; 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

; 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
; 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 realcolor:word ; color before inside,etc adjustments

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 dotmode:word

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
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

FRAME MACRO regs
push bp
mov bp, sp
IRP reg,
push reg
ENDM
ENDM

UNFRAME MACRO regs
IRP reg,
pop reg
ENDM
pop bp
ENDM

calcmandasm proc
FRAME ; std frame, for TC++ overlays
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)
cmp word ptr delmin+2,1 ; is 16-bit math good enough?
ja kbddiskadj ; yes. test less often
mov kbdcount,500 ; no. test more often
cmp dotmode,11 ; disk video?
jne quickkbd ; no, leave as is
shr kbdcount,1 ; yes, reduce count
shr kbdcount,1 ; ...
quickkbd:
call far ptr keypressed ; has a key been pressed?
cmp ax,0 ; ...
je nokey ; nope. proceed
mov kbdcount,0 ; make sure it goes negative again
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 ; ...
jmp short nokey ; pretend no key was hit
keyhit: mov ax,-1 ; return with -1
mov color,ax ; set color to -1
UNFRAME ; pop stack frame
ret ; bail out!

nokey:
cmp show_orbit,0 ; is orbiting on?
jne no16bitcode ; yup. slow down.
cmp cpu,386 ; are we on a 386?
je short code386bit ; YAY!! 386-class speed!
cmp word ptr delmin+2,1 ; OK, we're desperate. 16 bits OK?
ja yes16bitcode ; YAY! 16-bit speed!
no16bitcode:
call near ptr code32bit ; BOO!! nap time. Full 32 bit math
jmp kloopend ; bypass the 386-specific code.
yes16bitcode:
call near ptr code16bit ; invoke the 16-bit version
jmp kloopend ; bypass the 386-specific code.

.386 ; 386-specific code starts here

code386bit:
cmp word ptr delmin+2,3 ; is 16-bit math good enough?
jbe code386_32 ; nope, go do 32 bit stuff
IFDEF ??version
jmp code386_32 ; TASM screws up IMUL EBX,EBX!!
ENDIF

; 16 bit on 386, now we are really gonna move
movsx esi,word ptr x+2 ; use SI for X
movsx edi,word ptr y+2 ; use DI for Y
push ebp
mov ebp,-1
shl ebp,FUDGEFACTOR-1
mov cx,FUDGEFACTOR-16

mov ebx,esi ; compute (x * x)
imul ebx,ebx ; ...
test ebx,ebp ; say, did we overflow?
jnz short end386_16 ; (oops. We done.)
shr ebx,cl ; get result down to 16 bits

mov edx,edi ; compute (y * y)
imul edx,edx ; ...
test edx,ebp ; say, did we overflow?
jnz short end386_16 ; (oops. We done.)
shr edx,cl ; get result down to 16 bits

mov ax,bx ; compute (x*x - y*y) / fudge
sub bx,dx ; for the next iteration

add ax,dx ; compute (x*x + y*y) / fudge

cmp ax,word ptr lm+2 ; while (xx+yy < lm)
jae short end386_16 ; ...

imul edi,esi ; compute (y * x)
shl edi,1 ; ( * 2 / fudge)
sar edi,cl
add di,word ptr linity+2 ; (2*y*x) / fudge + linity
movsx edi,di ; save as y

add bx,word ptr linitx+2 ; (from above) (x*x - y*y)/fudge + linitx
movsx esi,bx ; save as x

mov ax,oldcolor ; recall the old color
cmp ax,k ; check it against this iter
jge short chkpd386_16 ; yup. do periodicity check.
nonmax386_16:
dec k ; while (k < maxit)
jnz short kloop386_16 ; try, try again
end386_16:
pop ebp
jmp kloopend ; we done

chkpd386_16:
mov ax,k ; set up to test for save-time
test ax,savedand ; save on 0, check on anything else
jz short chksv386_16 ; time to save a new "old" value
mov ax,si ; load up x
xor ax,word ptr savedx+2 ; does X match?
test ax,word ptr savedmask+2 ; truncate to appropriate precision
jne short nonmax386_16 ; nope. forget it.
mov ax,di ; now test y
xor ax,word ptr savedy+2 ; does Y match?
test ax,word ptr savedmask+2 ; truncate to appropriate precision
jne short nonmax386_16 ; nope. forget it.
mov period,1 ; note that we have found periodicity
mov k,0 ; pretend maxit reached
jmp short end386_16
chksv386_16:
mov word ptr savedx+2,si ; save x
mov word ptr savedy+2,di ; save y
dec savedincr ; time to change the periodicity?
jnz short nonmax386_16 ; nope.
shl savedand,1 ; well then, let's try this one!
inc savedand ; (2**n -1)
mov savedincr,4 ; and reset the increment flag
jmp short nonmax386_16

