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Adjust rounding, loop exits

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Still slight differences between positive and negative Y halves
Not sure what's wrong
This commit is contained in:
Brooke Vibber 2023-01-28 12:07:42 -08:00
parent b6ddc0d50e
commit 76715a6151
1 changed files with 39 additions and 32 deletions
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71
mandel.s
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@ -359,48 +359,38 @@ positive_result:
.macro round16 arg .macro round16 arg
; Round top 16 bits of 32-bit fixed-point number in-place ; Round top 16 bits of 32-bit fixed-point number in-place
.local zero
.local one
.local positive .local positive
.local negative .local negative
.local neg2 .local increment
.local next .local next
; no round - 5 cycles ; positive input:
; round pos, no carry - 17 ; 0 rounds down, no change - 10 cyc
; round pos, carry - 22 ; 1 rounds up, add one - 17-22 cyc
; round neg, no carry - 23 ; negative input:
; round neg, carry - 28 ; 0 rounds up, add one - 19-24 cyc
; average = 5 / 2 + (17 + 22 + 23 + 28) / 8 ; 1 rounds down, no change - 10 cyc
; = 5 / 2 + 90 / 8
; = 2.5 + 11.25 = 13.75 cycles average on evenly distributed input
lda arg + 1 ; 3 cyc
bpl zero ; 2 cyc
one:
; check sign bit ; check sign bit
lda arg + 3 ; 3 cyc lda arg + 3 ; 3 cyc
bpl positive ; 2 cyc bpl positive ; 2 cyc
negative: negative:
lda arg + 2 ; 3 cyc ; check 16th bit down
beq neg2 ; 2 cyc lda arg + 1 ; 3 cyc
bmi next ; 2 cyc
dec arg + 2 ; 5 cyc bpl increment ; 2 cyc
jmp next ; 3 cyc
neg2:
dec arg + 2 ; 5 cyc
dec arg + 3 ; 5 cyc
jmp next ; 3 cyc
positive: positive:
; check 16th bit down
lda arg + 1 ; 3 cyc
bpl next ; 2 cyc
increment:
inc arg + 2 ; 5 cyc inc arg + 2 ; 5 cyc
bne next ; 2 cyc bne next ; 2 cyc
inc arg + 3 ; 5 cyc inc arg + 3 ; 5 cyc
zero:
next: next:
.endmacro .endmacro
@ -435,17 +425,34 @@ loop:
keep_going: keep_going:
.macro quick_exit arg, max .macro quick_exit arg, max
.local keep_going .local positive
.local keep_going2 .local negative
.local nope_out
.local first_equal
.local all_done
; check sign bit
lda arg + 1 lda arg + 1
bmi negative
positive:
cmp #((max) << 4) cmp #((max) << 4)
bmi keep_going bmi all_done ; 'less than'
rts rts
keep_going:
negative:
cmp #(256 - ((max) << 4)) cmp #(256 - ((max) << 4))
bpl keep_going2 beq first_equal ; 'equal' on first byte
bpl all_done ; 'greater than'
nope_out:
rts rts
keep_going2:
first_equal:
lda arg
beq nope_out ; 2nd byte 0 shows it's really 'equal'
all_done:
.endmacro .endmacro
; 4.12: (-8 .. +7.9) ; 4.12: (-8 .. +7.9)