CODEWITHSUNDEEP
cassembly
ThePom
ThePom

Reputation: 95

x64 inline assembly in C

I am trying to code the sum of natural numbers using inline x64 assembly in C but it isn't working.

#include <stdio.h>

int unsigned(n)
{
    __asm__
    {
            mov     ecx, n;
            mov     eax, 0;
            cmp     ecx, 0;
            je ende;
    label:
            add eax, ecx;
            loop label;

    ende:

    }
}

I get the following error: 

summer.c:4:1: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘{’ token

And also how can I define the n variable? Is it better to do it in the inline assembly or in the C code?

Upvotes: 1

Views: 518

Answers (1)

Matteo Italia
Matteo Italia

Reputation: 126777

The compiler is complaining because your function declaration doesn't make sense. unsigned is a reserved keyword, call your function in some other way; also, you have to specify the type of the parameter. 

int f(int n) 
{
   ...

As for the assembly, the syntax depends from the toolchain you are using, depending from it you may have to use the hideous AT & T. syntax (or to specify some magic command to switch to Intel syntax and back).

(by the way, xor eax, eax is more idiomatic than mov eax, 0)

Upvotes: 1

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