Faster approach to checking for an all-zero buffer in C?

Question

I am searching for a faster method of accomplishing this:

int is_empty(char * buf, int size) 
{
    int i;
    for(i = 0; i < size; i++) {
        if(buf[         


        

Answer 1

Inline assembly version of the initial C code (no error checking, if uiSize is == 0 and/or the array is not allocated exceptions will be generated. Perhaps use try {} catch() as this might be faster than adding a lot of check to the code. Or do as I do, try not to call functions with invalid values (usually does not work). At least add a NULL pointer check and a size != 0 check, that is very easy.

 unsigned int IsEmpty(char* pchBuffer, unsigned int uiSize)
 {
    asm {
      push esi
      push ecx         

      mov esi, [pchBuffer]
      mov ecx, [uiSize]

      // add NULL ptr and size check here

      mov eax, 0

    next_char:
      repe scasb           // repeat string instruction as long as BYTE ptr ds:[ESI] == 0
                           // scasb does pointer arithmetic for BYTES (chars), ie it copies a byte to al and increments ESI by 1
      cmp cx,0             // did the loop complete?
      je all_chars_zero    // yes, array is all 0
      jmp char_not_zero    // no, loop was interrupted due to BYTE PTR ds:[ESI] != 0

    all_chars_zero:        
      mov eax, 1           // Set return value (works in MASM)
      jmp end  

    char_not_zero:
      mov eax, 0          // Still not sure if this works in inline asm

    end:
      pop ecx
      pop esi          
  }
}

That is written on the fly, but it looks correct enough, corrections are welcome. ANd if someone known about how to set the return value from inline asm, please do tell.