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Hilbert and quadkey 128-bit encodings are reversible

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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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unit.cpp
+15 -6
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@@ -124,20 +124,29 @@ TEST_CASE("Projection", "projection") {
}
TEST_CASE("Quadkey index", "quadkey index") {
unsigned x = (unsigned) 1234567890;
unsigned y = (unsigned) 3210987654;
unsigned long long a = (unsigned) 1234567890;
unsigned long long b = (unsigned) 3210987654;
unsigned long long x = (b << 32) | a;
unsigned long long y = (a << 32) | b;
index_t encoded;
unsigned long long nx, ny;
encoded = encode_quadkey(x, y);
REQUIRE((unsigned long long) encoded == 7338499239188161052);
// the *bottom* 64 bits of the 128-bit encoding
// are the same as the 64-bit encoding of a, b
REQUIRE((unsigned long long) encoded == 7338499239188161052ULL);
REQUIRE((unsigned long long) (encoded >> 64) == 11163131681630900524ULL);
decode_quadkey(encoded, &nx, &ny);
REQUIRE(nx == x);
REQUIRE(ny == y);
encoded = encode_hilbert(x, y);
REQUIRE((unsigned long long) encoded == 8447864191955811122);
decode_hilbert(encoded, &nx, &ny);
encoded = encode_hilbert(y, x);
// the *top* 64 bits of the 128-bit encoding
// of the 64-bit encoding of a, b
REQUIRE((unsigned long long) (encoded >> 64) == 8447864191955811122ULL);
REQUIRE((unsigned long long) encoded == 16122461378071376152ULL);
decode_hilbert(encoded, &ny, &nx);
REQUIRE(nx == x);
REQUIRE(ny == y);
}