; AltoByteBlt.asm -- Routine to move a block of bytes quickly. ; E. A. Taft / February, 1976 ; Copyright Xerox Corporation 1979 .ent ByteBlt .srel ByteBlt: .ByteBlt .nrel ; Frame offsets Temp=2. DstAdr=4. ; Arguments start here DstByte=5. SrcAdr=6. SrcByte=7. ByteCount=8. FrameSize=9. ; BCPL runtime getframe=370 storeargs=367 return=366 ; ByteBlt(DstAdr,DstByte,SrcAdr,SrcByte,ByteCount) ; Transfer a block of bytes according to arguments: ; DstAdr Word address of first destination byte ; DstByte Offset of first destination byte ; SrcAdr Word address of first source byte ; SrcByte Offset of first source byte ; ByteCount Number of bytes to transfer .ByteBlt: sta 3 1 2 ; Standard BCPL entry sequence jsr @getframe FrameSize jsr @storeargs ; Reduce the byte indices to the range [0,1] lda 0 SrcByte 2 ; Get source byte offset movzr 0 0 ; Compute word offset, remainder lda 3 SrcAdr 2 ; Update source address add 0 3 sta 3 SrcAdr 2 subcl 0 0 ; Leftover bytes (0 or 1) sta 0 SrcByte 2 lda 1 DstByte 2 ; Get destination byte offset movzr 1 1 ; Compute word offset, remainder lda 3 DstAdr 2 ; Update destination address add 1 3 sta 3 DstAdr 2 subcl 1 1 ; Leftover bytes (0 or 1) sta 1 DstByte 2 ; Test for small number of bytes to move lda 3 ByteCount 2 ; Get byte count negor 3 3 szr ; 4 or fewer bytes? comzr 3 3 snr jmp bytbl8 ; Yes, move them the slow way ; See whether source and destination byte positions are in phase se 0 1 ; In phase? jmp bytbl5 ; No ; Bytes are in phase, do move with blt sz 0 0 ; Starting with even byte? jsr MoveByte ; No, move one byte manually lda 3 ByteCount 2 ; Get byte count movzr 3 3 ; Compute full words to move subcl 0 0 ; Leftover bytes (0 or 1) sta 0 ByteCount 2 ; Update byte count lda 0 SrcAdr 2 ; Get first source address add 3 0 ; Update it sta 0 SrcAdr 2 lda 1 DstAdr 2 ; Get first destination address add 3 1 ; Update it sta 1 DstAdr 2 adc 3 0 ; Compute first source address -1 neg 1 1 ; Compute last dest adr for blt com 1 1 neg 3 3 ; Negate word count for blt blt ; Blast away jmp bytbl8 ; Handle leftover bytes ; Bytes are not in phase, do the transfer one word at a time bytbl5: sz 1 1 ; Destination on even byte? jsr MoveByte ; No, move a byte to make it be lda 1 ByteCount 2 ; Get byte count movzr 1 1 ; Convert to word count subcl 0 0 ; Leftover bytes (0 or 1) sta 0 ByteCount 2 ; Update byte count movzr 1 1 szc ; Compute word count/2 inc 1 1 ; Round doubleword count up sta 1 Temp 2 ; Store for loop lda 3 c377 ; Right byte mask for loop lda 0 @SrcAdr 2 ; Get first source byte (odd) and 3 0 ; Put zero in lh mov 0 1 szc ; Check remainder from count/2 jmp bytbl7 ; One leftover word ; Main loop -- transfers 4 bytes on each iteration. ; Here we have a leftover byte in rh of 0, zero in lh. bytbl6: isz SrcAdr 2 ; Increment source address lda 1 @SrcAdr 2 ; Get next source word add 1 0 ; Ac0 _ new lh , new rh+leftover and 3 1 ; Ac1 _ 0 , new rh subs 1 0 ; Ac0 _ leftover , new lh sta 0 @DstAdr 2 ; Store destination word isz DstAdr 2 ; Increment destination address ; Here we have a leftover byte in rh of 1, zero in lh. bytbl7: isz SrcAdr 2 ; Increment source address lda 0 @SrcAdr 2 ; Get next source word add 0 1 ; Ac1 _ new lh , new rh+leftover and 3 0 ; Ac0 _ 0 , new rh subs 0 1 ; Ac1 _ leftover , new lh sta 1 @DstAdr 2 ; Store destination word isz DstAdr 2 ; Increment destination address dsz Temp 2 ; Test doubleword count jmp bytbl6 ; More words to move ; Do leftover bytes (if any) the slow way bytbl8: lda 0 ByteCount 2 ; Check byte count snz 0 0 jsr @return ; No more, return jsr MoveByte ; More, transfer one byte jmp .-1 ; Repeat til MoveByte returns ; Internal routine to transfer one byte from source to destination. ; Returns to caller+1 if there are still more bytes to transfer. ; Executes BCPL return (returns to caller of ByteBlt) if no more. ; Updates all state in the frame of the caller (ByteBlt). ; Clobbers the frame Temp word MoveByte: sta 3 Temp 2 ; Save return lda 0 @SrcAdr 2 ; Get word containing source byte dsz SrcByte 2 ; Check source byte position jmp getevn ; Even ; Getting odd byte isz SrcAdr 2 ; Increment source address jmp movby1 ; Getting even byte getevn: movs 0 0 ; Swap byte to right half mkone 1 1 ; Fix up the byte position sta 1 SrcByte 2 movby1: lda 3 c377 ; Get byte mask lda 1 @DstAdr 2 ; Existing contents of dest word dsz DstByte 2 ; Check destination byte position jmp putevn ; Go store even byte ; Putting odd byte and 3 0 ; Mask out garbage, leave in rh movs 3 3 ; Make left half mask and 3 1 ; Retain lh of existing word add 1 0 ; Insert new byte in right half sta 0 @DstAdr 2 ; Store updated dest word isz DstAdr 2 ; Increment dest address jmp movby2 ; Go finish up ; Putting even byte putevn: ands 3 0 ; Mask out garbage, leave in lh and 3 1 ; Retain rh of existing word add 1 0 ; Insert new byte in left half sta 0 @DstAdr 2 ; Store updated dest word mkone 1 1 ; Fix up the byte position sta 1 DstByte 2 movby2: dsz ByteCount 2 ; Decrement remaining byte count jmp @Temp 2 ; More to do, return to ByteBlt jsr @return ; Exhausted, return from ByteBlt c377: 377 .end