; 32bit on 386:
code386_32:
mov esi,x ; use ESI for X
mov edi,y ; use EDI for Y

; This is the main processing loop. Here, every T-state counts...

kloop: ; for (k = 0; k <= maxit; k++)

mov eax,esi ; compute (x * x)
imul esi ; ...
shrd eax,edx,FUDGEFACTOR ; ( / fudge)
shr edx,FUDGEFACTOR-1 ; (complete 64-bit shift and check
jne short kloopend1 ; bail out if too high
mov ebx,eax ; save this for below

mov eax,edi ; compute (y * y)
imul edi ; ...
shrd eax,edx,FUDGEFACTOR ; ( / fudge)
shr edx,FUDGEFACTOR-1 ; (complete 64-bit shift and check
jne short kloopend1 ; bail out if too high

mov ecx,ebx ; compute (x*x - y*y) / fudge
sub ebx,eax ; for the next iteration

add ecx,eax ; compute (x*x + y*y) / fudge
cmp ecx,lm ; while (lr < lm)
jae short kloopend1 ; ...

mov eax,edi ; compute (y * x)
imul esi ; ...
shrd eax,edx,FUDGEFACTOR-1 ; ( * 2 / fudge)
add eax,linity ; (above) + linity
mov edi,eax ; save this as y

; (from the earlier code) ; compute (x*x - y*y) / fudge
mov esi,ebx ; save this as x

mov ax,oldcolor ; recall the old color
cmp ax,k ; check it against this iter
jge short chkperiod1
nonmax1:
dec k ; while (k < maxit) (dec to 0 is faster)
jnz short kloop ; while (k < maxit) ...
kloopend1:
jmp short kloopend32 ; we done.

chkperiod1:
mov eax,esi
xor eax,savedx
jnz short chksave1
mov eax,edi
xor eax,savedy
jnz short chksave1
mov period,1 ; note that we have found periodicity
mov k,0 ; pretend maxit reached
jmp short kloopend1
chksave1:
mov ax,k
test ax,savedand
jne short nonmax1
mov savedx,esi
mov savedy,edi
dec savedincr ; time to change the periodicity?
jnz short nonmax1 ; nope.
shl savedand,1 ; well then, let's try this one!
inc savedand ; (2**n -1)
mov savedincr,4 ; and reset the increment flag
jmp short nonmax1

kloopend32:

.8086 ; 386-specific code ends here

kloopend:
cmp orbit_ptr,0 ; any orbits to clear?
je noorbit2 ; nope.
call far ptr scrub_orbit ; clear out any old orbits
noorbit2:

mov ax,k ; set old color
sub ax,10 ; minus 10, for safety
mov oldcolor,ax ; and save it as the "old" color
mov ax,maxit ; compute color
sub ax,k ; (first, re-compute "k")
sub kbdcount,ax ; adjust the keyboard count
cmp ax,1 ; convert any "outlier" region
jge short coloradjust1 ; (where abs(x) > 2 or abs(y) > 2)
mov ax,1 ; to look like we ran through
coloradjust1: ; at least one loop.
mov realcolor,ax ; result before adjustments
cmp ax,maxit ; did we max out on iterations?
jne short wedone ; nope.
mov oldcolor,ax ; set "oldcolor" to maximum
cmp inside,0 ; is "inside" >= 0?
jl wedone ; nope. leave it at "maxit"
mov ax,inside ; reset max-out color to default
cmp periodicitycheck,0 ; show periodicity matches?
jge wedone ; nope.
mov al,period ; reset color to periodicity flag
wedone: ;
mov color,ax ; save the color result
UNFRAME ; pop stack frame
ret ; and return with color

