[Python-Dev] check for PyUnicode_READY look backwards

[Scott Dial]

On 10/7/2011 7:13 PM, Terry Reedy wrote:
> On 10/7/2011 10:06 AM, Nick Coghlan wrote:
>> FWIW, I don't mind whether it's "<  0" or "== -1", so long as there's a
>> comparison there to kick my brain out of Python boolean logic mode.
> 
> Is there any speed difference (on common x86/64 processors and
> compilers)?  I would expect that '< 0' should be optimized to just check
> the sign bit and 'if n < 0' to 'load n; jump-non-negative'.
> 

There are several different ways to express those operators depending on
the context. If "n" is worth moving into a register, then "<0" will get
to use a "test" and it's fewer instruction bytes than a "cmp", but
otherwise, it is no better. So, there is a very special case where "<0"
is better, but I think you'd be hard-pressed to measure it against the
noise.

-- 
Scott Dial
scott at scottdial.com