc];
dstAddr _ BitBltAddrInc[dstAddr, dstInc];
goodDstAddr _ BitBltAddrInc[goodDstAddr, dstInc];
}
ELSE RecomputeCheck[bbt, goodDest, sInc];
ENDLOOP;
};

BitBltOp: PUBLIC PROC[bbt: PrincOps.BitBltTablePtr] = {
grayHeightMod: CARDINAL;
lineNum: CARDINAL _ DoSetup[bbt, nulBitAddress];		-- which line do we start with
IF isGray THEN grayHeightMod _ grayParam.heightMinusOne+1;

WHILE lineNum IN [0..bbt.height) DO
sInc: BitBltInc;
IF goingForward THEN {
IF isGray THEN BltOneLineForwardGray[] ELSE BltOneLineForward[]
} ELSE BltOneLineBackwardCheck[];
lineNum _ lineNum + (IF goingForward THEN 1 ELSE -1);
sInc _ IF bbt.flags.gray THEN
IF (lineNum MOD grayHeightMod) = lastGray THEN grayBump ELSE grayWidth
ELSE srcInc;
IF sInc.easy AND dstInc.easy THEN {
srcAddr _ BitBltAddrInc[srcAddr, sInc];
dstAddr _ BitBltAddrInc[dstAddr, dstInc];
}
ELSE Recompute[bbt, sInc];
ENDLOOP;
};

DoSetup: PROC[bbt: PrincOps.BitBltTablePtr, goodDest: BitAddress]
	RETURNS[lineNum: CARDINAL] = {
IF bbt.flags.reserved # 0 OR bbt.reserved # 0 OR
bbt.src.reserved # 0 OR bbt.dst.reserved # 0 OR
bbt.width > LAST[NAT] OR bbt.height > LAST[NAT] THEN ERROR InvalidBitBltCall;

lastBBT _ bbt^;
goingForward _ bbt.flags.direction = forward;
srcFunc _ bbt.flags.srcFunc;
dstFunc _ bbt.flags.dstFunc;
srcAddr _ bbt.src;		-- true for either real source or gray
IF (isGray _ bbt.flags.gray) THEN {
grayParam _ LOOPHOLE[bbt.srcDesc];
IF grayParam.widthMinusOne # 0 OR grayParam.reserved # 0 OR
~goingForward OR ~bbt.flags.disjoint OR bbt.dstBpl < 0 THEN ERROR InvalidBitBltCall;
grayWidth.easy _ TRUE;
grayWidth.wVal _ grayParam.widthMinusOne+1;
grayWidth.bitVal _ grayWidth.wVal * bitsPerWord;
grayBump.easy _ TRUE;
grayBump.wVal _ -grayWidth.wVal*grayParam.heightMinusOne;
grayBump.bitVal _ grayBump.wVal * bitsPerWord;
}
ELSE {
srcI: INTEGER = LOOPHOLE[bbt.srcDesc];
IF srcI < 0 THEN srcInc.easy _ (-srcI MOD bitsPerWord) = 0
ELSE srcInc.easy _ (srcI MOD bitsPerWord) = 0;
srcInc.wVal _ IF srcInc.easy THEN srcI/bitsPerWord ELSE -1;
srcInc.bitVal _ srcI;
IF (goingForward AND (srcInc.bitVal < 0 OR bbt.dstBpl < 0)) OR
(~goingForward AND (srcInc.bitVal > 0 OR bbt.dstBpl > 0)) THEN
	ERROR InvalidBitBltCall;
};
IF bbt.dstBpl < 0 THEN dstInc.easy _ (-bbt.dstBpl MOD bitsPerWord) = 0
ELSE dstInc.easy _ (bbt.dstBpl MOD bitsPerWord) = 0;
dstInc.bitVal _ bbt.dstBpl;
dstInc.wVal _ IF dstInc.easy THEN bbt.dstBpl/bitsPerWord ELSE -1;

dstAddr _ bbt.dst;
IF goodDest.word # NIL THEN goodDstAddr _ goodDest;

