Using assembler for C function

[Simon666]

Hello,

I make use of a function SquareRoot that is defined in assembler. I'm not sure whether it works correctly so I asked some people for the code. Below is what I received:

================================================

* 
*   +--------------------------------------------+ 
*   | Unsigned32 SquareRoot(Unsigned32 Argument) | 
*   +--------------------------------------------+ 
* 
*   Functional description : Computes the square root of an Unsigned32. 
* 
*   Algorithm   :  Newton_iteration -> x(n+1) = 1/2 [N/x(n) + x(n)] 
*                  (See EDN 26/11/87 : DESIGN IDEAS, p250). 
* 
 XDEF _SquareRoot 
_SquareRoot 
 START_INPUT_PARAMETERS D2 
 DECLARE_INPUT_PARAMETER 4,SQRT_ARGUMENT 
* 
 CLR.L D2                       reset msw of d2 ! 
* 
*   Compute the "first guess" 
* 
*   1. Find the most significant non_zero bit pair in N. 
*      (A bit pair is bits b,b-1 with b even) 
*   2. Define i=b/2 
*          2^ 
*   3. Create two numbers : 
*          N divided by 2^i  & 2^i 
*   4. Average them to get guess1, the first guess. 
* 
 MOVE.L SQRT_ARGUMENT(SP),D0 
 MOVE.L D0,D1                   save argument 
 BEQ.B SQRT_900                 eq => sqrt(000) = 000 
 BPL.B SQRT_100                 pl => bit pair "32",31 = zero ! 
* 
*   Compute sqrt for N >> 
* 
 CLR.W D0 
 SWAP D0                        do = N/2^16 
* 
*   See if N is 0FFFE0001 or greater; if so return 0FFFFH 
*    (We know that 0FFFFH squared = 0FFFFE0001H) 
* 
 MOVE.W D0,D2 
 NEG.W D2 
 ROXR.W #1,D0 
 SUBQ.W #2,D2 
 BHI.B SQRT_200                 hi => N < 0FFFE0000H 
* 
*   N = FFFExxxx or FFFFxxxx 
* 
 OR.W D1,D2 
 BNE.B SQRT_900 
 SUBQ.W #1,D0 
 BRA.B SQRT_900 
* 
*   The first guess for bit pair 32/31 = zero 
* 
SQRT_100 
 ADD.L D0,D0                    move bits b-1 -> b 
 OR.L D1,D0                     all non_zero bit-pairs in b now 
 MOVE.W #15,D2                  b/2 (30 .. 0) 
* 
*   Find the most_significant bit_pair 
* 
SQRT_110 
 LSL.L #2,D0                    test bit_pair 
 DBCS D2,SQRT_110               until non-zero bit_pair is found ... 
* 
*   Calculate the first_guess 
* 
 MOVE.L D1,D0                   N 
 LSR.L D2,D0                    N/2^i 
 ADD.W #16,D2                   i+16 
 BSET.L D2,D2                   d2hi = 2^i 
 SWAP D2                        d2lo = 2^i 
 ADD.W D2,D0                    extend d0 = N/2^i + 2^i  (17 bits) 
 ROXR.W #1,D0                   the first guess ... 
* 
*   Aplly Newton's Method. 
* 
SQRT_200 
 MOVE.L D1,D2                   N 
 DIVU D0,D2 
 ADD.W D2,D0 
 ROXR.W #1,D0                   d0 = 1/2[N/guess1 + guess1] => guess2 
* 
 MOVE.L D1,D2                   n 
 DIVU D0,D2 
 CMP.W D0,D2                    is N/guess2 < guess2 ? 
 BHS.B SQRT_900                 hs => no, guess2 = sqrt 
 ADD.W D2,D0 
 ROXR.W #1,D0                   guess3 
* 
 MOVE.W D0,D2 
 MULU.W D2,D2                   N**2 
 CMP.L D1,D2                    is this > N ? 
 BLS.B SQRT_900                 ls => sqrt 
 SUBQ.W #1,D0                   guess3-1 = sqrt 
* 
*   Exit _SquareRoot 
* 
SQRT_900 
 AND.L #0FFFFH,D0               long(); 
 RESTORE_REGISTERS D2 
 RTS 

================================================

Anybody knows how to define a function unsigned int SquareRoot(unsigned int) out of this and compile the thing as to test it?

[Andreas Masur]

[ Moved thread ]

[Bob Davis]

Well, from the assembly code you gave, it's obvious that it's not for an x86 architecture, and therefore you aren't running Windows or using VC++. What I'm getting at is that we can't tell you anything about how to do this unless we knew what compiler/assembler you're using.