finders.h

#ifndef FINDERS_H_
#define FINDERS_H_


#include "generator.h"


#ifdef __cplusplus
extern "C"
{
#endif

#define MASK48 (((int64_t)1 << 48) - 1)

enum StructureType
{
    Feature, // for locations of temple generation attempts pre 1.13
    Desert_Pyramid,
    Jungle_Temple, Jungle_Pyramid = Jungle_Temple,
    Swamp_Hut,
    Igloo,
    Village,
    Ocean_Ruin,
    Shipwreck,
    Monument,
    Mansion,
    Outpost,
    Ruined_Portal,
    Ruined_Portal_N,
    Ancient_City,
    Treasure,
    Mineshaft,
    Desert_Well,
    Geode,
    Fortress,
    Bastion,
    End_City,
    End_Gateway,
    End_Island,
    Trail_Ruins,
    Trial_Chambers,
    FEATURE_NUM
};


enum
{   // structure config property flags
    STRUCT_TRIANGULAR   = 0x01, // structure uses a triangular distribution
    STRUCT_CHUNK        = 0x02, // structure is checked for each chunk
    STRUCT_NETHER       = 0x10, // nether structure
    STRUCT_END          = 0x20, // end structure
};
// use getStructureConfig() for the version specific structure configuration
STRUCT(StructureConfig)
{
    int32_t salt;
    int8_t  regionSize;
    int8_t  chunkRange;
    uint8_t structType;
    uint8_t properties;
    float   rarity;
};


STRUCT(Pos)  { int x, z; };
STRUCT(Pos3) { int x, y, z; };


STRUCT(StrongholdIter)
{
    Pos pos;        // accurate location of current stronghold
    Pos nextapprox; // approxmimate location (+/-112 blocks) of next stronghold
    int index;      // stronghold index counter
    int ringnum;    // ring number for index
    int ringmax;    // max index within ring
    int ringidx;    // index within ring
    double angle;   // next angle within ring
    double dist;    // next distance from origin (in chunks)
    uint64_t rnds;  // random number seed (48 bit)
    int mc;         // minecraft version
};


STRUCT(StructureVariant)
{
    uint8_t abandoned   :1; // is zombie village
    uint8_t giant       :1; // giant portal variant
    uint8_t underground :1; // underground portal
    uint8_t airpocket   :1; // portal with air pocket
    uint8_t basement    :1; // igloo with basement
    uint8_t cracked     :1; // geode with crack
    uint8_t size;           // geode size | igloo middel pieces
    uint8_t start;          // starting piece index
    short   biome;          // biome variant
    uint8_t rotation;       // 0:0, 1:cw90, 2:cw180, 3:cw270=ccw90
    uint8_t mirror;
    int16_t x, y, z;
    int16_t sx, sy, sz;
};

STRUCT(Piece)
{
    const char *name;   // structure piece name
    Pos3 pos, bb0, bb1; // position and bounding box limits
    uint8_t rot;        // rotation
    int8_t depth;
    int8_t type;
    Piece *next;
};

STRUCT(EndIsland)
{
    int x, y, z;
    int r;
};

enum
{
    BF_APPROX       = 0x01, // enabled aggresive filtering, trading accuracy
    BF_FORCED_OCEAN = FORCE_OCEAN_VARIANTS,
};
STRUCT(BiomeFilter)
{
    // bitfields for biomes required at their respecive layers
    uint64_t tempsToFind; // Special (1:1024)
    uint64_t otempToFind; // OceanTemp (1:256)
    uint64_t majorToFind; // Biome (1:256)
    uint64_t edgesToFind; // Edge (1:64) [mod64: as special case for bamboo]
    // bitfields for biomes to find at RareBiome(1:64), Shore(1:16) and Mix(1:4)
    // layers for (biomeID < 64) and modified (biomeID >= 128 && biomeID < 192)
    uint64_t raresToFind, raresToFindM;
    uint64_t shoreToFind, shoreToFindM;
    uint64_t riverToFind, riverToFindM;
    uint64_t oceanToFind; // all required ocean types

    int specialCnt; // number of special temperature categories required

    uint32_t flags;

    // the biome exclusion aborts generation when the area contains no biomes
    // that can generate the excluded biomes
    uint64_t tempsToExcl;
    uint64_t majorToExcl;
    uint64_t edgesToExcl;
    uint64_t raresToExcl, raresToExclM;
    uint64_t shoreToExcl, shoreToExclM;
    uint64_t riverToExcl, riverToExclM;

    uint64_t biomeToExcl, biomeToExclM;
    uint64_t biomeToFind, biomeToFindM;
    uint64_t biomeToPick, biomeToPickM;
};


