// SPDX-License-Identifier: ISC
// this file is directly included by idx.c
// conversion between hilbert curve distance and x,y values

#include <inttypes.h>

// rotate/flip a quadrant appropriately
static void y16t_hilbert_rot(
	uint32_t n,
	uint32_t *x,
	uint32_t *y,
	uint32_t rx,
	uint32_t ry
) {
	if (ry == 0) {
		if (rx == 1) {
			*x = n-1 - *x;
			*y = n-1 - *y;
		}

		//Swap x and y
		uint32_t t = *x;
		*x = *y;
		*y = t;
	}
}

__attribute__((pure))
static uint32_t y16t_hilbert_xy2d(uint32_t n, uint32_t x, uint32_t y) {
	uint32_t rx, ry, s, d=0;
	for (s=n/2; s>0; s/=2) {
		rx = (x & s) > 0;
		ry = (y & s) > 0;
		d += s * s * ((3 * rx) ^ ry);
		y16t_hilbert_rot(n, &x, &y, rx, ry);
	}
	return d;
}

/*
static void y16t_hilbert_d2xy(uint32_t n, uint32_t d, uint32_t *x, uint32_t *y) {
	uint32_t rx, ry, s, t=d;
	*x = *y = 0;
	for (s=1; s<n; s*=2) {
		rx = 1 & (t/2);
		ry = 1 & (t ^ rx);
		y16t_hilbert_rot(s, x, y, rx, ry);
		*x += s * rx;
		*y += s * ry;
		t /= 4;
	}
}
*/