30 lines
1.1 KiB
ArmAsm
30 lines
1.1 KiB
ArmAsm
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;=========================================================================
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;Trig functions for GFX routines Copyright (c) 1995 by Mark I Manning IV
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;=========================================================================
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CosTab equ SinTab+0800 ;A Right angle foreward in table!
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;-------------------------------------------------------------------------
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;Return Sin and Cos of angle AX in variables of same name
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SinCos:
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and ax,0fff ;4096 degrees = 0 degrees
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mov bx,ax ;Put into an indexing reg
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add bx,bx
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mov ax,SinTab[bx] ;Get Sin(N)
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mov Sin,ax ;Bah no MOV Sin,[BX]... Crap processor!
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;Note.
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; Can NOT use mov ax,SinTab[2*ebx] because in following code BX may go
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; negative and 2* a negative number = DOUBLY NEGATIVE!
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cmp bx,01800 ;Was Sin(N) in last quadrant of circle?
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if nl sub bx,02000 ;Cos(N) must be in first quadrant then
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mov bx,CosTab[bx] ;Get Cos(n)
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mov Cos,bx ;Exits with Sin in AX and Cos in BX too!
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ret
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;=========================================================================
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