calcmandasm endp

; ******************** Function code16bit() *****************************
;
; Performs "short-cut" 16-bit math where we can get away with it.
;

code16bit proc near

mov si,word ptr x+2 ; use SI for X
mov di,word ptr y+2 ; use DI for Y

start16bit:
mov ax,si ; compute (x * x)
imul si ; ...
cmp dx,0 ; say, did we overflow?
jl end16bit ; (oops. We done.)
mov cx,32-FUDGEFACTOR ; ( / fudge)
loop16bit1:
shl ax,1 ; ...
rcl dx,1 ; ...
jo end16bit ; (oops. overflow)
loop loop16bit1 ; ...
mov bx,dx ; save this for a tad

mov ax,di ; compute (y * y)
imul di ; ...
cmp dx,0 ; say, did we overflow?
jl end16bit ; (oops. We done.)
mov cx,32-FUDGEFACTOR ; ( / fudge)
loop16bit2:
shl ax,1 ; ...
rcl dx,1 ; ...
jo end16bit ; (oops. overflow)
loop loop16bit2 ; ...

mov cx,bx ; compute (x*x - y*y) / fudge
sub bx,dx ; for the next iteration

add cx,dx ; compute (x*x + y*y) / fudge
jo end16bit ; bail out if too high
js end16bit ; ...

cmp cx,word ptr lm+2 ; while (xx+yy < lm)
jae end16bit ; ...

mov ax,di ; compute (y * x)
imul si ; ...
mov cx,33-FUDGEFACTOR ; ( * 2 / fudge)
loop16bit3:
shl ax,1 ; ...
rcl dx,1 ; ...
loop loop16bit3 ; ...
add dx,word ptr linity+2 ; (2*y*x) / fudge + linity
mov di,dx ; save as y

add bx,word ptr linitx+2 ; (from above) (x*x - y*y)/fudge + linitx
mov si,bx ; save as x

mov ax,oldcolor ; recall the old color
cmp ax,k ; check it against this iter
jl short nonmax3 ; nope. bypass periodicity check.
mov word ptr x+2,si ; save x for periodicity check
mov word ptr y+2,di ; save y for periodicity check
call checkperiod ; check for periodicity
nonmax3:

dec k ; while (k < maxit)
jz end16bit ; we done.

jmp start16bit ; try, try again.

end16bit: ; we done.
ret
code16bit endp

; The following routine checks for periodic loops (a known
; method of decay inside "Mandelbrot Lake", and an easy way to
; bail out of "lake" points quickly). For speed, only the
; high-order sixteen bits of X and Y are checked for periodicity.
; For accuracy, this routine is only fired up if the previous pixel
; was in the lake (which means that the FIRST "wet" pixel was
; detected by the dull-normal maximum iteration process).

checkperiod proc near ; periodicity check
mov ax,k ; set up to test for save-time
test ax,savedand ; save on 0, check on anything else
jz checksave ; time to save a new "old" value
mov dx,word ptr x+2 ; load up x
and dx,word ptr savedmask+2 ; truncate to appropriate precision
cmp dx,word ptr savedx+2 ; does X match?
jne checkdone ; nope. forget it.
mov ax,word ptr x ; load up x
and ax,word ptr savedmask ; truncate to appropriate precision
cmp ax,word ptr savedx ; does X match?
jne checkdone ; nope. forget it.
mov dx,word ptr y+2 ; now test y
and dx,word ptr savedmask+2 ; truncate to appropriate precision
cmp dx,word ptr savedy+2 ; does Y match?
jne checkdone ; nope. forget it.
mov ax,word ptr y ; load up y
and ax,word ptr savedmask ; truncate to appropriate precision
cmp ax,word ptr savedy ; does Y match?
jne checkdone ; nope. forget it.
mov period,1 ; note that we have found periodicity
mov k,1 ; pretend maxit reached
checksave:
mov dx,word ptr x+2 ; load up x
and dx,word ptr savedmask+2 ; truncate to appropriate precision
mov word ptr savedx+2,dx ; and save it
mov ax,word ptr x ; load up x
and ax,word ptr savedmask ; truncate to appropriate precision
mov word ptr savedx,ax ; and save it
mov dx,word ptr y+2 ; load up y
and dx,word ptr savedmask+2 ; truncate to appropriate precision
mov word ptr savedy+2,dx ; and save it
mov ax,word ptr y ; load up y
and ax,word ptr savedmask ; truncate to appropriate precision
mov word ptr savedy,ax ; and save it
dec savedincr ; time to change the periodicity?
jnz checkdone ; nope.
shl savedand,1 ; well then, let's try this one!
inc savedand ; (2**n -1)
mov savedincr,4 ; and reset the increment flag
checkdone:
ret ; we done.
checkperiod endp

