On Mon, Dec 29, 2014 at 10:34 PM, Max Filippov <jcmvbkbc@xxxxxxxxx> wrote: > On Tue, Dec 30, 2014 at 3:25 AM, Vinícius Tinti <viniciustinti@xxxxxxxxx> wrote: >> I was looking the kernel source code and there are a lot of places in >> which either "(expression) ? 1 : 0" or "(expression) ? 0 : 1" appear. >> As fair as I can tell both can be replaced by "!!expression" and >> "!expression". >> >> Moreover there it seems that using "!!" does not add a "nopl" >> instruction at the end of the call. Does anybody knows why? > > It seems that the nop instruction is inserted for alignment, and if you > reverse the order of functions in your c source, nop will still be > inserted between them. I notice that too. If you use both functions in other code they both will have the nopl. And "!expression" is as good as the "(expression) ? 0 : 1". Thus no gain and worse readability I think. >> 0000000000000000 <mod_if>: >> 0: 31 c0 xor %eax,%eax >> 2: 85 ff test %edi,%edi >> 4: 0f 95 c0 setne %al >> 7: c3 retq >> 8: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1) >> f: 00 >> >> 0000000000000010 <mod_x>: >> 10: 31 c0 xor %eax,%eax >> 12: 85 ff test %edi,%edi >> 14: 0f 95 c0 setne %al >> 17: c3 retq > > -- > Thanks. > -- Max -- Simplicity is the ultimate sophistication _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
