Sinus function
ZXNet echo conference «code.zx»
Greetings, Igor!
Mon 3 Jul 2000 at 03:08:14 Igor Kiselev and All were talking
on the topic Sinus function.
IK> Tell me about the subject, it would be nice to have the source
IK> method of calculating the sine function.
If you are interested in methods for generating sine tables for all sorts of effects, then
I can recommend my procedure.
A little theory:
This procedure does not calculate the sine table, it only unpacks it from
17 byte data table.
The table stores the second derivatives of the sine function for angles from 0 to 64
degrees (the period of the function is not 360, but 256 degrees for convenience).
At the entrance
;D is the most significant byte of the address of the beginning of the 512-byte signed sine table.
The output is a function table (HL)+(256+HL)=255sin(L)
INISIN LD HL,SINTAB-1
LD E,255
LD BC,#06FA
INS INC E
LD A,E
AND 3
JR NZ,$+3
INC HL
XOR A
RLC(HL)
R.L.A.
RLC(HL)
R.L.A.
DEC A
ADD A,B
LD B,A
ADD A,C
LD C,A
CALL INSSR
PUSH DE
LD A,128
SUB E
LD E,A
LD A,C
CALL INSSR
POP DE
BIT 6,E
JR Z,INS
RET
INSSR LD (DE),A
SET 7,E
N.E.G.
LD(DE),A
INC D
SBC A,A
LD(DE),A
RES 7,E
XOR A
LD(DE),ADEC D
RET
SINTAB ;packed data
DB #58,#56,#15,#55
DB #49,#21,#85,#52
DB #21,#54,#88,#54
DB #85,#52,#15,#48,#55
Example:
sinus equ #c000
ld d,sinus/256
call inisin
You can get the sine value (from -255 to +255) like this:
;in L-angle value
ld h,sinus/256
ld e,(hl)
inc h
ld d,(hl)
Congratulations, Igor!
Vivid/Brainwave^X-Project was with you.