Distances.hpp

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/*
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#pragma once
 
#include <algorithm>
#include <libchess/board/BitboardIndex.hpp>
#include <libchess/board/Square.hpp>
#include <utility>
 
namespace chess::board {


[[nodiscard, gnu::const]] constexpr auto file_distance(
    const Square& first, const Square& second) noexcept
    -> BitboardIndex;

[[nodiscard, gnu::const]] constexpr auto rank_distance(
    const Square& first, const Square& second) noexcept
    -> BitboardIndex;

[[nodiscard, gnu::const]] constexpr auto are_on_same_diagonal(
    const Square& first, const Square& second) noexcept
    -> bool;

[[nodiscard, gnu::const]] constexpr auto manhattan_distance(
    const Square& first, const Square& second) noexcept
    -> BitboardIndex;

[[nodiscard, gnu::const]] constexpr auto center_manhattan_distance(
    const Square& square) noexcept
    -> BitboardIndex;

[[nodiscard, gnu::const]] constexpr auto chebyshev_distance(
    const Square& first, const Square& second) noexcept
    -> BitboardIndex;

[[nodiscard, gnu::const]] auto knight_distance(
    const Square& first, const Square& second)
    -> BitboardIndex;

 
/*
                         ___                           ,--,
      ,---,            ,--.'|_                ,--,   ,--.'|
    ,---.'|            |  | :,'             ,--.'|   |  | :
    |   | :            :  : ' :             |  |,    :  : '    .--.--.
    |   | |   ,---.  .;__,'  /    ,--.--.   `--'_    |  ' |   /  /    '
  ,--.__| |  /     \ |  |   |    /       \  ,' ,'|   '  | |  |  :  /`./
 /   ,'   | /    /  |:__,'| :   .--.  .-. | '  | |   |  | :  |  :  ;_
.   '  /  |.    ' / |  '  : |__  \__\/: . . |  | :   '  : |__ \  \    `.
'   ; |:  |'   ;   /|  |  | '.'| ," .--.; | '  : |__ |  | '.'| `----.   \
|   | '/  ''   |  / |  ;  :    ;/  /  ,.  | |  | '.'|;  :    ;/  /`--'  /__  ___  ___
|   :    :||   :    |  |  ,   /;  :   .'   \;  :    ;|  ,   /'--'.     /  .\/  .\/  .\
 \   \  /   \   \  /    ---`-' |  ,     .-./|  ,   /  ---`-'   `--'---'\  ; \  ; \  ; |
  `----'     `----'             `--`---'     ---`-'                     `--" `--" `--"
 
 */
 
constexpr auto file_distance(
    const Square& first, const Square& second) noexcept
    -> BitboardIndex
{
    const auto firstFile  = std::to_underlying(first.file);
    const auto secondFile = std::to_underlying(second.file);
 
    const auto [minFile, maxFile] = std::minmax(firstFile, secondFile);
 
    return static_cast<BitboardIndex>(maxFile - minFile);
}
 
constexpr auto rank_distance(
    const Square& first, const Square& second) noexcept
    -> BitboardIndex
{
    const auto firstRank  = std::to_underlying(first.rank);
    const auto secondRank = std::to_underlying(second.rank);
 
    const auto [minRank, maxRank] = std::minmax(firstRank, secondRank);
 
    return static_cast<BitboardIndex>(maxRank - minRank);
}
 
constexpr auto are_on_same_diagonal(
    const Square& first, const Square& second) noexcept
    -> bool
{
    return std::cmp_equal(file_distance(first, second), rank_distance(first, second));
}
 
constexpr auto manhattan_distance(
    const Square& first, const Square& second) noexcept
    -> BitboardIndex
{
    return static_cast<BitboardIndex>(file_distance(first, second) + rank_distance(first, second));
}
 
constexpr auto center_manhattan_distance(
    const Square& square) noexcept
    -> BitboardIndex
{
    auto file = static_cast<int>(square.file);
    auto rank = static_cast<int>(square.rank);
 
    file ^= (file - 4) >> 8;
    rank ^= (rank - 4) >> 8;
 
    return static_cast<BitboardIndex>((file + rank) & 7);
}
 
constexpr auto chebyshev_distance(
    const Square& first, const Square& second) noexcept
    -> BitboardIndex
{
    const auto fileDist = file_distance(first, second);
    const auto rankDist = rank_distance(first, second);
 
    return std::max(fileDist, rankDist);
}
 
} // namespace chess::board