gistfile1.txt

  uint64_t divide(uint64_t x) const {
      /* instructions ending with a q are 64 bits instructions 
        add is 32 bits, addq is 64 bits 

        see http://www.cs.cmu.edu/~fp/courses/15213-s07/misc/asm64-handout.pdf

        see http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html

   __asm__("movq %0, %%rax"
          : "=r" (x)

"=r" output
"r" input
"0" here specifies the same constraint as the 0th output variable.

       */
    //
    __asm__(

    // instructions

            "movq %0, %%rax\n\t"  // Store 0 in register rax   %% binds rax to variable x
            "mulq %1\n\t"         // Multiply by 1 what is in the register rax (useless?)
            "subq %%rdx, %0\n\t"  // Substract 0 from register rdx %% binds m do rdx so initially rdx contains variable m
            "shrq %0\n\t"         // logical right shift <shrq k,D> =  < D <- D >> k>, but k=0 (useless?)
            "addq %%rdx, %0\n\t"  // the %% binds p to register rdx and adds 0 to it
            "shrq %%cl, %0\n\t"   // logical right shift  (cl is a 8-bit register) x is binded to register cl

    // list of clobbered registers
            : "=r" (x)
            : "r" (m), "c" (p), "0" (x)
            : "rax", "rdx");
    return x;
  }