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C code with assembly

In C programming, assembly code can be embedded within the C code using the inline assembly feature. Inline assembly is a way to embed assembly code within C code, and it allows C code to access and manipulate hardware directly, bypassing the normal C language restrictions. Inline assembly is achieved using the asm.

Code Example

#include <stdio.h>

int main() {
   int num1 = 4;
   int num2 = 3;
   int sum;
   
   asm ("movl %1, %%eax; addl %2, %%eax; movl %%eax, %0;"
        : "=r" (sum)
        : "r" (num1), "r" (num2)
        : "%eax");
   
   printf("The sum is: %d\n", sum); // 7
   return 0;
}

In this example, the assembly code is enclosed in curly braces and preceded by the asm keyword. The code performs the same addition operation as before, but it uses valid x86 assembly code that loads the values of num1 and num2 into registers and performs the addition using the addl instruction. The result is then stored back into the sum variable using the movl instruction.

Note that the assembly code is using the % character to represent registers and operands, and that the operands are separated by commas. The C code is also using inline assembly with constraints, which specify how the input and output values of the assembly code should be handled. In this case, the r constraint is used to indicate that the input and output values are general-purpose registers, and the %eax constraint is used to specify that the eax register is being used. The = and : characters are used to separate the output and input operands, respectively.





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