/***************************** Structure Positions *****************************
 *
 *  For most structure positions, Minecraft divides the world into a grid of
 *  regions (usually 32x32 chunks) and performs one generation attempt
 *  somewhere in each region. The position of this attempt is governed by the
 *  structure type, the region coordiates and the lower 48-bits of the world
 *  seed. The remaining top 16 bits do not influence structure positions.
 *  The dependency on the region coordinates is linear for both the X and Z
 *  directions, which means that the positions of most structures in a world
 *  can be translated by applying the following transformation to a seed:
 *
 *  seed2 = seed1 - dregX * 341873128712 - dregZ * 132897987541;
 *
 *  Here seed1 and seed2 have the same structure positioning, but moved by a
 *  region offset of (dregX,dregZ).
 *
 *  Another property of note is that seed1 at region (0,0) is simply the world
 *  seed plus a constant that is specific to the stucture type (its salt). This
 *  means that some structure types share quad-bases which are just offset by
 *  their respective salt differences.
 */

//==============================================================================
// Moving Structures
//==============================================================================

/* Transposes a base seed such that structures are moved by the specified region
 * vector, (regX, regZ).
 */
static inline uint64_t moveStructure(uint64_t baseSeed, int regX, int regZ)
{
    return (baseSeed - regX*341873128712 - regZ*132897987541) & 0xffffffffffff;
}


//==============================================================================
// Finding Structure Positions
//==============================================================================


/* Selects the structure configuration for a given version. Returns zero upon
 * failure (e.g. version does not support structure type).
 */
int getStructureConfig(int structureType, int mc, StructureConfig *sconf);

/* The library can be compiled to use a custom internal getter for structure
 * configurations. For this, the macro STRUCT_CONFIG_OVERRIDE should be defined
 * as true and the function getStructureConfig_override() should be defined
 * with a custom function body. However, note this is experimental and not all
 * structure configs may work. (Ideally only change structure salts.)
 */
#if STRUCT_CONFIG_OVERRIDE
int getStructureConfig_override(int stype, int mc, StructureConfig *sconf);
#endif

/* Finds the block position of the structure generation attempt in a given
 * region. You can use isViableStructurePos() to test if the necessary biome
 * requirements are met for the structure to actually generate at that position.
 * Some structure types may fail to produce a valid position in the given
 * region regardless of biomes, in which case the function returns zero.
 *
 * @structureType   : structure type
 * @mc              : minecraft version
 * @seed            : world seed (only the lower 48-bits are relevant)
 * @regX,regZ       : region coordinates (the region size depends on type)
 * @pos             : output block position
 *
 * Returns zero if the position is invalid, or non-zero otherwise.
 */
int getStructurePos(int structureType, int mc, uint64_t seed, int regX, int regZ, Pos *pos);

/* The inline functions below get the generation attempt position given a
 * structure configuration. Most small structures use the getFeature..
 * variants, which have a uniform distribution, while large structures
 * (monuments and mansions) have a triangular distribution.
 */
static inline ATTR(const)
Pos getFeaturePos(StructureConfig config, uint64_t seed, int regX, int regZ);

static inline ATTR(const)
Pos getFeatureChunkInRegion(StructureConfig config, uint64_t seed, int regX, int regZ);

static inline ATTR(const)
Pos getLargeStructurePos(StructureConfig config, uint64_t seed, int regX, int regZ);

static inline ATTR(const)
Pos getLargeStructureChunkInRegion(StructureConfig config, uint64_t seed, int regX, int regZ);

/* Checks a chunk area, starting at (chunkX, chunkZ) with size (chunkW, chunkH)
 * for Mineshaft positions. If not NULL, positions are written to the buffer
 * 'out' up to a maximum number of 'nout'. The return value is the number of
 * chunks with Mineshafts in the area.
 */
int getMineshafts(int mc, uint64_t seed, int chunkX, int chunkZ,
        int chunkW, int chunkH, Pos *out, int nout);

