TerrainGen coverage

terraingen/
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noise/hash.h
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1 /// @file
2 /// @brief Stateless PCG hashes for the CPU and GPU backends (`portable.h`).
3 #pragma once
4
5 #include "terraingen/util/portable.h"
6
7 namespace terraingen {
8
9 /// Three 32-bit words.
10 struct UVec3 {
11 9 uint32_t x = 0; ///< First word.
12 8 uint32_t y = 0; ///< Second word.
13 7 uint32_t z = 0; ///< Third word.
14
15 #ifndef __SLANG__
16
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 9 bool operator==(const UVec3&) const = default;
17 #endif
18 };
19
20 /// PCG hash (PCG-RXS-M-XS over one LCG step) of one 32-bit word; bit-identical everywhere.
21 464330570 constexpr uint32_t PcgHash(uint32_t v) {
22 464330570 const uint32_t state = v * 747796405u + 2891336453u;
23 464330570 const uint32_t word = ((state >> ((state >> 28u) + 4u)) ^ state) * 277803737u;
24 464330570 return (word >> 22u) ^ word;
25 }
26
27 /// The `pcg3d` hash of three 32-bit words to three well-mixed words.
28 3976324006 constexpr UVec3 Pcg3dHash(UVec3 v) {
29 3976324006 v.x = v.x * 1664525u + 1013904223u;
30 3976324006 v.y = v.y * 1664525u + 1013904223u;
31 3976324006 v.z = v.z * 1664525u + 1013904223u;
32
33 3976324006 v.x += v.y * v.z;
34 3976324006 v.y += v.z * v.x;
35 3976324006 v.z += v.x * v.y;
36
37 3976324006 v.x ^= v.x >> 16u;
38 3976324006 v.y ^= v.y >> 16u;
39 3976324006 v.z ^= v.z >> 16u;
40
41 3976324006 v.x += v.y * v.z;
42 3976324006 v.y += v.z * v.x;
43 3976324006 v.z += v.x * v.y;
44 3976324006 return v;
45 }
46
47 /// Maps a hash to a float in [0, 1) from its top 24 bits, which a `float` represents exactly.
48 1583093841 constexpr float HashToUnitFloat(uint32_t hash) {
49 1583093841 return float(hash >> 8u) * 0x1p-24f;
50 }
51
52 } // namespace terraingen
53