IF isGray THEN lastGray _ IF goingForward THEN
grayParam.heightMinusOne - grayParam.yOffset
ELSE grayParam.yOffset;
lineNum _ IF goingForward THEN 0 ELSE bbt.height-1;
BEGIN
bitSkew: INTEGER = srcAddr.bit - dstAddr.bit;
finalDstInFirstLine: BitAddress _
BitBltAddrInc[bbt.dst, [wVal: -1, bitVal: bbt.width, easy: FALSE] ];
lMask _ LMask[dstAddr.bit];
rMask _ RMask[finalDstInFirstLine.bit];
skew _ IF bitSkew < 0 THEN bitsPerWord + bitSkew ELSE bitSkew;
dWidth _ (dstAddr.bit + bbt.width + bitsPerWord - 1)/bitsPerWord;
sWidth _ (srcAddr.bit + bbt.width + bitsPerWord - 1)/bitsPerWord;
isThin _ (dWidth = 1);
extraWordAtLeft _ extraWordAtRight _ FALSE;
SELECT TRUE FROM
sWidth > dWidth => extraWordAtLeft _ extraWordAtRight _ TRUE;
sWidth < dWidth, sWidth = 1 => NULL;
ENDCASE =>
IF bitSkew >= 0 THEN extraWordAtLeft _ TRUE
ELSE extraWordAtRight _ TRUE;
IF ~dstInc.easy AND dstInc.bitVal < 0 AND debugging THEN SIGNAL HardCase;
END;
};

BitBltAddrInc: PROC[base: BitAddress, offset: BitBltInc] RETURNS[ba: BitAddress] = {
IF offset.easy THEN {
ba.word _ LOOPHOLE[base.word + offset.wVal];
ba.bit _ base.bit;
}
ELSE {
add: LongNumber = LOOPHOLE[base.bit + offset.bitVal];
wordPart: LongNumber _ LOOPHOLE[DoubleShift[add, -logBitsPerWord]];
wordPart.hi _ add.hi;		-- makes negative if add was negative
ba.word _ LOOPHOLE[base.word + LOOPHOLE[wordPart, INT]];
ba.bit _ BITAND[add.lo, bitsPerWord-1];
};
};

Recompute: PROC[bbt: PrincOps.BitBltTablePtr, sInc: BitBltInc] = {
bitSkew: INTEGER;
finalDstAddrInLine: BitAddress;

srcAddr _ BitBltAddrInc[srcAddr,
[wVal: sInc.wVal, bitVal: sInc.bitVal, easy: sInc.easy] ];
dstAddr _ BitBltAddrInc[dstAddr,
[wVal: dstInc.wVal, bitVal: dstInc.bitVal, easy: dstInc.easy] ];

bitSkew _ srcAddr.bit - dstAddr.bit;
skew _ IF bitSkew < 0 THEN bitsPerWord + bitSkew ELSE bitSkew;
finalDstAddrInLine _ BitBltAddrInc[dstAddr, [wVal: -1, bitVal: bbt.width, easy: FALSE] ];
lMask _ LMask[dstAddr.bit];
rMask _ RMask[finalDstAddrInLine.bit];
dWidth _ (dstAddr.bit + bbt.width + bitsPerWord - 1)/bitsPerWord;
sWidth _ (srcAddr.bit + bbt.width + bitsPerWord - 1)/bitsPerWord;
isThin _ dWidth = 1;
extraWordAtLeft _ extraWordAtRight _ FALSE;
SELECT TRUE FROM
sWidth > dWidth => extraWordAtLeft _ extraWordAtRight _ TRUE;
sWidth < dWidth, sWidth = 1 => NULL;
ENDCASE =>
IF bitSkew >= 0 THEN extraWordAtLeft _ TRUE
ELSE extraWordAtRight _ TRUE;
};