// not exacly a structure
static inline ATTR(const)
int isSlimeChunk(uint64_t seed, int chunkX, int chunkZ)
{
    uint64_t rnd = seed;
    rnd += (int)(chunkX * 0x5ac0db);
    rnd += (int)(chunkX * chunkX * 0x4c1906);
    rnd += (int)(chunkZ * 0x5f24f);
    rnd += (int)(chunkZ * chunkZ) * 0x4307a7ULL;
    rnd ^= 0x3ad8025fULL;
    setSeed(&rnd, rnd);
    return nextInt(&rnd, 10) == 0;
}

/* Finds the position and size of the small end islands in a given chunk.
 * Returns the number of end islands found.
 */
int getEndIslands(EndIsland islands[2], int mc, uint64_t seed, int chunkX, int chunkZ);

/* Finds the small end islands in the given area and updates the existing
 * height map, y, accordingly. Note that values in the y-map can only increase
 * using this.
 */
int mapEndIslandHeight(float *y, const EndNoise *en, uint64_t seed,
    int x, int z, int w, int h, int scale);

/* Checks if the given chunk contains no blocks. This included a check for
 * small end islands.
 */
int isEndChunkEmpty(const EndNoise *en, const SurfaceNoise *sn, uint64_t seed,
    int chunkX, int chunkZ);

//==============================================================================
// Finding Strongholds and Spawn
//==============================================================================

/* Finds the approximate location of the first stronghold (+/-112 blocks),
 * which can be determined from the lower 48 bits of the world seed without
 * biome checks. If 'sh' is not NULL, it will be initialized for iteration
 * using nextStronghold() to get the accurate stronghold locations, as well as
 * the subsequent approximate stronghold positions.
 *
 * @sh      : stronghold iterator to be initialized (nullable)
 * @mc      : minecraft version
 * @s48     : world seed (only 48-bit are relevant)
 *
 * Returns the approximate block position of the first stronghold.
 */
Pos initFirstStronghold(StrongholdIter *sh, int mc, uint64_t s48);

/* Performs the biome checks for the stronghold iterator and finds its accurate
 * location, as well as the approximate location of the next stronghold.
 *
 * @sh      : stronghold iteration state, holding position info
 * @g       : generator, should be initialized for Overworld generation,
 *            for version 1.19.3+ the generator may be left NULL to iterate
 *            over the approximate locations without biome check
 *
 * Returns the number of further strongholds after this one.
 */
int nextStronghold(StrongholdIter *sh, const Generator *g);


/* Finds the approximate spawn point in the world.
 * The random state 'rng' output can be NULL to ignore.
 */
Pos estimateSpawn(const Generator *g, uint64_t *rng);

/* Finds the spawn point in the world.
 * Warning: Slow, and may be inaccurate because the world spawn depends on
 * grass blocks!
 */
Pos getSpawn(const Generator *g);


/* Finds a suitable pseudo-random location in the specified area.
 * This function is used to determine the positions of spawn and strongholds.
 * Warning: accurate, but slow!
 *
 * @g           : generator for Overworld biomes
 * @x,y,z       : origin for the search
 * @radius      : square 'radius' of the search
 * validB       : valid biomes, as a bitset for biomes with 0 <= id < 64
 * validM       : valid biomes, as a bitset for biomes with 192 <= id < 256
 * @rnd         : random obj, initialise using setSeed(rnd, world_seed)
 * @passes      : (output) number of valid biomes passed, NULL to ignore
 */
Pos locateBiome(
        const Generator *g, int x, int y, int z, int radius,
        uint64_t validB, uint64_t validM, uint64_t *rng, int *passes);

/* Get the shadow seed.
 */
static inline uint64_t getShadow(uint64_t seed)
{
    return -7379792620528906219LL - seed;
}



//==============================================================================
// Validating Structure Positions
//==============================================================================

/* Performs a biome check near the specified block coordinates to determine
 * whether a structure of the given type could spawn there. You can get the
 * block positions using getStructurePos().
 * The generator, 'g', should be initialized for the correct MC version,
 * dimension and seed. The generator may be temporarily modified during the
 * function call, but will be restored upon return.
 * The 'flags' argument is optional structure specific information, such as the
 * biome variant for villages.
 */
int isViableStructurePos(int structType, Generator *g, int blockX, int blockZ, uint32_t flags);

/* Checks if the specified structure type could generate in the given biome.
 */
int isViableFeatureBiome(int mc, int structureType, int biomeID);

