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Simplify and optimize Hilbert tile ID <-> XYZ conversion (#527)

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* Optimize Hilbert tile ID <-> XYZ conversion

* biome

* tile_id: more improvements

* tile_id(cpp): uint32
This commit is contained in:
Taku Fukada
2025-02-21 16:37:49 +09:00
committed by GitHub
parent caa8f1f726
commit 9b69ab4b64
4 changed files with 122 additions and 157 deletions
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74
cpp/pmtiles.hpp
View File

@@ -321,35 +321,18 @@ uint64_t decode_varint(const char **data, const char *end) {
return decode_varint_impl(data, end);
}
void rotate(int64_t n, int64_t &x, int64_t &y, int64_t rx, int64_t ry) {
void rotate(int64_t n, uint32_t &x, uint32_t &y, uint32_t rx, uint32_t ry) {
if (ry == 0) {
if (rx == 1) {
if (rx != 0) {
x = n - 1 - x;
y = n - 1 - y;
}
int64_t t = x;
uint32_t t = x;
x = y;
y = t;
}
}
zxy t_on_level(uint8_t z, uint64_t pos) {
int64_t n = 1LL << z;
int64_t rx, ry, s, t = pos;
int64_t tx = 0;
int64_t ty = 0;
for (s = 1; s < n; s *= 2) {
rx = 1LL & (t / 2);
ry = 1LL & (t ^ rx);
rotate(s, tx, ty, rx, ry);
tx += s * rx;
ty += s * ry;
t /= 4;
}
return zxy(z, static_cast<int>(tx), static_cast<int>(ty));
}
int write_varint(std::back_insert_iterator<std::string> data, uint64_t value) {
int n = 1;
@@ -405,16 +388,31 @@ entryv3 find_tile(const std::vector<entryv3> &entries, uint64_t tile_id) {
} // end anonymous namespace
// Note: std::bit_width is available in C++20 and later.
static uint8_t bit_width(uint64_t n) {
uint8_t count = 0;
while (n > 0) { count++; n >>= 1; }
return count;
}
inline zxy tileid_to_zxy(uint64_t tileid) {
uint64_t acc = 0;
for (uint8_t t_z = 0; t_z < 32; t_z++) {
uint64_t num_tiles = (1LL << t_z) * (1LL << t_z);
if (acc + num_tiles > tileid) {
return t_on_level(t_z, tileid - acc);
}
acc += num_tiles;
if (tileid > 6148914691236517204) {
throw std::overflow_error("tile zoom exceeds 64-bit limit");
}
throw std::overflow_error("tile zoom exceeds 64-bit limit");
uint8_t z = (bit_width(3 * tileid + 1) - 1) / 2;
uint64_t acc = ((1L << (z * 2)) - 1) / 3;
uint64_t pos = tileid - acc;
uint32_t x = 0, y = 0;
for (uint8_t a = 0; a < z; a++) {
uint64_t s = 1 << a;
uint32_t rx = s & (pos / 2);
uint32_t ry = s & (pos ^ rx);
rotate(s, x, y, rx, ry);
pos >>= 1;
x += rx;
y += ry;
}
return zxy(z, static_cast<int>(x), static_cast<int>(y));
}
inline uint64_t zxy_to_tileid(uint8_t z, uint32_t x, uint32_t y) {
@@ -424,19 +422,17 @@ inline uint64_t zxy_to_tileid(uint8_t z, uint32_t x, uint32_t y) {
if (x > (1U << z) - 1U || y > (1U << z) - 1U) {
throw std::overflow_error("tile x/y outside zoom level bounds");
}
uint64_t acc = 0;
for (uint8_t t_z = 0; t_z < z; t_z++) acc += (1LL << t_z) * (1LL << t_z);
int64_t n = 1LL << z;
int64_t rx, ry, s, d = 0;
int64_t tx = x;
int64_t ty = y;
for (s = n / 2; s > 0; s /= 2) {
rx = (tx & s) > 0;
ry = (ty & s) > 0;
d += s * s * ((3LL * rx) ^ ry);
uint64_t acc = ((1LL << (z * 2U)) - 1) / 3;
uint32_t tx = x, ty = y;
int a = z - 1;
for (uint32_t s = 1LL << a; s > 0; s >>= 1) {
uint32_t rx = s & tx;
uint32_t ry = s & ty;
rotate(s, tx, ty, rx, ry);
acc += ((3LL * rx) ^ ry) << a;
a--;
}
return acc + d;
return acc;
}
// returns an uncompressed byte buffer

3
cpp/test.cpp
View File

@@ -72,7 +72,6 @@ MU_TEST(test_roundtrip) {
} catch (const std::runtime_error &e) {
caught = true;
}
mu_check(caught);
caught = false;
@@ -81,7 +80,6 @@ MU_TEST(test_roundtrip) {
} catch (const std::runtime_error &e) {
caught = true;
}
mu_check(caught);
caught = false;
@@ -90,7 +88,6 @@ MU_TEST(test_roundtrip) {
} catch (const std::runtime_error &e) {
caught = true;
}
mu_check(caught);
caught = false;