RecomputeCheck: PROC[
bbt: PrincOps.BitBltTablePtr, goodDestBase: BitAddress, sInc: BitBltInc] = {
bitSkew: INTEGER;
finalDstAddrInLine: BitAddress;
srcAddr _ BitBltAddrInc[srcAddr, [wVal: sInc.wVal, bitVal: sInc.bitVal, easy: sInc.easy] ];
dstAddr _ BitBltAddrInc[dstAddr, [wVal: dstInc.wVal, bitVal: dstInc.bitVal, easy: dstInc.easy] ];
IF goodDestBase.word # NIL THEN goodDstAddr _ BitBltAddrInc[goodDstAddr,
[wVal: dstInc.wVal, bitVal: dstInc.bitVal, easy: dstInc.easy] ];

bitSkew _ srcAddr.bit - dstAddr.bit;
skew _ IF bitSkew < 0 THEN bitsPerWord - bitSkew ELSE bitSkew;
finalDstAddrInLine _ BitBltAddrInc[dstAddr, [wVal: -1, bitVal: bbt.width, easy: FALSE] ];
lMask _ LMask[dstAddr.bit];
rMask _ RMask[finalDstAddrInLine.bit];
dWidth _ (dstAddr.bit + bbt.width + bitsPerWord - 1)/bitsPerWord;
sWidth _ (srcAddr.bit + bbt.width + bitsPerWord - 1)/bitsPerWord;
isThin _ dWidth = 1;
extraWordAtLeft _ extraWordAtRight _ FALSE;
SELECT TRUE FROM
sWidth > dWidth => extraWordAtLeft _ extraWordAtRight _ TRUE;
sWidth < dWidth, sWidth = 1 => NULL;
ENDCASE =>
IF bitSkew >= 0 THEN extraWordAtLeft _ TRUE
ELSE extraWordAtRight _ TRUE;
};

BltOneLineForward: PROC = TRUSTED {
src: LONG POINTER TO WORD _ LOOPHOLE[srcAddr.word];
dst: LONG POINTER TO WORD _ LOOPHOLE[dstAddr.word];
longSrc, shiftedSrc: Basics.LongNumber;
dstValue, srcWord, curVal: WORD;
width: INTEGER _ dWidth;

longSrc.hi _ longSrc.lo _ src^;
src _ LOOPHOLE[src+1];
IF extraWordAtLeft THEN {	
longSrc.lo _ src^;
src _ LOOPHOLE[src+1];
};
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];

IF isThin THEN {
doubleMask: WORD = Basics.BITAND[lMask, rMask];
curVal _ Basics.BITAND[dst^, Basics.BITNOT[doubleMask]];
dstValue _ Basics.BITAND[dstValue, doubleMask];
dst^ _ Basics.BITOR[curVal, dstValue];
RETURN;
};

dstValue _ Basics.BITAND[dstValue, lMask];		-- at left side, so do left mask
curVal _ Basics.BITAND[dst^, BITNOT[lMask]];
dstValue _ Basics.BITOR[curVal, dstValue];

DO		-- store full words in this loop
dst^ _ dstValue;
dst _ LOOPHOLE[dst + 1];

longSrc _ Basics.SwapHalves[longSrc];		-- cheaper than shifting
IF width <=2 THEN EXIT;
longSrc.lo _ src^;
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];
src _ LOOPHOLE[src+1];
width _ width - 1;
ENDLOOP;

IF extraWordAtRight THEN longSrc.lo _ src^;
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];

curVal _ Basics.BITAND[dst^, Basics.BITNOT[rMask] ];
dstValue _ Basics.BITAND[dstValue, rMask];		-- at right side, so do right mask
dst^ _ Basics.BITOR[curVal, dstValue];
};