/* Some structures in 1.18 now only spawn if the surface is sufficiently high
 * at all four bounding box corners. This affects primarily Desert_Pyramids,
 * Jungle_Temples and Mansions.
 * Currently cubiomes does not provide overworld surface height and cannot
 * check it, but we can rule out some unlikely positions based biomes.
 *
 * This function is meant only for the 1.18 Overworld and is subject to change.
 */
int isViableStructureTerrain(int structType, Generator *g, int blockX, int blockZ);

/* End Cities require a sufficiently high surface in addition to a biome check.
 * The world seed should be applied to the EndNoise and SurfaceNoise before
 * calling this function. (Use initSurfaceNoiseEnd() for initialization.)
 */
int isViableEndCityTerrain(const Generator *g, const SurfaceNoise *sn,
        int blockX, int blockZ);


//==============================================================================
// Finding Properties of Structures
//==============================================================================

/* Initialises and returns a random seed used in the (16x16) chunk generation.
 * This random object is used for recursiveGenerate() which is responsible for
 * generating caves, ravines, mineshafts, and virtually all other structures.
 */
inline static
uint64_t chunkGenerateRnd(uint64_t worldSeed, int chunkX, int chunkZ)
{
    uint64_t rnd;
    setSeed(&rnd, worldSeed);
    rnd = (nextLong(&rnd) * chunkX) ^ (nextLong(&rnd) * chunkZ) ^ worldSeed;
    setSeed(&rnd, rnd);
    return rnd;
}

/* Get data, such as rotation and bounding box of a structure instance.
 * (Supports only some structure types.)
 */
int getVariant(StructureVariant *sv, int structType, int mc, uint64_t seed,
        int blockX, int blockZ, int biomeID);

/* Generate the structure pieces of an End City. This pieces buffer should be
 * large enough to hold END_CITY_PIECES_MAX elements.
 * @pieces          : output buffer
 * @seed            : world seed
 * @chunkX, chunkZ  : 16x16 chunk position
 *
 * Returns the number of structure pieces generated.
 */
int getEndCityPieces(Piece *pieces, uint64_t seed, int chunkX, int chunkZ);
enum
{   // End City piece types
    BASE_FLOOR,
    BASE_ROOF,
    BRIDGE_END,
    BRIDGE_GENTLE_STAIRS,
    BRIDGE_PIECE,
    BRIDGE_STEEP_STAIRS,
    FAT_TOWER_BASE,
    FAT_TOWER_MIDDLE,
    FAT_TOWER_TOP,
    SECOND_FLOOR_1,
    SECOND_FLOOR_2,
    SECOND_ROOF,
    END_SHIP,
    THIRD_FLOOR_1,
    THIRD_FLOOR_2,
    THIRD_ROOF,
    TOWER_BASE,
    TOWER_FLOOR, // unused
    TOWER_PIECE,
    TOWER_TOP,
    END_CITY_PIECES_MAX = 421
};

/* Generate the structure pieces of a Nether Fortress. The maximum number of
 * pieces that are generated is limited to 'n'. A buffer length of around 400
 * should be sufficient in practice, but a fortress can in theory contain many
 * more than that. The number of generated pieces is given by the return value.
 */
int getFortressPieces(Piece *list, int n, int mc, uint64_t seed, int chunkX, int chunkZ);
enum
{   // Fortress piece types
    FORTRESS_START,
    BRIDGE_STRAIGHT,
    BRIDGE_CROSSING,
    BRIDGE_FORTIFIED_CROSSING,
    BRIDGE_STAIRS,
    BRIDGE_SPAWNER,
    BRIDGE_CORRIDOR_ENTRANCE,
    CORRIDOR_STRAIGHT,
    CORRIDOR_CROSSING,
    CORRIDOR_TURN_RIGHT,
    CORRIDOR_TURN_LEFT,
    CORRIDOR_STAIRS,
    CORRIDOR_T_CROSSING,
    CORRIDOR_NETHER_WART,
    FORTRESS_END,
    PIECE_COUNT,
};

/* Find the 20 fixed inner positions where End Gateways generate upon defeating
 * the Dragon. The positions are written to 'src' in generation order.
 */
void getFixedEndGateways(int mc, uint64_t seed, Pos src[20]);

/* Get the outer linked Gateway destination for an inner source Gateway.
 * (mc > MC_1_12)
 */
Pos getLinkedGatewayChunk(const EndNoise *en, const SurfaceNoise *sn,
    uint64_t seed, Pos src, Pos *dst);
Pos getLinkedGatewayPos(const EndNoise *en, const SurfaceNoise *sn,
    uint64_t seed, Pos src);


