ocrm.bsky.social
the game where you go into mines and start crafting! but for consoles (forked directly from smartcmd's github)
1#pragma once
2
3// 4J added - Storage for data (ie the extra per tile storage). Data is normally stored as 4-bits per tile, in a DataLayer class of 16384 bytes ( 128 x 16 x 16 x 0.5 )
4// This class provides more economical storage for such data by taking into consideration that it is quite common for large parts of the data to be very compressible (ie zero).
5// We are aiming here to balance performance (this data is accessed very frequently) against size.
6
7// Details of storage method:
8
9// 1. Data is split into horizontal planes, of which there are 128, and each taking up 128 bytes (16 x 16 x 0.5)
10// 2. Each of these layers has a permanently allocated index in this class (planeIndices).
11// 3. Data for allocatedPlaneCount planes worth of data is allocated in the data array ( allocatedPlaneCount * 128 bytes )
12// 4. If a plane index for a layer is < 128, then the data for that layer is at data[ index * 128 ]
13// 5. If a plane index for a layer is 128, then all values for that plane are 0
14
15// This class needs to be thread safe as there are times where chunk data is shared between server & main threads. Data values are queried
16// very regularly so this needs to be as light-weight as possible.
17
18// To meet these requirements, this class is now implemented using a lock-free system, implemented using a read-copy-update (RCU) type algorithm. Some details...
19
20// (1) The storage details for the class are now packed into a single __int64, which contains both a pointer to the data that is required and a count of how many planes worth
21// of storage are allocated. This allows the full storage to be updated atomically using compare and exchange operations (implemented with InterlockedCompareExchangeRelease64).
22// (2) The data pointer referenced in this __int64 points to an area of memory which is 128 + 128 * plane_count bytes long, where the first 128 bytes stoere the plane indices, and
23// the rest of the data is variable in size to accomodate however many planes are required to be stored
24// (3) The RCU bit of the algorithm means that any read operations don't need to do any checks or locks at all. When the data needs to be updated, a copy of it is made and updated,
25// then an attempt is made to swap the new data in - if this succeeds then the old data pointer is deleted later at some point where we know nothing will be reading from it anymore.
26// This is achieved by putting the delete request in a queue which means it won't actually get deleted until 2 game ticks after the last time its reference existed, which should give
27// us a large margin of safety. If the attempt to swap the new data in fails, then the whole write operation has to be attempted again - this is the only time there is really a
28// high cost for this algorithm and such write collisions should be rare.
29
30//#define DATA_COMPRESSION_STATS
31
32class SparseDataStorage_SPU
33{
34private:
35// unsigned char planeIndices[128];
36 unsigned char* m_pData;
37
38// unsigned char *data;
39// unsigned int allocatedPlaneCount;
40
41 static const int ALL_0_INDEX = 128;
42
43public:
44 SparseDataStorage_SPU(unsigned char* data) : m_pData(data) {}
45
46 unsigned char* getDataPtr() { return m_pData; }
47
48 int get(int x, int y, int z) // Get an individual data value
49 {
50 unsigned char *planeIndices, *data;
51 getPlaneIndicesAndData(&planeIndices, &data);
52
53 if( planeIndices[y] == ALL_0_INDEX )
54 {
55 return 0;
56 }
57 else
58 {
59 int planeIndex = x * 16 + z; // Index within this xz plane
60 int byteIndex = planeIndex / 2; // Byte index within the plane (2 tiles stored per byte)
61 int shift = ( planeIndex & 1 ) * 4; // Bit shift within the byte
62 int retval = ( data[ planeIndices[y] * 128 + byteIndex ] >> shift ) & 15;
63
64 return retval;
65 }
66 }
67
68 void getPlaneIndicesAndData(unsigned char **planeIndices, unsigned char **data)
69 {
70 *planeIndices = m_pData;
71 *data = m_pData + 128;
72 }
73
74};
75