count_last_flip_plain.c File Reference

Functions
int	last_flip (int pos, unsigned long long P)

Variables
static const unsigned char	COUNT_FLIP [8][256]
static const unsigned long long	mask_d [2][64]

Detailed Description

A function is provided to count the number of fipped disc of the last move.

The basic principle is to read into an array a precomputed result. Doing this is easy for a single line ; as we can use arrays of the form:

• COUNT_FLIP[square where we play][8-bits disc pattern]. The problem is thus to convert any line of a 64-bits disc pattern into an 8-bits disc pattern. A fast way to do this is to select the right line, with a bit-mask, to gather the masked-bits into a continuous set by a simple multiplication and to right-shift the result to scale it into a number between 0 and 255. Once we get our 8-bits disc patterns, we directly get the number of flipped discs from the precomputed array, and add them from each flipping lines. For optimization purpose, the value returned is twice the number of flipped disc, to facilitate the computation of disc difference.

Date

1998 - 2017

Author

Richard Delorme

Toshihiko Okuhara

Version

4.4

Function Documentation

last_flip()

int last_flip	(	int	pos,
		unsigned long long	P )

Count last flipped discs when playing on the last empty.

Parameters

pos	the last empty square.
P	player's disc pattern.

Returns

flipped disc count.

Variable Documentation

COUNT_FLIP

const unsigned char COUNT_FLIP[8][256]

static

precomputed count flip array

mask_d

const unsigned long long mask_d[2][64]

static