/* Find the number of each type of house that generate in a village
 * (mc < MC_1_14)
 * @housesOut       : output number of houses for each entry in the house type
 *                    enum (i.e this should be an array of length HOUSE_NUM)
 * @seed            : world seed
 * @chunkX, chunkZ  : 16x16 chunk position of the village origin
 *
 * Returns the random object seed after finding these numbers.
 */
enum
{
    HouseSmall, Church, Library, WoodHut, Butcher, FarmLarge, FarmSmall,
    Blacksmith, HouseLarge, HOUSE_NUM
};
uint64_t getHouseList(int *houses, uint64_t seed, int chunkX, int chunkZ);



//==============================================================================
// Seed Filters (generic)
//==============================================================================


/* Add the given biome 'id' to a biome set which is represented by the
 * bitfields mL and mM for ids 0-63 and 128-191, respectively.
 */
static inline void idSetAdd(uint64_t *mL, uint64_t *mM, int id)
{
    switch (id & ~0x3f) {
    case 0:     *mL |= 1ULL << id;       break; // [0, 64)
    case 128:   *mM |= 1ULL << (id-128); break; // [128, 192)
    }
}

static inline int idSetTest(uint64_t mL, uint64_t mM, int id)
{
    switch (id & ~0x3f) {
    case 0:     return !!(mL & (1ULL << id));       // [0, 64)
    case 128:   return !!(mM & (1ULL << (id-128))); // [128, 192)
    }
    return 0;
}

/* Samples biomes within the specified range and checks that at least a given
 * proportion of the biomes in that area evaluate as successes.
 *
 * @g           : biome generator
 * @r           : range to be checked
 * @rng         : random number seed for the sampling positions
 * @coverage    : minimum coverage of successful evaluations, [0,1]
 * @confidence  : confidence level, (0,1), e.g. 0.95 for a 95% confidence
 * @eval        : evaluation function - 0:fail, 1:success, -1:skip, else:abort
 * @data        : data argument for eval()
 *
 * Returns non-zero if a sufficient proportion of the sampled positions
 * evaluted as successes.
 */
int monteCarloBiomes(
        Generator         * g,
        Range               r,
        uint64_t          * rng,
        double              coverage,
        double              confidence,
        int (*eval)(Generator *g, int scale, int x, int y, int z, void *data),
        void              * data
        );


//==============================================================================
// Seed Filters (for versions up to 1.17)
//==============================================================================


/* Creates a biome filter configuration from a given list of required and
 * excluded biomes. Biomes should not appear in both lists. Lists of length
 * zero may be passed as null.
 */
void setupBiomeFilter(
    BiomeFilter *bf,
    int mc, uint32_t flags,
    const int *required, int requiredLen,
    const int *excluded, int excludedLen,
    const int *matchany, int matchanyLen);

/* Starts to generate the specified range and checks if the biomes meet the
 * requirements of the biome filter, returning either:
 * 0 (failed),
 * 1 (okay, area is fully generated), or
 * 2 (okay, incomplete generation).
 *
 * The area will be generated inside the cache (if != NULL) but is only
 * defined if the generation was fully completed (check return value).
 * More aggressive filtering can be enabled with the flags which may yield
 * some false negatives in exchange for speed.
 *
 * The generator should be set up for the correct version, however the
 * dimension and seed will be applied internally. This will modify the
 * generator into a partially initialized state that is not valid to use
 * outside this function without re-applying a seed.
 *
 * @g           : biome generator
 * @cache       : working buffer and output (nullable)
 * @r           : range to be checked
 * @dim         : dimension (0:Overworld, -1:Nether, +1:End)
 * @seed        : world seed
 * @filter      : biome requirements to be met
 * @flags       : enables features (see below)
 * @stop        : occasional check for abort (nullable)
 */
int checkForBiomes(
        Generator         * g,
        int               * cache,
        Range               r,
        int                 dim,
        uint64_t            seed,
        const BiomeFilter * filter,
        volatile char     * stop // should be atomic, but is fine as stop flag
        );

