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New, safer method of packing which makes careful use of casting to avoid problems with e.g. signed integer sign extension.

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David Williams
2015-03-21 08:48:45 +01:00
parent 905ec27f47
commit fd451be2dd
2 changed files with 44 additions and 6 deletions
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25
include/PolyVox/PagedVolume.h
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@ -285,17 +285,36 @@ namespace PolyVox
ChunkKey posToChunkKey(int32_t iXPos, int32_t iYPos, int32_t iZPos) const
{
int32_t iBlockX = iXPos >> m_uChunkSideLengthPower;
int32_t iBlockY = iYPos >> m_uChunkSideLengthPower;
int32_t iBlockZ = iZPos >> m_uChunkSideLengthPower;
int16_t iBlockXAsInt16 = static_cast<int16_t>(iBlockX);
int16_t iBlockYAsInt16 = static_cast<int16_t>(iBlockY);
int16_t iBlockZAsInt16 = static_cast<int16_t>(iBlockZ);
uint16_t uBlockXAsUint16 = reinterpret_cast<uint16_t&>(iBlockXAsInt16);
uint16_t uBlockYAsUint16 = reinterpret_cast<uint16_t&>(iBlockYAsInt16);
uint16_t uBlockZAsUint16 = reinterpret_cast<uint16_t&>(iBlockZAsInt16);
uint64_t uBlockXAsUint64 = static_cast<uint64_t>(uBlockXAsUint16);
uint64_t uBlockYAsUint64 = static_cast<uint64_t>(uBlockYAsUint16);
uint64_t uBlockZAsUint64 = static_cast<uint64_t>(uBlockZAsUint16);
uBlockXAsUint64 = uBlockXAsUint64 << 32;
uBlockYAsUint64 = uBlockYAsUint64 << 16;
// Bit-shifting of signed integer values has various issues with undefined or implementation-defined behaviour.
// Therefore we cast to unsigned to avoid these (we only care about the bit pattern anyway, not the actual value).
const ChunkKey uXPos = static_cast<ChunkKey>(iXPos);
/*const ChunkKey uXPos = static_cast<ChunkKey>(iXPos);
const ChunkKey uYPos = static_cast<ChunkKey>(iYPos);
const ChunkKey uZPos = static_cast<ChunkKey>(iZPos);
const ChunkKey xKey = ((uXPos >> m_uChunkSideLengthPower) & 0x3FF) << 20;
const ChunkKey yKey = ((uYPos >> m_uChunkSideLengthPower) & 0x3FF) << 10;
const ChunkKey zKey = ((uZPos >> m_uChunkSideLengthPower) & 0x3FF);
const ChunkKey zKey = ((uZPos >> m_uChunkSideLengthPower) & 0x3FF);*/
const ChunkKey key = 0x80000000 | xKey | yKey | zKey;
const ChunkKey key = 0xFFFF000000000000 | uBlockXAsUint64 | uBlockYAsUint64 | uBlockZAsUint64;
return key;
}