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entropy: update comments

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Vince Weaver 2018-05-28 01:30:12 -04:00
parent 09c3e7d70b
commit 8df4d4c3e3
1 changed files with 18 additions and 31 deletions
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45
two-liners/entropy.s
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@ -27,11 +27,6 @@
; zero page locations
HGR_SHAPE = $1A
TEMP1_EXP = $93
TEMP1_HO = $94
TEMP1_MOH = $95
TEMP1_MO = $96
TEMP1_LO = $97
FAC_EXP = $9D
FAC_HO = $9E
FAC_MOH = $9F
@ -44,7 +39,6 @@ RND_MOH = $CB
RND_MO = $CC
RND_LO = $CD
RND_SGN = $CE
HGR_SCALE = $E7
HGR_ROTATION = $F9
EPOS = $FC
@ -53,7 +47,6 @@ XPOSH = $FE
YPOS = $FF
; ROM calls
SNGFLT = $E301
CONINT = $E6FB
FMULT = $E97F
MUL10 = $EA39
@ -64,8 +57,7 @@ RND = $EFAE
HGR2 = $F3D8
HPOSN = $F411
XDRAW0 = $F65D
; ROM constants
TEN = $EA50
entropy:
@ -78,8 +70,7 @@ entropy:
eloop:
lda #4 ; FOR Y=4 to 189 STEP 6
; sta YPOS
pha
pha ; YPOS stored on stack
yloop:
lda #4 ; FOR X=4 to 278 STEP 6
sta XPOS
@ -93,11 +84,6 @@ xloop:
; Equivalent to IF RND(1)<E THEN SCALE=RND(1)*E*20+1
; ELSE SCALE=1
; E=.08 80% of time less, so 0 + (0 to .08)*20 = 0 to 1.6
; 80% of time 1 to 2.6, 20% of time 2 to 3.6
; E=.15 65% 0+(0 to .15)*20 = 0 to 3
; 65% 1 to 4, 45% 2 to 5
; Note the Apple II generates a seed based on keypresses
; but by default RND is never seeded from there.
; Someone actually wrote an entire academic paper complaining about
@ -107,37 +93,38 @@ xloop:
; on the Apple II", Behavior Research Methods, Instruments,
; & Computers, 1987, 19 (4), 397-399.
; put random value in FAC
; get random value in FAC
ldx #1 ; RND(1), Force 1
jsr RND+6 ; we skip passing the argument
; in FAC as that would be a pain
; as a floating point value
; as that would be a pain
; Compare to E
jsr MUL10 ; EPOS is *100, so multiply*100 first
jsr MUL10
jsr MUL10 ; EPOS is E*100
jsr MUL10 ; so multiply rand*100 before compare
jsr CONINT ; convert to int
; X is now RND(1)*100
cpx EPOS
ldx #1 ; the boring case
bcs done ; branch if less than EPOS
cpx EPOS ; compare E*100 to RND*100
ldx #1 ; load 1 into X (this is clever)
bcs done ; if EPOS>=RND then SCALE=1, skip ahead
; SCALE=RND(1)*E*20+1
; EPOS is E*100, so RND(1)*(EPOS/10)*2+1
; is EPOS/4 close enough?
; put random value in FAC
; ldx #1 ; RND(1), Force 1
jsr RND+6 ; we skip passing the argument
; in FAC as that would be a pain
; ldx #1 ; RND(1), Force 1, this set from earlier
jsr RND+6 ; skip arg parsing in RND
lda EPOS
jsr FLOAT ; convert value in A to float in FAC
jsr DIV10 ; FAC=FAC/10
ldy #>RND_EXP
ldy #>RND_EXP ; point (Y,A) to RND value
lda #<RND_EXP
jsr FMULT ; multiply FAC by (Y,A)
inc FAC_EXP ; multiply by 2