Rotated Bitmaps,a New Twist on an Old Idea

Abstract

This paper describes some developments related to using bitmaps (64-bit integers using one bit for each square of the chessboard). In late 1994, after the ACM computer-chess event in Cape May, New Jersey, I decided to embark on a complete replacement chess program for CRAY BLITZ. I was interested in using the bitmap approach mentioned by Slate and Atkin in CHESS 4.x to determine for myself whether this approach was suitable for chess or not. In developing this new program, the concept of rotated bitmaps was developed, and this turned out to be what was needed to make this type of data structure produce reasonable performance.