{─ Fido Pascal Conference ────────────────────────────────────────────── PASCAL ─
Msg  : 342 of 352
From : Sean Palmer                         1:104/123.0          13 Apr 93  13:52
To   : David Jirku
Subj : Fast math
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 DJ> I was just wondering how to speed up some math-intensive
 DJ> routines I've got here. For example, I've got a function
 DJ> that returns the distance between two objects:

 DJ> This is way to slow. I know assembly can speed it up, but
 DJ> I know nothing about asm. so theres the problem. Please
 DJ> help me out, any and all source/suggestions welcome!

I can whip up this integer square-root algorithm in assembly to use
386 registers... will be REAL fast! Else I could post the 16-bit version
I guess...

This is tested code. Works on my 386sx fine... Auto-rounds the result. }

function iSqrt(x:longint):word;assembler;asm  {requires a 386, and TP 6.0}
 db $66; xor ax,ax;            {xor eax,eax}
 db $66; xor dx,dx;            {xor edx,edx}
 db $66; mov di,word ptr x;    {mov edi,x}
 mov cx,32;
@L:
 db $66; shl di,1;             {shl edi,1}
 db $66; rcl dx,1;             {rcl edx,1}
 db $66; shl di,1;             {shl edi,1}
 db $66; rcl dx,1;             {rcl edx,1}
 db $66; shl ax,1;             {shl eax,1}
 db $66; mov bx,ax;            {mov ebx,eax}
 db $66; shl bx,1;             {shl ebx,1}
 db $66; inc bx;               {inc ebx}
 db $66; cmp dx,bx;            {cmp edx,ebx}
 jl @S;
 db $66; sub dx,bx;            {sub edx,ebx}
 db $66; inc ax;               {inc eax}
@S: loop @L;
 db $66; add ax,$8000; dw 0;   {add eax,$00008000}  {round result in hi word}
 db $66; shr ax,16;            {shr eax,16}  {to ax}
 end;