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CALCMAND.ASM
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Assembly Source File
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1990-09-10
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25KB
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841 lines
; CALCMAND.ASM - Mandelbrot/Julia Set calculation Routines
; This module runs as part of an overlay with calcfrac.c.
; It must not be called from anywhere other than calcfrac.
; The routines in this code perform Mandelbrot and Julia set
; calculations using 32-bit integer math as opposed to the
; "traditional" floating-point approach.
; This code relies on several tricks to run as quickly as it does.
; One can fake floating point arithmetic by using integer
; arithmetic and keeping track of the implied decimal point
; if things are reasonable -- and in this case, they are.
; I replaced code that looked like: z = x*y with code that
; looks like:
; ix = x * ifudge (outside the loops)
; iy = y * ifudge
; ....
; iz = (ix * iy) / ifudge (inside the loops)
; (and keep remembering that all the integers are "ifudged" bigger)
; The 386 has native 32-bit integer arithmetic, and (briefly) keeps
; 64-bit values around after 32-bit multiplies. If the result is
; divided down right away, you've got 64-bit arithmetic. You just
; have to ensure that the result after the divide is <= 32 bits long.
; CPUs predating the 386 have to emulate 32-bit arithmetic using
; 16-bit arithmetic, which is significantly slower.
; Dividing is slow -- but shifting is fast, and we can select our
; "fudge factor" to be a power of two, permitting us to use that
; method instead. In addition, the 386 can perform 32-bit wide
; shifting -- and even 64-bit shifts with the following logic:
; shdr eax,edx,cl
; shr edx,cl
; so we make sure that our "fudge factor" is a power of 2 and shift
; it down that way.
; Calcmand is hardcoded for a fudge factor of 2**29.
; Bert Tyler
; required for compatibility if Turbo ASM
IFDEF ??version
MASM51
QUIRKS
ENDIF
.MODEL medium,c
DGROUP group _DATA,_DATA2
.8086
; these must NOT be in any segment!!
; this get's rid of TURBO-C fixup errors
extrn keypressed:far ; this routine is in 'general.asm'
extrn getakey:far ; this routine is in 'general.asm'
extrn iplot_orbit:far ; this routine is in 'calcfrac.c'
extrn scrub_orbit:far ; this routine is in 'calcfrac.c'
_DATA2 segment DWORD PUBLIC 'DATA'
FUDGEFACTOR equ 29 ; default (non-potential) fudgefactor
; ************************ External variables *****************************
extrn fractype:word ; == 0 if Mandelbrot set, else Julia
extrn inside:word ; "inside" color, normally 1 (blue)
extrn creal:dword, cimag:dword ; Julia Set Constant
extrn delmin:dword ; min increment - precision required
extrn maxit:word ; maximum iterations
extrn lm:dword ; magnitude bailout limit
extrn row:word, col:word ; current pixel to calc
extrn color:word ; color calculated for the pixel
extrn reset_periodicity:word ; nonzero if to be reset
extrn kbdcount:word ; keyboard counter
extrn cpu:word ; cpu type: 86, 186, 286, or 386
extrn show_orbit:word ; "show-orbit" flag
extrn orbit_ptr:word ; "orbit pointer" flag
extrn periodicitycheck:word ; no periodicity if zero
public linitx,linity ; caller sets these
public savedmask ; caller sets this
; ************************ Internal variables *****************************
align 4
x dd 0 ; temp value: x
y dd 0 ; temp value: y
absx dd 0 ; temp value: abs(x)
linitx dd 0 ; initial value, set by calcfrac
linity dd 0 ; initial value, set by calcfrac
savedmask dd 0 ; saved values mask
savedx dd 0 ; saved values of X and Y iterations
savedy dd 0 ; (for periodicity checks)
k dw 0 ; iteration countdown counter
oldcolor dw 0 ; prior pixel's escape time k value
savedand dw 0 ; AND value for periodicity checks
savedincr dw 0 ; flag for incrementing AND value
period db 0 ; periodicity, if in the lake
_DATA2 ends
.CODE
; ***************** Function calcmandasm() **********************************
public calcmandasm
calcmandasm proc uses di si
sub ax,ax ; clear ax
cmp periodicitycheck,ax ; periodicity checking disabled?
je initoldcolor ; yup, set oldcolor 0 to disable it
cmp reset_periodicity,ax ; periodicity reset?
je short initparms ; inherit oldcolor from prior invocation
mov ax,maxit ; yup. reset oldcolor to maxit-250
sub ax,250 ; (avoids slowness at high maxits)
initoldcolor:
mov oldcolor,ax ; reset oldcolor
initparms:
mov ax,word ptr creal ; initialize x == creal
mov dx,word ptr creal+2 ; ...
