Qsearch of Stockfish 1.7.1

[Ferdy]

There could be a bug in updating oldAlpha.
At the top of it there is oldAlpha = alpha, at the middle there is a possibility that alpha will be updated with staticValue or bestValue, if it happens then oldAlpha will now be wrong.
At the end saving of tt info. will be affected.

[zamar]

There is no bug.

oldAlpha as the name puts it is "original alpha", this is initialized in the beginning of the qsearch and must not be changed at any point

[QED]

oldAlpha as the name puts it is "original alpha", this is initialized in the beginning of the qsearch and must not be changed at any point :)

Then why there is "Value alpha" as an argument of qsearch(), and not "const Value oldAlpha"?

[zamar]

oldAlpha as the name puts it is "original alpha", this is initialized in the beginning of the qsearch and must not be changed at any point

Then why there is "Value alpha" as an argument of qsearch(), and not "const Value oldAlpha"?

From compiler's point of view this would definitely be better, but I don't know if it is harder to read for a human? I'll discuss about this with Marco.

[QED]

oldAlpha as the name puts it is "original alpha", this is initialized in the beginning of the qsearch and must not be changed at any point :)

Then why there is "Value alpha" as an argument of qsearch(), and not "const Value oldAlpha"?

From compiler's point of view this would definitely be better, but I don't know if it is harder to read for a human? I'll discuss about this with Marco.

Another possibiliy would be "const Value alpha" for the argument, and "Value newAlpha" for the variable.

I am new to serious chess programming, so I am not sure which is more readable.

[mcostalba]

oldAlpha as the name puts it is "original alpha", this is initialized in the beginning of the qsearch and must not be changed at any point

Then why there is "Value alpha" as an argument of qsearch(), and not "const Value oldAlpha"?

From compiler's point of view this would definitely be better, but I don't know if it is harder to read for a human? I'll discuss about this with Marco.

Another possibiliy would be "const Value alpha" for the argument, and "Value newAlpha" for the variable.

I am new to serious chess programming, so I am not sure which is more readable.

In chess programming is a well estabilished convention to call the search functions passing as arguments: 'alpha' and 'beta'

So I would not change that well understood and general convention used almost always in literature when talking about alpha-beta search.

[Ferdy]

There is no bug.

oldAlpha as the name puts it is "original alpha", this is initialized in the beginning of the qsearch and must not be changed at any point

The thing I see under current scheme is that, ss[ply].pv[ply] can not guarantee to contain a move

Code: Select all

 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);

[mcostalba]

There is no bug.

oldAlpha as the name puts it is "original alpha", this is initialized in the beginning of the qsearch and must not be changed at any point

The thing I see under current scheme is that, ss[ply].pv[ply] can not guarantee to contain a move

Code: Select all

 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, d, ss[ply].pv[ply]);

So ?

[Teemu Pudas]

It's supposed to contain a move if and only if at least one of the moves is better than standing pat.

[zamar]

When we initialize a node we set (see SearchStack::init()):

pv[ply] = pv[ply + 1] = MOVE_NONE;

So if there is a move better than stand pat score it'll be saved in TT. If not we call TT.store(move=MOVE_NONE) which means that old move won't be overwritten. I can see no problem with current behaviour. Am I missing sth?