; ******************** Function code32bit() *****************************
;
; Perform the 32-bit logic required using 16-bit logic
;
; New twice as fast logic,
; Courtesy of Bill Townsend and Mike Gelvin (CIS:73337,520)

local donejp,skip1y,skip2y,squrey,allzero
sub bh,bh
sub cx,cx
mov bp,cx
or ax,ax ;GET LOW HWORD
jz skip1y ;LOW HWORD IS ZERO, ONLY DO HIGH HWORD
mov si,ax
mul ax ;SQUARE LOW HWORD - B*B
mov bh,dh
or di,di ;TEST HIGH HWORD
jz squrey ;HIGH HWORD ZERO, SKIP THE FOLLOWING
mov ax,di
mul si ;GET MIDDLE PART - A*B
adc bp,0 ; SI,CX,BH = 2(A*B)+(B*B)
jmp short skip2y
skip1y: or di,di ;M1=SKIP1Y
jz allzero
skip2y: mov ax,di ;M2=SKIP2Y
mul ax ;SQUARE HIGH HWORD - A*A
squrey: shl bh,1 ;M3=SQUREY
rcl cx,1
rcl bp,1
; jo donejp ; squaring a +ve, top bit known off
shl bh,1
rcl cx,1
rcl bp,1
; jo donejp ; squaring a +ve, 2nd bit known off
shl bh,1
rcl cx,1
rcl bp,1
jo donejp
js donejp ; if went neg have overflow also
allzero:

endm ;#EM

code32bit proc near
;
; BL IS USED FOR THE FLAGS,TWO LOW ORDER BITS ARE "NEGSWT", THIRD BIT IS XSIGN
; XSIGN IS ONE IF THE SIGN OF THE NEW "X" IS NEGATIVE
; NEGSWT IS ONE IF EITHER "X" OR "Y" ARE NEGATIVE, BUT NOT BOTH NEGATIVE
;
xsign equ 00000100b
negswt equ 00000001b

push bp
sub si,si ; make a zero __________
mov bx,si ; BOTH XSIGN & NEGSWT START OFF ZERO
mov di,1 ; MAKE A ONE
mov cx,word ptr y ; cx=y
mov bp,word ptr y+2 ; bp=y+2
cmp bp,si ; y>0?
jns qnotng ; yup
not cx ; nope, negate it
not bp ; ...
inc bl ; INCREMENT negswt
qnotng: mov ax,word ptr x
mov dx,word ptr x+2
cmp dx,si ; x>0?
jns pnotng ; yup
not ax ; nope, negate it
not dx ; ...
inc bl ; INCREMENT negswt
pnotng: mov word ptr absx,ax ; save unsigned x
mov word ptr absx+2,dx ; ...

; iteration loop
nextit: push bp ; save y on stack
push cx ; ...
mov ax,cx ; load y for squaring
mov di,bp ; ...
square done2 ; square di,ax & br to jmp_done2 if overflow
push cx ; return results in bp,cx
push bp ; save y*y on stack
mov ax,word ptr absx ; load x for squaring
mov di,word ptr absx+2 ; ...
square done ; square di,ax & br to done if overflow
mov di,bp ; return results in bp,cx
mov si,cx ; save x*x in di,si
pop dx ; unstack y*y into dx,ax
pop ax ; ...
ADD cx,ax ; calc y*y + x*x
jo done2 ; overflow?
js done2 ; overflow?
cmp bp,word ptr lm+2 ; while (lr < lm)
jb short nextxy ; keep going
jmp short done2 ; magnitude is past limit, bailout
xydone: pop bp ; restore saved bp
ret

