Assembler

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May 6th, 2003, 04:39 PM
kakalake

Assembler

Hello!
Can someone help me with the following assemblercode

Code:

extern "C" long double _cdecl exp (double x) _exp PROC NEAR PUBLIC _exp FLDL2E FLD QWORD PTR [ESP+4] //; x FMUL //; z = x*log2(e) FIST DWORD PTR [ESP+4] // round(z) SUB ESP, 12 MOV DWORD PTR [ESP], 0 MOV DWORD PTR [ESP+4], 80000000H FISUB DWORD PTR [ESP+16] //; z - round(z) MOV EAX, [ESP+16] ADD EAX,3FFFH MOV [ESP+8],EAX JLE SHORT UNDERFLOW CMP EAX,8000H JGE SHORT OVERFLOW F2XM1 FLD1 FADD //; 2^(z-round(z)) FLD TBYTE PTR [ESP] //; 2^(round(z)) ADD ESP,12 FMUL //; 2^z = e^x RET UNDERFLOW: FSTP ST FLDZ //; return 0 ADD ESP,12 RET OVERFLOW: PUSH 07F800000H //; +infinity FSTP ST FLD DWORD PTR [ESP] //; return infinity ADD ESP,16 RET _exp ENDP return 0 }

I want to use this function in my c++ programm. I am using Vc++ 6.0.

Thanks in advance
May 6th, 2003, 05:09 PM
Paul McKenzie

It's not C++, so how do you propose to use it in a C++ program?

Do you mean

a) translate it into C++ code or

b) place it in-line into the C++ code or

c) use a seperate assembler and compile the code. Then include the obj in your project

Which one a), b), or c), or do you have something else in mind?

Regards,

Paul McKenzie
May 6th, 2003, 05:16 PM
kakalake

I want to use it inline in my code:

If you are interested you can show me shortly how to solve my problem with each of your suggested solutions.

Thanks
May 6th, 2003, 05:27 PM
Paul McKenzie

Quote:

Originally posted by kakalake
I want to use it inline in my code:

If you are interested you can show me shortly how to solve my problem with each of your suggested solutions.

Thanks

You have to use the _asm keyword. It should be documented in the VC++ help.

To translate it to C++, you have to know what the code is supposed to do and just rewrite it in C++.

To compile it using a separate assembler, you have to get MASM or some other assembler to create an obj. Then you include the obj file in your project.

Regards,

Paul McKenzie
May 6th, 2003, 05:41 PM
kakalake

I already used the keyword _asm but it still doesn´t work.

Code:

double exp (double x) { _asm { FLDL2E FLD QWORD PTR [ESP+4] //; x FMUL //; z = x*log2(e) FIST DWORD PTR [ESP+4] // round(z) SUB ESP, 12 MOV DWORD PTR [ESP], 0 MOV DWORD PTR [ESP+4], 80000000H FISUB DWORD PTR [ESP+16] //; z - round(z) MOV EAX, [ESP+16] ADD EAX,3FFFH MOV [ESP+8],EAX JLE SHORT UNDERFLOW CMP EAX,8000H JGE SHORT OVERFLOW F2XM1 FLD1 FADD //; 2^(z-round(z)) FLD TBYTE PTR [ESP] //; 2^(round(z)) ADD ESP,12 FMUL //; 2^z = e^x RET UNDERFLOW: FSTP ST FLDZ //; return 0 ADD ESP,12 RET OVERFLOW: PUSH 07F800000H //; +infinity FSTP ST FLD DWORD PTR [ESP] //; return infinity ADD ESP,16 RET } return 0; }

Everything works fine but when the function jumps to the label Underflow, or Overflow it breaks with an access violation error. This error occurs when the label tries to RETurn with RET to the position where it was called.
May 6th, 2003, 06:24 PM
rxbagain

You must not call RET in your directly in your code. This will invalidate the stack frame becuase when you entered the procedure, the compiler added this code to your own

Code:

push ebp mov ebp, esp sub esp, 40h push ... push... ...

By calling RET in your code, you did not cleaned the ESP, so the return address is invalid.

What you have to do is declare a double variable to store the result instead of directly accessing offsets of the esp and in your code, add a JUMPLABEL before the return statement and jump to that label instead of issuing RET.

Code:

double exp (double x) { double retval; __asm { ... ... JMP RETURN_RESULT UNDERFLOW: ... ... JMP RETURN_RESULT OVERFLOW: ... ... JMP RETURN_RESULT } RETURN_RESULT: return retval; }

Hope this will help you.
May 6th, 2003, 06:54 PM
kakalake

i have not written the code. I haven´t any experiences with assembler. Could you show me what you mean?

Thanks
May 6th, 2003, 08:52 PM
rxbagain

This is the modified code. I removed the ESP and replaced them with variable to avoid offset error.

Code:

double exp (double myval) { double retval = 0; DWORD tempval[3]; __asm { FLDL2E FLD QWORD PTR [myval] //; x FMUL //; z = x*log2(e) FIST DWORD PTR [myval] // round(z) MOV DWORD PTR [tempval], 0 MOV DWORD PTR [tempval + 4], 80000000H FISUB DWORD PTR [myval] //; z - round(z) MOV EAX, DWORD PTR [myval] ADD EAX,3FFFH MOV [tempval+8],EAX JLE SHORT UNDERFLOW CMP EAX,8000H JGE SHORT OVERFLOW F2XM1 FLD1 FADD //; 2^(z-round(z)) FLD TBYTE PTR [tempval] //; 2^(round(z)) FMUL //; 2^z = e^x JMP RETURN_RESULT UNDERFLOW: FSTP ST FLDZ //; return 0 JMP RETURN_RESULT OVERFLOW: PUSH 07F800000H //; +infinity FSTP ST ADD ESP, 4 FLD DWORD PTR [tempval] //; return infinity RETURN_RESULT: FST QWORD PTR [retval]; } return retval; }

Hope this will help you.
May 7th, 2003, 04:08 AM
kakalake

Thanks a lot to all especially to rxbagain.

Thanks, thanks, thanks ....