/* Specialization of checkForBiomes() for a LayerStack, i.e. the Overworld up
 * to 1.17.
 *
 * @ls          : layered generator (will be modified!)
 * @entry       : generation entry point (setLayerSeed() may be applied here)
 * @cache       : working buffer, and output (if != NULL)
 * @seed        : world seed
 * @x,z,w,h     : requested area
 * @filter      : biomes to be checked for
 */
int checkForBiomesAtLayer(
        LayerStack        * ls,
        Layer             * entry,
        int               * cache,
        uint64_t            seed,
        int                 x,
        int                 z,
        unsigned int        w,
        unsigned int        h,
        const BiomeFilter * filter
        );

/* Checks that the area (x,z,w,h) at layer Special, scale 1:1024 contains the
 * temperature category requirements defined by 'tc' as:
 * if (tc[TEMP_CAT] >= 0) require at least this many entries of this category
 * if (tc[TEMP_CAT] <  0) avoid, there shall be no entries of this category
 * TEMP_CAT is any of:
 * Oceanic, Warm, Lush, Cold, Freeing, Special+Warm, Special+Lush, Special+Cold
 * For 1.7-1.17 only.
 */
int checkForTemps(LayerStack *g, uint64_t seed, int x, int z, int w, int h, const int tc[9]);

/* Find the center positions for a given biome id.
 * @pos     : output biome center positions
 * @siz     : output size of biomes (nullable)
 * @nmax    : maximum number of output entries
 * @g       : generator, should be initialized for overworld generation
 * @r       : area to examine, requires: scale = 4, sy = 1
 * @match   : biome id to find
 * @minsiz  : minimum size of output biomes
 * @tol     : border tolerance
 * @stop    : stopping flag (nullable)
 * Returns the number of entries written to pos and siz.
 */
int getBiomeCenters(
        Pos           * pos,
        int           * siz,
        int             nmax,
        Generator     * g,
        Range           r,
        int             match,
        int             minsiz,
        int             tol,
        volatile char * stop
        );

/* Checks if a biome may generate given a version and layer ID as entry point.
 * The supported layers are:
 * L_BIOME_256, L_BAMBOO_256, L_BIOME_EDGE_64, L_HILLS_64, L_SUNFLOWER_64,
 * L_SHORE_16, L_RIVER_MIX_4, L_OCEAN_MIX_4, L_VORONOI_1
 * (provided the version matches)
 */
int canBiomeGenerate(int layerId, int mc, uint32_t flags, int biomeID);

/* Given a 'biomeID' at a generation 'layerId', this functions finds which
 * biomes may generate from it. The result is stored in the bitfields:
 * mL : for ids 0-63
 * mM : for ids 128-191
 */
void genPotential(uint64_t *mL, uint64_t *mM, int layerId, int mc, uint32_t flags, int biomeID);

/* Gets the biomes that can generate in the given version and layer ID.
 * In contrast to canBiomeGenerate() and genPotential() it also supports
 * L_OCEAN_TEMP_256 and 1.18+, where the layerId is ignored.
 * mL : for ids 0-63
 * mM : for ids 128-191
 */
void getAvailableBiomes(uint64_t *mL, uint64_t *mM, int layerId, int mc, uint32_t flags);

//==============================================================================
// Biome Noise Finders (for 1.18+)
//==============================================================================

/**
 * Runs a gradient descent towards the minimum of the noise parameter times a
 * given factor. The algorithm is restricted to the area (x,z,w,h) and starts
 * at (i0,j0) relative to (x,z). The iteration is terminated when either
 * 1) a fix point has been reached,
 * 2) maxiter iterations have been completed,
 * 3) or the sampling position has moved more than maxrad away from (i0,j0).
 *
 * Alpha is an optimization argument that is used to determine the length of
 * large steps based on the current gradient.
 *
 * Optionally, the iteration can also call the custom function:
 *  func(data, x, z, factor*para_noise(x,z));
 *
 * The return value is the minimum value reached.
 */
double getParaDescent(const DoublePerlinNoise *para, double factor,
    int x, int z, int w, int h, int i0, int j0, int maxrad,
    int maxiter, double alpha, void *data, int (*func)(void*,int,int,double));

/**
 * Determines the value range of a climate noise parameter over the given area.
 * The sampling has scale 1:4 and sampling shift is not considered, so biomes
 * could potentially *leak* in at the boarders.
 * An optional function:
 *  func(data, x, z, climate_noise(x,z))
 * is called in each gradient descent iteration. If this function returns
 * non-zero the search is aborted, the results are undefined and a non-zero
 * error is returned.
 *
 * The results are written to pmin and pmax (which would be cast to an integer
 * during boime mapping). Nullable, to look for minima and maxima separately.
 */
int getParaRange(const DoublePerlinNoise *para, double *pmin, double *pmax,
    int x, int z, int w, int h, void *data, int (*func)(void*,int,int,double));