;---------------------------------------------------------------------------
;y=nz, x=nz, x+2=z
x2is0: pop ax ; get old y+2
or ax,ax ; test y+2
jz jgotxy
mul si ; do y+2(ax)*x(si)
jgotxy: jmp gotxy

;x=z
xis0: or di,di ; test x+2
jz popy_2 ; zero all done, around again please
mul di ; do y(ax)*x+2(di)
pop ax ; get old y+2
or ax,ax
jz gotxy
mulxyj: jmp mulxy2

;x=z, x+2=z
popy_2: pop ax ; discard old y+2
sub cx,cx ; x==0, so x*y is zero
mov bp,cx ; ...
jmp signok ; go add b and store new y

nextxy: sub si,ax ; subtract y*y from x*x
sbb di,dx ; ...
adc di,word ptr linitx+2 ; ...
mov word ptr x,si ; store new x = x*x+y*y+a
mov word ptr x+2,di ; ...
jns swtxxx ; NO SIGN, NOT NEG
or bl,xsign ; REMEMBER THE NEW "X" IS NEGATIVE
not si ; make it positive in register
not di ; ...
swtxxx: xchg di,word ptr absx+2 ; save the new x, load the old
xchg si,word ptr absx ; ...

; now calculate x*y
sub bh,bh ; zero some registers
sub cx,cx ; ...
mov bp,cx ; ...
pop ax ; get old "y"
or ax,ax ; test "y"
jz yis0 ; br if "y" is zero
or si,si ; test old "x"
jz xis0 ; br if "x" is zero
mov bp,ax ; save old "y"
mul si ; do y(ax)*x(si)
mov ax,bp ; get old "y" again
mov bp,cx ; RE-ZERO BP
mov bh,dh ; save/set low hword(bx)
or di,di ; test old "x+2"
jz x2is0
mul di ; do y(ax)*x+2(di)

yis0: pop ax ; get old "y+2"
or ax,ax ; test y+2
jz gotxy ; br if y+2 is zero
mov dx,si ; dx="x"
mov si,ax ; si=save "y+2"
mul dx ; do y+2(ax)*x(dx)--(si)

mov ax,si ; get old "y+2"
mulxy2: mul di ; do y+2(ax)*x+2(di)

gotxy: shl bh,1
rcl cx,1 ; bp,cx,bx
rcl bp,1
jo jmpxydone
shl bh,1
rcl cx,1
rcl bp,1
jo jmpxydone
shl bh,1
rcl cx,1
rcl bp,1
jo jmpxydone
js jmpxydone ; if went neg have overflow also

test bl,negswt ; ZERO IF NONE OR BOTH X , Y NEG
jz signok ; ONE IF ONLY ONE OF X OR Y IS NEG
not cx ; negate result
not bp ; ...
signok:
shr bl,1
shr bl,1 ;MOVE "XSIGN"(X=NEG) DOWN TO "NEGSWT"

adc bp,word ptr linity+2 ; BP,CX = 2(X*Y)+B
mov word ptr y,cx ; save the new value of y
mov word ptr y+2,bp ; ...
jns jmpnit ; NO SIGN, NOT NEG
inc bl ; INCREMENT NEGSWT
not cx ; negate
not bp ; ...

jmpnit: mov ax,oldcolor ; recall the old color
cmp ax,k ; check it against this iter
jl short chkmaxit ; nope. bypass periodicity check.
call checkperiod ; check for periodicity

chkmaxit:
dec k ; while (k < maxit)
jz jmpxydone ; we done.
cmp show_orbit,0 ; orbiting on?
jne horbit ; yep.
jmp nextit ;go around again

jmpxydone:
jmp xydone ; DOES [(X*X)-(Y*Y)+P] BEFORE THE DEC.

horbit: push bx ; save my flags
push bp ; and registers
push cx ; ...
mov ax,-1 ; color for plot orbit
push ax ; ...
push word ptr y+2 ; co-ordinates for plot orbit
push word ptr y ; ...
push word ptr x+2 ; ...
push word ptr x ; ...
call far ptr iplot_orbit ; display the orbit
add sp,5*2 ; clear out the parameters
pop cx ; restore registers
pop bp ; ...
pop bx ; and flags
jmp nextit ; go around again

code32bit endp

calcmand_TEXT ends

end