mov word ptr x,ax ; ...
mov word ptr x+2,dx ; ...
mov ax,word ptr cimag ; initialize y == cimag
mov dx,word ptr cimag+2 ; ...
mov word ptr y,ax ; ...
mov word ptr y+2,dx ; ...
mov ax,maxit ; setup k = maxit
inc ax ; (+ 1)
mov k,ax ; (decrementing to 0 is faster)
cmp fractype,1 ; julia or mandelbrot set?
je short dojulia ; julia set - go there
; (Tim wants this code changed so that, for the Mandelbrot,
; Z(1) = (x + iy) + (a + ib). Affects only "fudged" Mandelbrots.
; (for the "normal" case, a = b = 0, and this works, too)
; cmp word ptr x,0 ; Mandelbrot shortcut:
; jne short doeither ; if creal = cimag = 0,
; cmp word ptr x+2,0 ; the first iteration can be emulated.
; jne short doeither ; ...
; cmp word ptr y,0 ; ...
; jne short doeither ; ...
; cmp word ptr y+2,0 ; ...
; jne short doeither ; ...
; dec k ; we know the first iteration passed
; mov dx,word ptr linitx+2 ; copy x = linitx
; mov ax,word ptr linitx ; ...
; mov word ptr x+2,dx ; ...
; mov word ptr x,ax ; ...
; mov dx,word ptr linity+2 ; copy y = linity
; mov ax,word ptr linity ; ...
; mov word ptr y+2,dx ; ...
; mov word ptr y,ax ; ...
dec k ; we know the first iteration passed
mov dx,word ptr linitx+2 ; add x += linitx
mov ax,word ptr linitx ; ...
add word ptr x,ax ; ...
adc word ptr x+2,dx ; ...
mov dx,word ptr linity+2 ; add y += linity
mov ax,word ptr linity ; ...
add word ptr y,ax ; ...
adc word ptr y+2,dx ; ...
jmp short doeither ; branch around the julia switch
dojulia: ; Julia Set initialization
; "fudge" Mandelbrot start-up values
mov ax,word ptr x ; switch x with linitx
mov dx,word ptr x+2 ; ...
mov bx,word ptr linitx ; ...
mov cx,word ptr linitx+2 ; ...
mov word ptr x,bx ; ...
mov word ptr x+2,cx ; ...
mov word ptr linitx,ax ; ...
mov word ptr linitx+2,dx ; ...
mov ax,word ptr y ; switch y with linity
mov dx,word ptr y+2 ; ...
mov bx,word ptr linity ; ...
mov cx,word ptr linity+2 ; ...
mov word ptr y,bx ; ...
mov word ptr y+2,cx ; ...
mov word ptr linity,ax ; ...
mov word ptr linity+2,dx ; ...
doeither: ; common Mandelbrot, Julia set code
mov period,0 ; claim periodicity of 1
mov savedand,1 ; initial periodicity check
mov savedincr,1 ; flag for incrementing periodicity
mov word ptr savedx+2,0ffffh; impossible value of "old" x
mov word ptr savedy+2,0ffffh; impossible value of "old" y
mov orbit_ptr,0 ; clear orbits
dec kbdcount ; decrement the keyboard counter
jns short nokey ; skip keyboard test if still positive
mov kbdcount,10 ; stuff in a low kbd count
cmp show_orbit,0 ; are we showing orbits?
jne quickkbd ; yup. leave it that way.
mov kbdcount,5000 ; else, stuff an appropriate count val
cmp cpu,386 ; ("appropriate" to the CPU)
je short quickkbd ; ...
cmp word ptr delmin+2,1 ; is 16-bit math good enough?
ja quickkbd ; yes. test less often
mov kbdcount,500 ; no. test more often
quickkbd:
call far ptr keypressed ; has a key been pressed?
cmp ax,0 ; ...
je nokey ; nope. proceed
cmp ax,'o' ; orbit toggle hit?
je orbitkey ; yup. show orbits
cmp ax,'O' ; orbit toggle hit?
jne keyhit ; nope. normal key.
orbitkey:
call far ptr getakey ; read the key for real
mov ax,1 ; reset orbittoggle = 1 - orbittoggle
sub ax,show_orbit ; ...
mov show_orbit,ax ; ...
mov kbdcount,10 ; adjust the keyboard
jmp short nokey ; pretend no key was hit
keyhit: mov ax,-1 ; return with -1
mov color,ax ; set color to -1
ret ; bail out!
noke