BltOneLineForwardCheck: PROC = TRUSTED {
src: LONG POINTER TO WORD _ LOOPHOLE[srcAddr.word];
dst: LONG POINTER TO WORD _ LOOPHOLE[dstAddr.word];
goodDst: LONG POINTER TO WORD _ LOOPHOLE[goodDstAddr.word];
longSrc, shiftedSrc: Basics.LongNumber;
dstValue, srcWord, curVal: WORD;
width: INTEGER _ dWidth;
first: BOOL _ TRUE;

longSrc.hi _ longSrc.lo _ src^;
src _ LOOPHOLE[src+1];
IF extraWordAtLeft THEN {	
longSrc.lo _ src^;
src _ LOOPHOLE[src+1];
};
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];

IF isThin THEN {
doubleMask: WORD = Basics.BITAND[lMask, rMask];
goodMaskedVal: WORD = Basics.BITAND[goodDst^, doubleMask];
dstValue _ Basics.BITAND[dstValue, doubleMask];
IF dstValue # goodMaskedVal THEN SIGNAL BadValueThin;
curVal _ Basics.BITAND[dst^, Basics.BITNOT[doubleMask]];
dst^ _ Basics.BITOR[curVal, dstValue];
RETURN;
};

DO		-- store full words in this loop
IF first THEN {
goodMaskedVal: WORD = Basics.BITAND[goodDst^, lMask];
dstValue _ Basics.BITAND[dstValue, lMask];		-- at left side, so do left mask
curVal _ Basics.BITAND[dst^, BITNOT[lMask]];
IF dstValue # goodMaskedVal THEN SIGNAL BadValueForward[$left];
dstValue _ Basics.BITOR[curVal, dstValue];
first _ FALSE;
}
ELSE IF dstValue # goodDst^ THEN SIGNAL BadValueForward[$middle];
dst^ _ dstValue;
dst _ LOOPHOLE[dst + 1];
goodDst _ LOOPHOLE[goodDst + 1];

longSrc _ Basics.SwapHalves[longSrc];		-- cheaper than shifting
IF width <=2 THEN EXIT;
longSrc.lo _ src^;
src _ LOOPHOLE[src+1];
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];
width _ width - 1;
ENDLOOP;

IF extraWordAtRight THEN longSrc.lo _ src^;
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];
BEGIN
goodMaskedVal: WORD = Basics.BITAND[goodDst^, rMask];
curVal _ Basics.BITAND[dst^, Basics.BITNOT[rMask] ];
dstValue _ Basics.BITAND[dstValue, rMask];		-- at right side, so do right mask
IF dstValue # goodMaskedVal THEN SIGNAL BadValueForward[$right];
dstValue _ Basics.BITOR[curVal, dstValue];
END;
dst^ _ dstValue;
};

BltOneLineForwardGray: PROC = TRUSTED {
src: LONG POINTER TO WORD _ LOOPHOLE[srcAddr.word];
dst: LONG POINTER TO WORD _ LOOPHOLE[dstAddr.word];
longSrc, shiftedSrc: Basics.LongNumber;
dstValue, srcWord, curVal: WORD;
width: INTEGER _ dWidth;
count: CARDINAL _ 0;

longSrc.hi _ longSrc.lo _ src^;
src _ GrayInc[src, count _ count + 1];
IF extraWordAtLeft THEN {	
longSrc.lo _ src^;
src _ GrayInc[src, count _ count + 1];
};
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];

IF isThin THEN {
doubleMask: WORD = Basics.BITAND[lMask, rMask];
curVal _ Basics.BITAND[dst^, Basics.BITNOT[doubleMask]];
dstValue _ Basics.BITAND[dstValue, doubleMask];
dst^ _ Basics.BITOR[curVal, dstValue];
RETURN;
};

dstValue _ Basics.BITAND[dstValue, lMask];		-- at left side, so do left mask
curVal _ Basics.BITAND[dst^, BITNOT[lMask]];
dstValue _ Basics.BITOR[curVal, dstValue];

DO		-- store full words in this loop
dst^ _ dstValue;
dst _ LOOPHOLE[dst + 1];

longSrc _ Basics.SwapHalves[longSrc];		-- cheaper than shifting
IF width <=2 THEN EXIT;
longSrc.lo _ src^;
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];
src _ GrayInc[src, count _ count + 1];
width _ width - 1;
ENDLOOP;

