y16t/lib/y16t_idx.h

// SPDX-License-Identifier: ISC
#pragma once
#include <inttypes.h>
#include <stddef.h>

typedef struct {
	int fd;
	// offset is in 4KiB units
	size_t offset;
} y16t_idx_t;

// try to lookup the given coordinates,
// and return the corresponding location via `result`.
// the file given as `fh` is expected to be at least 256KiB large
// returns a negative errno number in case of failure
__attribute__((nonnull))
int y16t_idx_lookup(
	y16t_idx_t  idx,
	uint8_t     x,
	uint8_t     y,
	uint32_t   *result
);

// update a table entry.
int y16t_idx_update(
	y16t_idx_t idx,
	uint8_t    x,
	uint8_t    y,
	uint32_t   newval
);

// insert a table entry if it doesn't already exist
int y16t_idx_get_or_insert(
	y16t_idx_t idx,
	uint8_t    x,
	uint8_t    y,
	uint32_t  *value,
	uint32_t (*palloc)(void*),
	void      *context
);

// iterate over columns or rows
int y16t_idx_foreach_x(
	y16t_idx_t idx,
	uint8_t    y,
	int      (*callback)(uint8_t, uint32_t, void*),
	void      *context
);

int y16t_idx_foreach_y(
	y16t_idx_t idx,
	uint8_t    χ,
	int      (*callback)(uint8_t, uint32_t, void*),
	void      *context
);