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Allocate memory on stack whenever feasible

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The fast path gives another 20% speed up than the slower path.
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Chocobo1 2022-01-26 12:20:21 +08:00
parent 4e2daf117b
commit aafee60033
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1 changed files with 13 additions and 0 deletions
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13
src/base/bittorrent/ltqbitarray.cpp
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@ -47,9 +47,22 @@ namespace BitTorrent::LT
{ {
QBitArray toQBitArray(const lt::bitfield &bits) QBitArray toQBitArray(const lt::bitfield &bits)
{ {
const int STACK_ALLOC_SIZE = 10 * 1024;
const char *bitsData = bits.data(); const char *bitsData = bits.data();
const int dataLength = (bits.size() + 7) / 8; const int dataLength = (bits.size() + 7) / 8;
if (dataLength <= STACK_ALLOC_SIZE)
{
// fast path for small bitfields
char tmp[STACK_ALLOC_SIZE]; // uninitialized for faster allocation
for (int i = 0; i < dataLength; ++i)
tmp[i] = reverseByte(bitsData[i]);
return QBitArray::fromBits(tmp, bits.size());
}
// slow path for big bitfields
auto tmp = std::make_unique<char []>(dataLength); auto tmp = std::make_unique<char []>(dataLength);
for (int i = 0; i < dataLength; ++i) for (int i = 0; i < dataLength; ++i)
tmp[i] = reverseByte(bitsData[i]); tmp[i] = reverseByte(bitsData[i]);