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Save 1 cycle per line in the PEA fast-path for odd-aligned blits

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Lucas Scharenbroich 2022-02-02 14:30:48 -06:00
parent 108335e90a
commit 5f492fd557
1 changed files with 11 additions and 10 deletions
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21
src/blitter/Template.s
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@ -546,18 +546,11 @@ entry_jmp jmp $0100
; an amortized 4-cycles per line to set the entry point break
right_odd bit #$000B ; Check the bottom nibble to quickly identify a PEA instruction
beq r_is_pea ; This costs 6 cycles in the fast-path
bne r_is_not_pea ; This costs 5 cycles in the fast-path
bit #$0040 ; Check bit 6 to distinguish between JMP and all of the LDA variants
bne r_is_jmp
long_1 stal *+4-base ; Everything else is a two-byte LDA opcode + PHA
dfb $00,$00
bra r_jmp_rtn
r_is_pea xba ; fast code for PEA
xba ; fast code for PEA
r_jmp_rtn sep #$20 ; shared return code path by all methods
pha
two_byte_rtn pha
rep #$61 ; Clear Carry, Overflow and M bits #$20
odd_entry jmp $0100 ; unconditionally jump into the "next" instruction in the
; code field. This is OK, even if the entry point was the
@ -569,6 +562,14 @@ odd_entry jmp $0100 ; unconditionally jump into
; code field is page-aligned, only the low byte needs to
; be updated when the scroll position changes
r_is_not_pea bit #$0040 ; Check bit 6 to distinguish between JMP and all of the LDA variants
bne r_is_jmp
long_1 stal *+6-base ; Everything else is a two-byte LDA opcode + PHA
sep #$20 ; Lift 8-bit mode here to save a cycle in the LDA
dfb $00,$00
bra two_byte_rtn
r_is_jmp sep #$41 ; Set the C and V flags which tells a snippet to push only the low byte
long_2 ldal entry_jmp+1-base
long_3 stal *+5-base