Promotion to bishop

[pedrox]

The reason is by design. Vas save the information of his moves in 16 bits, storing information of the promotion to bishop will require 32 bits.

[swami]

Are there any epds related to Underpromotion?

[BubbaTough]

Are there any epds related to Underpromotion?

I remember seeing a few in some Arasan test suites, including promotion to bishop. I think the main point is to make engine writers that waste a few elo on fully supporting under promotion feel better .

-Sam

[bob]

I have always wondered why Rybka cannot promote to bishop (while it accepts a bishop promotion). Is checking for this move so time-consuming that it isn't worth it? Does it make the code much more complex? Then why do all other engines do it?
Can it be that this thing has some big secret in it, maybe the reason of Rybka's great strength? Vasik has been attacked many times for the lack of bishop underpromotion but he stubbornly declined to implement it. But why?

An engine that is 100% faster is 50 Elo stronger.
An engine that is 10% faster is 5 Elo stronger.

Skipping bishop promotions makes Rybka 10% faster and gains 5 Elo points.

Matthias.

I don't believe it is worth 10%, I'll measure this later this afternoon and report actual results.

I tried this. Had to delete something like 9 lines of code to get rid of bishop underpromotions. I could measure absolutely no speed difference with or without. Even on positions like fine 70 which has massive promotion branches, the NPS did not vary by even 1%. I saw a few thousand nodes in a 1 minute search, typically, which did not produce a measurable speed increase.

[bob]

The reason is by design. Vas save the information of his moves in 16 bits, storing information of the promotion to bishop will require 32 bits.

Why would that matter? It is more efficient to use 32 bit values anyway...

[BubbaTough]

I have always wondered why Rybka cannot promote to bishop (while it accepts a bishop promotion). Is checking for this move so time-consuming that it isn't worth it? Does it make the code much more complex? Then why do all other engines do it?
Can it be that this thing has some big secret in it, maybe the reason of Rybka's great strength? Vasik has been attacked many times for the lack of bishop underpromotion but he stubbornly declined to implement it. But why?

An engine that is 100% faster is 50 Elo stronger.
An engine that is 10% faster is 5 Elo stronger.

Skipping bishop promotions makes Rybka 10% faster and gains 5 Elo points.

Matthias.

I don't believe it is worth 10%, I'll measure this later this afternoon and report actual results.

I tried this. Had to delete something like 9 lines of code to get rid of bishop underpromotions. I could measure absolutely no speed difference with or without. Even on positions like fine 70 which has massive promotion branches, the NPS did not vary by even 1%. I saw a few thousand nodes in a 1 minute search, typically, which did not produce a measurable speed increase.

I believe he actually meant there was a slight reduction in search time for a ply, mostly due to reduced tree size. It is not really a NPS issue.

-Sam

[michiguel]

The reason is by design. Vas save the information of his moves in 16 bits, storing information of the promotion to bishop will require 32 bits.

You mean that Rybka cannot promote to bishop even at the root? Is that so?
But, I do not think that should be the problem. You can have 16 bit move and promote to anything. Old programs did it.

Miguel

[Matthias Gemuh]

An engine that is 100% faster is 50 Elo stronger.
An engine that is 10% faster is 5 Elo stronger.

Skipping bishop promotions makes Rybka 10% faster and gains 5 Elo points.

Matthias.

I don't believe it is worth 10%, I'll measure this later this afternoon and report actual results.

I tried this. Had to delete something like 9 lines of code to get rid of bishop underpromotions. I could measure absolutely no speed difference with or without. Even on positions like fine 70 which has massive promotion branches, the NPS did not vary by even 1%. I saw a few thousand nodes in a 1 minute search, typically, which did not produce a measurable speed increase.

I believe he actually meant there was a slight reduction in search time for a ply, mostly due to reduced tree size. It is not really a NPS issue.

-Sam

Right. As I explained in one post, it is about a 10% smaller search tree, not 10% higher nps.
10% is a difficult-to-prove figure, except one really plays 100000 unique games or more.

[Matthias Gemuh]

The reason is by design. Vas save the information of his moves in 16 bits, storing information of the promotion to bishop will require 32 bits.

That sounds like best explanation so far. 16 bits and 32 bits move formats make quite a difference in hash useage and book size.

Matthias.

[Osipov Jury]

http://rybkaforum.net/cgi-bin/rybkaforu ... ?pid=10133