y16t/idx.c

// SPDX-License-Identifier: ISC
#include "y16t.h"
#include "y16t_internal.h"
#include <arpa/inet.h>
#include <errno.h>

static __attribute__((pure))
uint32_t y16t_table_at(const uint8_t x, const uint8_t y)
{
	return y16t_hilbert_xy2d(1 << 16, x, y) << 2;
}

int y16t_idx_lookup(
	FILE     *fh,
	uint8_t   x,
	uint8_t   y,
	uint32_t *result
) {
	const long key = y16t_table_at(x, y);

	if(key && fseek(fh, key, SEEK_CUR) == -1)
		return -EIO;
	if(fread(result, 4, 1, fh) != 1)
		return -EIO;
	*result = ntohl(*result);
	if(key && fseek(fh, -key, SEEK_CUR) == -1)
		return -EIO;

	return 0;
}

int y16t_idx_update(
	FILE           *fh,
	const uint8_t  x,
	const uint8_t  y,
	const uint32_t newval
) {
	const long key = y16t_table_at(x, y);
	const uint32_t odval = htonl(newval);

	if(key && fseek(fh, key, SEEK_CUR) == -1)
		return -EIO;
	if(fwrite(&odval, 4, 1, fh) != 1)
		return -EIO;
	if(key && fseek(fh, -key, SEEK_CUR) == -1)
		return -EIO;

	return 0;
}

int y16t_idx_foreach_x(
	FILE   *fh,
	uint8_t y,
	int   (*callback)(uint32_t, void*),
	void   *context
) {
	long offset = 0;

	for (uint16_t x = 0; x < 0xff; ++x) {
		uint32_t value = 0;
		const uint32_t key = y16t_table_at(x, y);
		const long delta = ((long)key) - offset;
		if(delta && fseek(fh, delta, SEEK_CUR) == -1)
			return -EIO;
		offset = key;
		if(fread(&value, 4, 1, fh) != 1)
			return -EIO;
		int tmp = callback(ntohl(value), context);
		if(tmp) return tmp;
	}

	if(offset && fseek(fh, -offset, SEEK_CUR) == -1)
		return -EIO;

	return 0;
}

int y16t_idx_foreach_y(
	FILE   *fh,
	uint8_t x,
	int   (*callback)(uint32_t, void*),
	void   *context
) {
	long offset = 0;

	for (uint16_t y = 0; y < 0xff; ++y) {
		uint32_t value = 0;
		const uint32_t key = y16t_table_at(x, y);
		const long delta = ((long)key) - offset;
		if(delta && fseek(fh, delta, SEEK_CUR) == -1)
			return -EIO;
		offset = key;
		if(fread(&value, 4, 1, fh) != 1)
			return -EIO;
		int tmp = callback(ntohl(value), context);
		if(tmp) return tmp;
	}

	if(offset && fseek(fh, -offset, SEEK_CUR) == -1)
		return -EIO;

	return 0;
}