mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-12-28 09:30:41 +00:00
| .. | ||
| docs | ||
| dump.bas | ||
| EA.PT3 | ||
| empty.dsk | ||
| gr_fast_clear.s | ||
| HELLO | ||
| hello.bas | ||
| interrupt_handler.s | ||
| Makefile | ||
| mockingboard_a.s | ||
| pt3_dumper.s | ||
| pt3_lib.s | ||
| pt3_player.dsk | ||
| pt3_player.s | ||
| pt3_timer.s | ||
| qkumba_rts.s | ||
| README.pt3_player | ||
| song_list.inc | ||
| SR.PT3 | ||
| text_print.s | ||
| TODO | ||
| VC.PT3 | ||
| zp.inc | ||
PT3_player
ASR = CMP #$80 / ROR
Notes:
signed 8-bit comparison
see http://6502.org/tutorials/compare_beyond.html#2.2
SEC ; prepare carry for SBC
SBC NUM ; A-NUM
BVC LABEL ; if V is 0, N eor V = N, otherwise N eor V = N eor 1
EOR #$80 ; A = A eor $80, and N = N eor 1
LABEL
If the N flag is 1, then A (signed) < NUM (signed) and BMI will branch
If the N flag is 0, then A (signed) >= NUM (signed) and BPL will branch