Apple-2-SW
/
Applecorn
mirror of https://github.com/bobbimanners/Applecorn.git
1
0
Fork 0
Code Issues Projects Releases Wiki Activity

SHR: Handle -ve Y coordinates before clip

This commit is contained in:
Bobbi Webber-Manners 2023-01-05 18:40:20 -05:00
parent a4add222b9
commit 837e42e101
2 changed files with 34 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

BIN
applecorn.po
View File

Binary file not shown.

35
mainmem.shr.s
View File

@ -686,7 +686,8 @@ SHRCOORD PHP ; Disable interrupts
STA A1L ; Result in A1L/H
* Y-coordinate in SHRVDUQ+7,+8 1024*25/128=200
:Y LDA SHRVDUQ+7
LDA SHRVDUQ+7
BMI :MINUS
ASL ; *2
ADC SHRVDUQ+7 ; *3
ASL ; *6
@ -714,6 +715,38 @@ SHRCOORD PHP ; Disable interrupts
PLP ; Normal service resumed
RTS
:MINUS MX %00 ; Tell Merlin we are 16 bit
EOR #$FFFF ; Negate
INC A
ASL ; *2
ADC SHRVDUQ+7 ; *3
ASL ; *6
ASL ; *12
ASL ; *24
ADC SHRVDUQ+7 ; *25
* Clever speedup trick thanks to Kent Dickey @ A2Infinitum
* now we have valid data in acc[15:7], and we want to shift right 7 bits to
* get acc[8:0] as the valid bits. If we left shift one bit and xba,
* we get acc[7:0] in the proper bits, so we just have to bring the bit we
* just shifted out back
* See: https://apple2infinitum.slack.com/archives/CA8AT5886/p1628877444215300
* for code on how to shift left 7 bits
ASL ;
AND #$FF00 ; Mask bits
ADC #0 ; Add in carry (9th bit)
XBA ; Clever trick: fewer shifts
EOR #$FFFF ; Negate
INC A
STA A2L ; Into A2L/H
SEC ; Back to emulation mode
XCE
MX %11 ; Tell Merlin
PLP ; Normal service resumed
RTS
* Table of addresses of SHR rows (in reverse order)
SHRROWSL DB <$9c60