Files
For disambiguation see also Computer file
Files are the eight vertical lines or columns of a Chessboard, labeled from 'A' to 'H', or 'a' to 'h'. Each file contains eight vertically arranged Squares of alternating white and black, or light and dark Color.
Contents
File Names
In a descriptive notation, files are also nominated by the Pieces from their initial position (similar to Pawns), like Rook-Files (a- and h-File, see diagram), Knight-Files (b- and g-File), Bishop-Files (c- and f-File), and Queen-File (d-File) and King-File (e-File), also called Center Files.
| abcdefgh | ||
| 8 7 6 5 4 3 2 1 | • • • • • • • • • • • • • • • • | 8 7 6 5 4 3 2 1 |
| abcdefgh |
Square Mapping Notes
Whether the square difference of neighbored squares on a rank or file is either 1 or 8, depends on the square mapping. We further rely on little-endian rank-file mapping, which keeps consecutive squares of a rank as neighbored elements in Memory (or register).
Square Difference
Within a 0..63 square index range and the mentioned square mapping (a1 = 0), the difference of two neighbored squares on a File is eight.
Enumeration
As mentioned, on a Chessboard the eight files are labeled from 'A' to 'H'. To make them zero based indices as appropriate for C like programming languages, we enumerate files from 0 to 7. Little-endian file-mapping (as used here) assigns the A-File to index zero. Three bits are required to enumerate from 0 to 7.
A little-endian file-mapping enumeration in C++ might look like this:
enum enumFile {
efAFile = 0,
efBFile = 1,
efCFile = 2,
efDFile = 3,
efEFile = 4,
efFFile = 5,
efGFile = 6,
efHFile = 7,
};
File from Square
Rank-File mapping of squares keeps the file as the three lower bits of a Square index.
file = square & 7; // modulo 8
File-Distance
The file-distance is the absolute difference between two files (their 0-7 indices). The maximum file-distance is 7.
fileDistance = abs (file1 - file2); fileDistance = abs (file2 - file1);
Two Squares on a File
Two Squares are on the same File, if their file distance is zero. The masking of the file bits can be done after the subtraction.
bool squaresOnSameFile(int sq1, int sq2) {
return ((sq2 - sq1) & 7) == 0;
}
The Symmetric difference aka xor is sufficent for the test as well [1]
bool squaresOnSameFile(int sq1, int sq2) {
return ((sq1 ^ sq2) & 7) == 0;
}
Pawns and Files
See also
References
- ↑ An undetected bug for 10 years by Oliver Brausch, CCC, August 18, 2020