/**
 * Gets the min/max parameter values within which a biome change can occur.
 */
const int *getBiomeParaExtremes(int mc);

/**
 * Gets the min/max possible noise parameter values at which the given biome
 * can generate. The values are in min/max pairs in order of:
 * temperature, humidity, continentalness, erosion, depth, weirdness.
 */
const int *getBiomeParaLimits(int mc, int id);

/**
 * Determines which biomes are able to generate given a set of climate
 * parameter limits. Possible biomes are marked non-zero in the 'ids'.
 */
void getPossibleBiomesForLimits(char ids[256], int mc, int limits[6][2]);

/**
 * Find the largest rectangle in ids[sx][sz] which consists only of 'match'.
 * The limit corners are written to p0 and p1. Returned is the rectangle's area.
 */
int getLargestRec(int match, const int *ids, int sx, int sz, Pos *p0, Pos *p1);

//==============================================================================
// Implementaions for Functions that Ideally Should be Inlined
//==============================================================================


static inline ATTR(const)
Pos getFeatureChunkInRegion(StructureConfig config, uint64_t seed, int regX, int regZ)
{
    /*
    // Vanilla like implementation.
    setSeed(&seed, regX*341873128712 + regZ*132897987541 + seed + config.salt);

    Pos pos;
    pos.x = nextInt(&seed, 24);
    pos.z = nextInt(&seed, 24);
    */
    Pos pos;
    const uint64_t K = 0x5deece66dULL;
    const uint64_t M = (1ULL << 48) - 1;
    const uint64_t b = 0xb;

    // set seed
    seed = seed + regX*341873128712ULL + regZ*132897987541ULL + config.salt;
    seed = (seed ^ K);
    seed = (seed * K + b) & M;

    uint64_t r = config.chunkRange;
    if (r & (r-1))
    {
        pos.x = (int)(seed >> 17) % r;
        seed = (seed * K + b) & M;
        pos.z = (int)(seed >> 17) % r;
    }
    else
    {
        // Java RNG treats powers of 2 as a special case.
        pos.x = (int)((r * (seed >> 17)) >> 31);
        seed = (seed * K + b) & M;
        pos.z = (int)((r * (seed >> 17)) >> 31);
    }

    return pos;
}

static inline ATTR(const)
Pos getFeaturePos(StructureConfig config, uint64_t seed, int regX, int regZ)
{
    Pos pos = getFeatureChunkInRegion(config, seed, regX, regZ);

    pos.x = (int)(((uint64_t)regX*config.regionSize + pos.x) << 4);
    pos.z = (int)(((uint64_t)regZ*config.regionSize + pos.z) << 4);
    return pos;
}

static inline ATTR(const)
Pos getLargeStructureChunkInRegion(StructureConfig config, uint64_t seed, int regX, int regZ)
{
    Pos pos;
    const uint64_t K = 0x5deece66dULL;
    const uint64_t M = (1ULL << 48) - 1;
    const uint64_t b = 0xb;

    //TODO: power of two chunk ranges...

    // set seed
    seed = seed + regX*341873128712ULL + regZ*132897987541ULL + config.salt;
    seed = (seed ^ K);

    seed = (seed * K + b) & M;
    pos.x = (int)(seed >> 17) % config.chunkRange;
    seed = (seed * K + b) & M;
    pos.x += (int)(seed >> 17) % config.chunkRange;

    seed = (seed * K + b) & M;
    pos.z = (int)(seed >> 17) % config.chunkRange;
    seed = (seed * K + b) & M;
    pos.z += (int)(seed >> 17) % config.chunkRange;

    pos.x >>= 1;
    pos.z >>= 1;

    return pos;
}

static inline ATTR(const)
Pos getLargeStructurePos(StructureConfig config, uint64_t seed, int regX, int regZ)
{
    Pos pos = getLargeStructureChunkInRegion(config, seed, regX, regZ);

    pos.x = (int)(((uint64_t)regX*config.regionSize + pos.x) << 4);
    pos.z = (int)(((uint64_t)regZ*config.regionSize + pos.z) << 4);
    return pos;
}



#ifdef __cplusplus
}
#endif

#endif // FINDERS_H_