In article <1993Mar5.105326.22133@metapro.DIALix.oz.au> bernie@metapro.DIALix.oz.au (Bernd Felsche) writes: >In <39610@cbmvax.cbm.commodore.com> > >If at all possible, don't use trig functions at all. > >Most graphics applications are accurate enough with the first 2 >or 3 terms of an equivalent Taylor series. Error is usually of >the order of 1:1000. > The following code is what I use. It's accurate enough for computing texture map coordinates in my ray-tracer: acos:: ; input d0=cos output d0=acos(d0) 1 -> 0 0 > .25 -1 > .5 ; trashes d1/d2,a0 tst.w d0 bmi.s negacos posacos: move d0,d2 and.w #$001f,d2 lsr #5,d0 add d0,d0 lea acos_tbl(pc),a0 move 2(a0,d0.w),d1 move 0(a0,d0.w),d0 sub d0,d1 muls d2,d1 asr.w #5,d1 add d1,d0 rts negacos: neg.w d0 bsr.s posacos neg.w d0 add.w #$7ffe,d0 ; acos(-x) = .5-acos(x) rts and here's the boring part: acos_tbl: dc.w $3fff dc.w $3ff5 dc.w $3feb dc.w $3fe1 dc.w $3fd7 dc.w $3fcd dc.w $3fc2 dc.w $3fb8 dc.w $3fae dc.w $3fa4 dc.w $3f9a dc.w $3f8f dc.w $3f85 dc.w $3f7b dc.w $3f71 dc.w $3f67 dc.w $3f5d dc.w $3f52 dc.w $3f48 dc.w $3f3e dc.w $3f34 dc.w $3f2a dc.w $3f1f dc.w $3f15 dc.w $3f0b dc.w $3f01 dc.w $3ef7 dc.w $3eec dc.w $3ee2 dc.w $3ed8 dc.w $3ece dc.w $3ec4 dc.w $3eb9 dc.w $3eaf dc.w $3ea5 dc.w $3e9b dc.w $3e91 dc.w $3e87 dc.w $3e7c dc.w $3e72 dc.w $3e68 dc.w $3e5e dc.w $3e54 dc.w $3e49 dc.w $3e3f dc.w $3e35 dc.w $3e2b dc.w $3e21 dc.w $3e16 dc.w $3e0c dc.w $3e02 dc.w $3df8 dc.w $3dee dc.w $3de3 dc.w $3dd9 dc.w $3dcf dc.w $3dc5 dc.w $3dbb dc.w $3db0 dc.w $3da6 dc.w $3d9c dc.w $3d92 dc.w $3d88 dc.w $3d7d dc.w $3d73 dc.w $3d69 dc.w $3d5f dc.w $3d55 dc.w $3d4a dc.w $3d40 dc.w $3d36 dc.w $3d2c dc.w $3d22 dc.w $3d17 dc.w $3d0d dc.w $3d03 dc.w $3cf9 dc.w $3cee dc.w $3ce4 dc.w $3cda dc.w $3cd0 dc.w $3cc6 dc.w $3cbb dc.w $3cb1 dc.w $3ca7 dc.w $3c9d dc.w $3c92 dc.w $3c88 dc.w $3c7e dc.w $3c74 dc.w $3c6a dc.w $3c5f dc.w $3c55 dc.w $3c4b dc.w $3c41 dc.w $3c36 dc.w $3c2c dc.w $3c22 dc.w $3c18 dc.w $3c0e dc.w $3c03 dc.w $3bf9 dc.w $3bef dc.w $3be5 dc.w $3bda dc.w $3bd0 dc.w $3bc6 dc.w $3bbc dc.w $3bb1 dc.w $3ba7 dc.w $3b9d dc.w $3b93 dc.w $3b88 dc.w $3b7e dc.w $3b74 dc.w $3b6a dc.w $3b5f dc.w $3b55 dc.w $3b4b dc.w $3b41 dc.w $3b36 dc.w $3b2c dc.w $3b22 dc.w $3b18 dc.w $3b0d dc.w $3b03 dc.w $3af9 dc.w $3aef dc.w $3ae4 dc.w $3ada dc.w $3ad0 dc.w $3ac5 dc.w $3abb dc.w $3ab1 dc.w $3aa7 dc.w $3a9c dc.w $3a92 dc.w $3a88 dc.w $3a7e dc.w 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$0eb5 dc.w $0e98 dc.w $0e7b dc.w $0e5d dc.w $0e40 dc.w $0e22 dc.w $0e04 dc.w $0de5 dc.w $0dc7 dc.w $0da8 dc.w $0d89 dc.w $0d6a dc.w $0d4a dc.w $0d2a dc.w $0d0a dc.w $0ce9 dc.w $0cc8 dc.w $0ca7 dc.w $0c86 dc.w $0c64 dc.w $0c42 dc.w $0c1f dc.w $0bfc dc.w $0bd9 dc.w $0bb5 dc.w $0b91 dc.w $0b6c dc.w $0b47 dc.w $0b22 dc.w $0afc dc.w $0ad5 dc.w $0aae dc.w $0a87 dc.w $0a5f dc.w $0a36 dc.w $0a0d dc.w $09e2 dc.w $09b8 dc.w $098c dc.w $0960 dc.w $0933 dc.w $0905 dc.w $08d6 dc.w $08a6 dc.w $0875 dc.w $0844 dc.w $0810 dc.w $07dc dc.w $07a6 dc.w $076f dc.w $0736 dc.w $06fb dc.w $06be dc.w $067f dc.w $063e dc.w $05fa dc.w $05b2 dc.w $0567 dc.w $0518 dc.w $04c4 dc.w $0469 dc.w $0407 dc.w $039a dc.w $031e dc.w $028c dc.w $01cc dc.w $0000 -- *-------------------------------------------*---------------------------* |Chris Green - Graphics Software Engineer - chrisg@commodore.COM f | Commodore-Amiga - uunet!cbmvax!chrisg n |My opinions are my own, and do not - icantforgettheimpression o �