IF extraWordAtRight THEN longSrc.lo _ src^;
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];

curVal _ Basics.BITAND[dst^, Basics.BITNOT[rMask] ];
dstValue _ Basics.BITAND[dstValue, rMask];		-- at right side, so do right mask
dst^ _ Basics.BITOR[curVal, dstValue];
};

BltOneLineForwardGrayCheck: PROC = TRUSTED {
src: LONG POINTER TO WORD _ LOOPHOLE[srcAddr.word];
dst: LONG POINTER TO WORD _ LOOPHOLE[dstAddr.word];
goodDst: LONG POINTER TO WORD _ LOOPHOLE[goodDstAddr.word];
longSrc, shiftedSrc: Basics.LongNumber;
dstValue, srcWord, curVal: WORD;
width: INTEGER _ dWidth;
first: BOOL _ TRUE;
count: CARDINAL _ 0;

longSrc.hi _ longSrc.lo _ src^;
src _ GrayInc[src, count _ count + 1];
IF extraWordAtLeft THEN {	
longSrc.lo _ src^;
src _ GrayInc[src, count _ count + 1];
};
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];

IF isThin THEN {
doubleMask: WORD = Basics.BITAND[lMask, rMask];
goodMaskedVal: WORD = Basics.BITAND[goodDst^, doubleMask];
dstValue _ Basics.BITAND[dstValue, doubleMask];
IF dstValue # goodMaskedVal THEN SIGNAL BadValueThin;
curVal _ Basics.BITAND[dst^, Basics.BITNOT[doubleMask]];
dst^ _ Basics.BITOR[curVal, dstValue];
RETURN;
};

DO		-- store full words in this loop
IF first THEN {
goodMaskedVal: WORD = Basics.BITAND[goodDst^, lMask];
dstValue _ Basics.BITAND[dstValue, lMask];		-- at left side, so do left mask
curVal _ Basics.BITAND[dst^, BITNOT[lMask]];
IF dstValue # goodMaskedVal THEN SIGNAL BadValueForward[$left];
dstValue _ Basics.BITOR[curVal, dstValue];
first _ FALSE;
}
ELSE IF dstValue # goodDst^ THEN SIGNAL BadValueForward[$middle];
dst^ _ dstValue;
dst _ LOOPHOLE[dst + 1];
goodDst _ LOOPHOLE[goodDst + 1];

longSrc _ Basics.SwapHalves[longSrc];		-- cheaper than shifting
IF width <=2 THEN EXIT;
longSrc.lo _ src^;
src _ GrayInc[src, count _ count + 1];
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];
width _ width - 1;
ENDLOOP;
IF extraWordAtRight THEN longSrc.lo _ src^;
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];
BEGIN
goodMaskedVal: WORD = Basics.BITAND[goodDst^, rMask];
curVal _ Basics.BITAND[dst^, Basics.BITNOT[rMask] ];
dstValue _ Basics.BITAND[dstValue, rMask];		-- at right side, so do right mask
IF dstValue # goodMaskedVal THEN SIGNAL BadValueForward[$right];
dstValue _ Basics.BITOR[curVal, dstValue];
END;
dst^ _ dstValue;
};

BltOneLineBackward: PROC = TRUSTED {
src: LONG POINTER TO WORD _ LOOPHOLE[srcAddr.word + sWidth - 1];
dst: LONG POINTER TO WORD _ LOOPHOLE[dstAddr.word + dWidth - 1];
longSrc, shiftedSrc: Basics.LongNumber;
dstValue, srcWord, curVal: WORD;
width: INTEGER _ dWidth;

longSrc.hi _ longSrc.lo _ src^;
src _ LOOPHOLE[src-1];
IF extraWordAtRight THEN {
longSrc.hi _ src^;
src _ LOOPHOLE[src-1];
};
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];

