How to
calculate the sine assembly language ?
Phantom Lord (C) 1997
Music by SHOV
Probably many have noticed that almost all the effects are
composed of objects changing or moving along a trajectory on
the sine. Many of course can argue that there are effects that
change their shape or coordinates does not sine. To which I can
only reply: "You not right, young man! ". As said
a very good scholar:
Any functional relationship
can be expressed in terms of functions
sine and cosine.
But we - mathematics and we know that
sin (x) = cos (x-pi / 2), so the phrase can be
transform as follows:
Any functional relationship
can be expressed in terms of
sinus.
(C) Phantom Lord
We return to the topic. So we need to have
sine. We define it with the level of BASIC.
10 let adr = 49152
20 for n = 0 to 2 * pi step pi/128
30 poke adr, sin (n) * 127
40 let adr = adr +1
50 next n
As a result, we obtain a table of 256
bytes. Each value is the table
One of the values of sin (n) * 127. We
multiplied sin (n) at 127, to increase
its range to [-1,1] to
[-127.127]. Now if we take the values of
table strictly in order, we will
take successive values of
sin (n) * 127.
Write a program for modifying the sine
color attributes of the screen.
AGAIN EI
HALT
CALL INC_SIN
CALL SIN
CALL IZM
LD A, # 7F
IN A, (# FE)
AND 1
JR NZ, AGAIN
RET
INC_SIN LD A, 0
INC A
LD (INC_SIN +1), A
RET
SIN LD A, (INC_SIN +1)
LD L, A
LD H, # C0
LD A, (HL)
RET
IZM LD HL, # 5800
LD DE, # 5801
LD BC, 767
LD (HL), A
LDIR
RET
INC_SIN procedure allows us to run the entire table, since
all the values of 256, while increasing 255 per unit once we
get 0, ie element belonging to the set of definitions of our
function. This condition is called the frequency of the sine
function.
SIN procedure selects from a table sinus
following value, and IZM fills the screen attributes selected
value.
The transition from "pure" sine to
some advanced features.
ABS (SIN (X)) - module sinus.
Of course in mathematics of high school you
probably know that the sine function module is periodic with
period PI. Let's consider segment of the restriction of SIN (X)
on poluotrezke [0, PI / 2). It is easy to notice in this case
the functions are identical. Write a program calculated the
function ABS (SIN X) based on the reasoning set forth above:
A_1 CALL SIN_INC
CALL SIN
JR A_1
SIN_INC LD A, 0
INC A
AND 127
LD (SIN_INC +1), A
RET
SIN ...
As you can see after the team we have put INC A AND 127,
thereby limiting the value of SIN only for positive numbers, ie
on ABS (SIN (X)).
-ABS (SIN (X))
Obviously, if prodelyvat similar arguments, we obtain a program
similar to the previous one and differs from
it only routine SIN_INC:
SIN_INC LD A, 0
INC A
AND 127
ADD A, 128
LD (SIN_INC +1), A
RET
Now the question may arise:
And it gives our program?
This will give your program the realism. Tell me, what nicer
looking, by bouncing to the laws of physics ball
or mayachuschuyu up-down physical
form?
You decide.
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