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Hilbert and quadkey 128-bit encodings are reversible

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This commit is contained in:
Erica Fischer
2024-04-05 14:02:58 -07:00
parent 77f5e9677f
commit 3556142d80
2 changed files with 30 additions and 21 deletions
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projection.cpp
+15 -15
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@@ -107,22 +107,22 @@ void tiletoepsg3857(long long ix, long long iy, int zoom, double *ox, double *oy
// https://en.wikipedia.org/wiki/Hilbert_curve
void hilbert_rot(unsigned long long n, unsigned long long *x, unsigned long long *y, unsigned long long rx, unsigned long long ry) {
static void hilbert_rot(index_t n, unsigned long long *x, unsigned long long *y, index_t rx, index_t ry) {
if (ry == 0) {
if (rx == 1) {
*x = n - 1 - *x;
*y = n - 1 - *y;
}
unsigned t = *x;
unsigned long long t = *x;
*x = *y;
*y = t;
}
}
index_t hilbert_xy2d(unsigned long long n, unsigned long long x, unsigned long long y) {
static index_t hilbert_xy2d(index_t n, unsigned long long x, unsigned long long y) {
index_t d = 0;
unsigned long long rx, ry;
index_t rx, ry;
for (index_t s = n / 2; s > 0; s /= 2) {
rx = (x & s) != 0;
@@ -135,8 +135,8 @@ index_t hilbert_xy2d(unsigned long long n, unsigned long long x, unsigned long l
return d;
}
void hilbert_d2xy(index_t n, index_t d, unsigned long long *x, unsigned long long *y) {
unsigned long long rx, ry;
static void hilbert_d2xy(index_t n, index_t d, unsigned long long *x, unsigned long long *y) {
index_t rx, ry;
index_t t = d;
*x = *y = 0;
@@ -151,21 +151,21 @@ void hilbert_d2xy(index_t n, index_t d, unsigned long long *x, unsigned long lon
}
index_t encode_hilbert(unsigned long long wx, unsigned long long wy) {
return hilbert_xy2d(1LL << UINT_BITS, wx, wy);
return hilbert_xy2d((index_t) 1 << 64, wx, wy);
}
void decode_hilbert(index_t index, unsigned long long *wx, unsigned long long *wy) {
hilbert_d2xy(1LL << UINT_BITS, index, wx, wy);
hilbert_d2xy((index_t) 1 << 64, index, wx, wy);
}
index_t encode_quadkey(unsigned long long wx, unsigned long long wy) {
index_t out = 0;
int i;
for (i = 0; i < UINT_BITS; i++) {
index_t v = ((wx >> (UINT_BITS - (i + 1))) & 1) << 1;
v |= (wy >> (UINT_BITS - (i + 1))) & 1;
v = v << (64 - 2 * (i + 1));
for (i = 0; i < 64; i++) {
index_t v = ((wx >> (64 - (i + 1))) & 1) << 1;
v |= (wy >> (64 - (i + 1))) & 1;
v = v << (128 - 2 * (i + 1));
out |= v;
}
@@ -196,9 +196,9 @@ void decode_quadkey(index_t index, unsigned long long *wx, unsigned long long *w
*wx = *wy = 0;
for (size_t i = 0; i < 8; i++) {
*wx |= ((unsigned long long) decodex[(index >> (8 * i)) & 0xFF]) << (4 * i);
*wy |= ((unsigned long long) decodey[(index >> (8 * i)) & 0xFF]) << (4 * i);
for (size_t i = 0; i < 16; i++) {
*wx |= ((index_t) decodex[(index >> (8 * i)) & 0xFF]) << (4 * i);
*wy |= ((index_t) decodey[(index >> (8 * i)) & 0xFF]) << (4 * i);
}
}