IF isThin THEN {
doubleMask: WORD = Basics.BITAND[lMask, rMask];
curVal _ Basics.BITAND[dst^, Basics.BITNOT[doubleMask]];
dstValue _ Basics.BITAND[dstValue, doubleMask];
dst^ _ Basics.BITOR[curVal, dstValue];
RETURN;
};

dstValue _ Basics.BITAND[dstValue, rMask];		-- at right side, so do right mask
curVal _ Basics.BITAND[dst^, Basics.BITNOT[rMask] ];
dstValue _ Basics.BITOR[curVal, dstValue];

DO		-- store full words in this loop
dst^ _ dstValue;
dst _ LOOPHOLE[dst-1];

longSrc _ Basics.SwapHalves[longSrc];		-- cheaper than shifting
IF width <=2 THEN EXIT;
longSrc.hi _ src^;
src _ LOOPHOLE[src-1];
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];
width _ width - 1;
ENDLOOP;
IF extraWordAtLeft THEN longSrc.lo _ src^;
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];
dstValue _ Basics.BITAND[dstValue, lMask];		-- at left side, so do left mask
curVal _ Basics.BITAND[dst^, BITNOT[lMask]];
dst^ _ Basics.BITOR[curVal, dstValue];
};

BltOneLineBackwardCheck: PROC = TRUSTED {
src: LONG POINTER TO WORD _ LOOPHOLE[srcAddr.word + sWidth - 1];
dst: LONG POINTER TO WORD _ LOOPHOLE[dstAddr.word + dWidth - 1];
goodDst: LONG POINTER TO WORD _ LOOPHOLE[goodDstAddr.word + dWidth - 1];
longSrc, shiftedSrc: Basics.LongNumber;
dstValue, srcWord, curVal: WORD;
width: INTEGER _ dWidth;
first: BOOL _ TRUE;

longSrc.hi _ longSrc.lo _ src^;
src _ LOOPHOLE[src-1];
IF extraWordAtRight THEN {
longSrc.hi _ src^;
src _ LOOPHOLE[src-1];
};

[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];

IF isThin THEN {
doubleMask: WORD = Basics.BITAND[lMask, rMask];
goodMaskedVal: WORD = Basics.BITAND[goodDst^, doubleMask];
dstValue _ Basics.BITAND[dstValue, doubleMask];
IF dstValue # goodMaskedVal THEN SIGNAL BadValueThin;
curVal _ Basics.BITAND[dst^, Basics.BITNOT[doubleMask]];
dst^ _ Basics.BITOR[curVal, dstValue];
RETURN;
};

dstValue _ Basics.BITAND[dstValue, rMask];		-- at right side, so do right mask
curVal _ Basics.BITAND[dst^, Basics.BITNOT[rMask] ];

DO		-- store full words in this loop
IF first THEN {
goodMaskedVal: WORD = Basics.BITAND[goodDst^, rMask];
IF dstValue # goodMaskedVal THEN SIGNAL BadValueBackward[$right];
dstValue _ Basics.BITOR[curVal, dstValue];
first _ FALSE;
}
ELSE IF dstValue # goodDst^ THEN SIGNAL BadValueBackward[$middle];
dst^ _ dstValue;
dst _ LOOPHOLE[dst-1];
goodDst _ LOOPHOLE[goodDst-1];

longSrc _ Basics.SwapHalves[longSrc];		-- cheaper than shifting
IF width <=2 THEN EXIT;
longSrc.hi _ src^;
src _ LOOPHOLE[src-1];
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];
width _ width - 1;
ENDLOOP;

IF extraWordAtLeft THEN longSrc.lo _ src^;
[shiftedSrc, srcWord, dstValue] _ ComputeDstValue[longSrc, dst];

