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Dann Corbit

Joined: 08 Mar 2006
Posts: 5125
Location: Redmond, WA USA

Post subject: Re: fen to fen functions    Posted: Tue May 22, 2007 6:33 pm

Uri Blass wrote:
Alessandro Scotti wrote:
Just a wild shot:

 Code: void fen2fen( char * fen, char * buf ) {     for( char * e = strchr(fen,' ') - 1; e >= fen; e-- ) {         *buf++ = *e ^ (isalpha(*e) ? 0x20 : 0x00);     }     strcpy( buf, strchr(fen,' ') ); }

If I understand correctly you try both to replace the side to move and replace the files of the pieces so a1 goes to h8 in this code.

This code also does not replace the side to move that is part of the fen
and it also is not correct for castling because there are order rules
and you need to write KQkq in this order and kqKQ is not correct fen.

This code is clearly shorter than my code.
I did not know the trick of xoring with 0x20 to make big letters small letters and the opposite.

I wrote so far code only for the case of changing side that is always possible and not for the case of left-right symmetry that may be impossible in case of castling rights(unless you use FRC and not normal chess and in that case left-right symmetry is always possible)

I did not go from the end to the beginning of the string and simply saved an array of strings for every rank of the board when later I used strncat to make from them one string(I have a special function to change one line when I do not need to change the order but only change big letters to small letters and the opposite).

I did not check that your code works but

I can make my code shorter based on the idea that you gave here but I do not think that it is important.

Uri

The xor trick relies upon the ASCII character set where 'A' is 0x41 and 'a' is 0x61 up to 'Z' is 0x5A and 'z' is 0x7A.

You can make reversing case more plain with:
foo = isupper(foo) ? tolower(foo) : toupper(foo);

Note that the toupper() and tolower() macros/functions do nothing if the input integer is not an alphabetic letter.
 Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First
Subject Author Date/Time
Uri Blass Mon May 21, 2007 10:17 am
Alessandro Scotti Mon May 21, 2007 3:20 pm
Reinhard Scharnagl Mon May 21, 2007 5:10 pm
Uri Blass Tue May 22, 2007 1:21 pm
Alessandro Scotti Tue May 22, 2007 3:46 pm
Uri Blass Tue May 22, 2007 4:24 pm
Alessandro Scotti Tue May 22, 2007 4:46 pm
Uri Blass Thu May 24, 2007 12:52 pm
Uri Blass Thu May 24, 2007 4:51 pm
Uri Blass Thu May 24, 2007 8:13 pm
Steffan Westcott Sat Jun 02, 2007 5:05 pm
Re: fen to fen functions Dann Corbit Tue May 22, 2007 6:33 pm
Dann Corbit Mon May 21, 2007 5:48 pm

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