Board.h File Reference

Bitboard-based representation of a Connect-4 position. More...

#include <array>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <map>
#include <random>
#include <sstream>
#include <vector>
#include "MoveList.h"

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Classes
class	BitBully::Board
	Connect-4 position represented as a pair of 64-bit bitboards. More...
struct	BitBully::Board::RawState
	Plain-data snapshot of the board's internal state. More...

Namespaces
namespace	BitBully
	Top-level namespace for the BitBully Connect-4 engine.

Macros
#define	uint64_t_popcnt   popCountBoard
	Portable fallback popcount when no compiler intrinsic is available.

Functions
int	ctz_u64 (uint64_t x)
	Count trailing zero bits of a 64-bit integer.
std::vector< int >	bits_set (uint64_t x)
	Decompose a bitboard into the indices of its set bits.

Variables
constexpr int	BitBully::CHAR_BIT = 8
	Number of bits per byte (defined locally if not provided by the platform).

Detailed Description

Bitboard-based representation of a Connect-4 position.

Defines the BitBully::Board class together with a handful of compile-time helpers (bit masks, popcount, count-trailing-zeros) used by the solver. The encoding follows the "split bitboard" scheme made popular by John Tromp's Fhourstones: a single 64-bit word holds all occupied cells of a 7×6 grid, plus an extra "sentinel" row that is never set during play but is used to detect overflowing column appends in constant time.

See also

https://github.com/qu1j0t3/fhourstones

Definition in file Board.h.

Macro Definition Documentation

uint64_t_popcnt

#define uint64_t_popcnt   popCountBoard

Portable fallback popcount when no compiler intrinsic is available.

Definition at line 50 of file Board.h.

Function Documentation

bits_set()

std::vector< int > bits_set ( uint64_t x )

inline

Decompose a bitboard into the indices of its set bits.

Walks the input from the least to the most significant bit, clearing one bit at a time using x &= x - 1. The result is sorted in ascending bit order.

Parameters

x	Bitboard whose set bits should be enumerated.

Returns

Vector of bit indices (0…63), one per set bit in x.

Definition at line 93 of file Board.h.

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ctz_u64()

int ctz_u64 ( uint64_t x )

inline

Count trailing zero bits of a 64-bit integer.

Returns the bit index of the least significant set bit. The function uses the most efficient implementation available for the current toolchain (_BitScanForward64 on MSVC, __builtin_ctzll on GCC/Clang) and falls back to a portable loop otherwise.

Parameters

x	Non-zero 64-bit input. Calling with x == 0 is undefined for the intrinsic variants.

Returns

Zero-based index of the least significant set bit.

Definition at line 66 of file Board.h.

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