BEGIN
goodMaskedVal: WORD = Basics.BITAND[goodDst^, lMask];
curVal _ Basics.BITAND[dst^, BITNOT[lMask]];
dstValue _ Basics.BITAND[dstValue, lMask];		-- at left side, so do left mask
IF dstValue # goodMaskedVal THEN SIGNAL BadValueBackward[$left];
dstValue _ Basics.BITOR[curVal, dstValue];
END;
dst^ _ dstValue;
};

ComputeDstValue: PROC[longSrc: Basics.LongNumber, dst: LONG POINTER TO WORD]
	RETURNS[shiftedSrc: Basics.LongNumber, srcWord, dstValue: WORD] = {
shiftedSrc _ Basics.DoubleShiftLeft[longSrc, skew];
srcWord _ shiftedSrc.hi; 
IF srcFunc = complement THEN srcWord _ Basics.BITNOT[srcWord];
dstValue _ SELECT dstFunc FROM
null => srcWord,
and => Basics.BITAND[srcWord, dst^],
or => Basics.BITOR[srcWord, dst^],
xor =>Basics.BITXOR[srcWord, dst^],
ENDCASE => ERROR InvalidBitBltCall;
};

GrayInc: PROC[src: LONG POINTER TO WORD, count: INT]
	RETURNS[LONG POINTER TO WORD] = {
inc: INT;
IF grayWidth.wVal = 1 THEN RETURN[src]		-- special case
ELSE inc _ count MOD grayWidth.wVal;
RETURN[LOOPHOLE[src+inc]];
};

LMask: PROC[bitNum: [0..bitsPerWord)] RETURNS[WORD] = {
SELECT bitNum FROM
 0 => RETURN[177777B];
 1 => RETURN[ 77777B];
 2 => RETURN[ 37777B];
 3 => RETURN[ 17777B];
 4 => RETURN[  7777B];
 5 => RETURN[  3777B];
 6 => RETURN[  1777B];
 7 => RETURN[   777B];
 8 => RETURN[   377B];
 9 => RETURN[   177B];
10 => RETURN[    77B];
11 => RETURN[    37B];
12 => RETURN[    17B];
13 => RETURN[     7B];
14 => RETURN[     3B];
15 => RETURN[     1B];
ENDCASE => ERROR InvalidBitBltCall;
};

RMask: PROC[bitNum: [0..bitsPerWord)] RETURNS[WORD] = {
SELECT bitNum FROM
 0 => RETURN[177777B];		-- really bit 16
ENDCASE => RETURN[BITNOT[LMask[bitNum]] ];
};

END.

XBitBltOpsImpl.mesa
Copyright (C) 1986 by Xerox Corporation.  All rights reserved.
Willie-Sue, September 11, 1986 3:27:06 pm PDT

Cedar code to implement the BitBlt operation as defined (almost) by PrincOps
dWidth & sWidth differ by ar most +/-1
dWidth > 2 => left partial, dWidth-2 full words, and right partial
dWidth = 2 => left partial, right partial only
dWidth = 1 => entire destination within one word - special case as both masks need to be applied at the same time
If sWidth = dWidth+1, an extra source word must be fetched at both ends.
If sWidth = dWidth-1 or sWidth = 1, no extra source words need be fetched.
If sWidth = dWidth # 1, an extra source word must be fetched at one end:
if src.bit mod 20 > dst.bit mod 20 then left else right
ENABLE UNWIND, ABORTED => NULL;
ENABLE UNWIND, ABORTED => NULL;
check for legality
(~bbt.flags.gray AND LOOPHOLE[bbt.srcDesc, INTEGER] = 0) OR  -- bbt.dstBpl = 0 OR
more checking

checking for thin case, setting up masks, widths for line
what we really want here is arithemtic right shift, but alas, we'll have to fake it
we know that base.bit + offset.bitVal is no more than 16 bits
IF add.hi < 0 THEN wordPart.hi _ 177777B;
either srcBpl or dstBpl was not a multiple of bitsPerWord; recompute masks for this line

either srcBpl or dstBpl was not a multiple of bitsPerWord; recompute masks for this line






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