Author: Dann Corbit
Date: 19:06:49 11/17/05
Go up one level in this thread
On November 17, 2005 at 21:20:01, Daniel Mehrmannn wrote:
>On November 17, 2005 at 21:08:06, Dann Corbit wrote:
>
>>On November 17, 2005 at 18:34:34, Daniel Mehrmannn wrote:
>>
>>>On November 17, 2005 at 18:13:36, Dann Corbit wrote:
>>>
>>>>On November 17, 2005 at 17:05:24, Jarkko Pesonen wrote:
>>>>
>>>>>http://www.uciengines.de/UCI-Engines/TogaII/togaii.html
>>>>>
>>>>>engine name Toga 1.0MV.6
>>>>>
>>>>
>>>>static int full_search(board_t * board, int alpha, int beta, int depth, int
>>>>height, mv_t pv[], int node_type) {
>>>>// ...
>>>>// I set FutilityMargin in the general case, because some paths
>>>>// could leave it uninitialized.
>>>> int FutilityMargin = FutilityMargin3;
>>>>
>>>>Consider the following when depth >= 3:
>>>>
>>>> if (depth < 2)
>>>> FutilityMargin = FutilityMargin1;
>>>> else if (depth < 3)
>>>> FutilityMargin = FutilityMargin2;
>>>> /* else
>>>> FutilityMargin = FutilityMargin3; */
>>>>
>>>>Perhaps futility pruning is never used in such a case, but then if so there is
>>>>no harm in setting the value.
>>>
>>>btw this looks like a very slow coding. It's better to use here switch()/case
>>>stuff for an faster code instead the expensive if() stuff.
>>
>>A switch also branches. The odds of a mispredicted branch are the same.
>>
>>If a switch were a trillion times faster than an if(), then a change to switch
>>in this instance would not speed up Toga by even one tenth of one percent. I am
>>absolutely sure of it, without having measured.
>
>I disagree. Okay, basicly it depends what are you doing and how often it called.
>In my experience a switch call is faster than if().
In this case, it makes no difference.
If you code with switch() because you think it is faster than if() then you are
making a terrible mistake[*]. Code with the construct that is the most clear
every time.
[*] If you have profiled and some patch of code is causing a problem because of
slowness and if you see that it is using an if and if it profiles faster with a
switch, then change to a switch and explain why you did it in a comment.
Else, use if() when it is more natural.
P.S.
I have profiled chains of if() and switch() statements and arrays of function
pointers and many other approaches to conditional changes. Which method is
faster will change from compiler to compiler and even from compiler version to
compiler version with the same compiler.
A bit of searching the archives will even show some benchmarks I have provided
to this forum in that area [IIRC].
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