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Minor micro-optimizations
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@chusitoo
chusitoo committed Jan 27, 2025
1 parent 8c895db commit 5ccafdf
Showing 1 changed file with 56 additions and 61 deletions.
117 changes: 56 additions & 61 deletions flatbush.h
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Original file line number Diff line number Diff line change
Expand Up @@ -95,62 +95,59 @@ To bit_cast(From const& from) {

// From https://github.com/rawrunprotected/hilbert_curves (public domain)
inline uint32_t Interleave(uint32_t x) {
x = (x | (x << 8)) & 0x00FF00FF;
x = (x | (x << 4)) & 0x0F0F0F0F;
x = (x | (x << 2)) & 0x33333333;
x = (x | (x << 1)) & 0x55555555;
x = (x | (x << 8U)) & 0x00FF00FF;
x = (x | (x << 4U)) & 0x0F0F0F0F;
x = (x | (x << 2U)) & 0x33333333;
x = (x | (x << 1U)) & 0x55555555;
return x;
}

inline uint32_t HilbertXYToIndex(uint32_t n, uint32_t x, uint32_t y) {
x = x << (16 - n);
y = y << (16 - n);

inline uint32_t HilbertXYToIndex(uint32_t x, uint32_t y) {
// Initial prefix scan round, prime with x and y
uint32_t a = x ^ y;
uint32_t b = 0xFFFF ^ a;
uint32_t c = 0xFFFF ^ (x | y);
uint32_t d = x & (y ^ 0xFFFF);
uint32_t A = a | (b >> 1);
uint32_t B = (a >> 1) ^ a;
uint32_t C = ((c >> 1) ^ (b & (d >> 1))) ^ c;
uint32_t D = ((a & (c >> 1)) ^ (d >> 1)) ^ d;
uint32_t A = a | (b >> 1U);
uint32_t B = (a >> 1U) ^ a;
uint32_t C = ((c >> 1U) ^ (b & (d >> 1U))) ^ c;
uint32_t D = ((a & (c >> 1U)) ^ (d >> 1U)) ^ d;

a = A;
b = B;
c = C;
d = D;
A = ((a & (a >> 2)) ^ (b & (b >> 2)));
B = ((a & (b >> 2)) ^ (b & ((a ^ b) >> 2)));
C ^= ((a & (c >> 2)) ^ (b & (d >> 2)));
D ^= ((b & (c >> 2)) ^ ((a ^ b) & (d >> 2)));
A = ((a & (a >> 2U)) ^ (b & (b >> 2U)));
B = ((a & (b >> 2U)) ^ (b & ((a ^ b) >> 2U)));
C ^= ((a & (c >> 2U)) ^ (b & (d >> 2U)));
D ^= ((b & (c >> 2U)) ^ ((a ^ b) & (d >> 2U)));

a = A;
b = B;
c = C;
d = D;
A = ((a & (a >> 4)) ^ (b & (b >> 4)));
B = ((a & (b >> 4)) ^ (b & ((a ^ b) >> 4)));
C ^= ((a & (c >> 4)) ^ (b & (d >> 4)));
D ^= ((b & (c >> 4)) ^ ((a ^ b) & (d >> 4)));
A = ((a & (a >> 4U)) ^ (b & (b >> 4U)));
B = ((a & (b >> 4U)) ^ (b & ((a ^ b) >> 4U)));
C ^= ((a & (c >> 4U)) ^ (b & (d >> 4U)));
D ^= ((b & (c >> 4U)) ^ ((a ^ b) & (d >> 4U)));

// Final round and projection
a = A;
b = B;
c = C;
d = D;
C ^= ((a & (c >> 8)) ^ (b & (d >> 8)));
D ^= ((b & (c >> 8)) ^ ((a ^ b) & (d >> 8)));
C ^= ((a & (c >> 8U)) ^ (b & (d >> 8U)));
D ^= ((b & (c >> 8U)) ^ ((a ^ b) & (d >> 8U)));

// Undo transformation prefix scan
a = C ^ (C >> 1);
b = D ^ (D >> 1);
a = C ^ (C >> 1U);
b = D ^ (D >> 1U);

// Recover index bits
uint32_t i0 = x ^ y;
uint32_t i1 = b | (0xFFFF ^ (i0 | a));

return ((Interleave(i1) << 1U) | Interleave(i0)) >> (32 - 2 * n);
return ((Interleave(i1) << 1U) | Interleave(i0));
}

// Template specialization for the supported array types
Expand Down Expand Up @@ -267,7 +264,7 @@ class FlatbushBuilder {

inline size_t add(const Box<ArrayType>& iBox) noexcept {
mItems.push_back(iBox);
return mItems.size() - 1;
return mItems.size() - 1UL;
}

Flatbush<ArrayType> finish() const;
Expand Down Expand Up @@ -319,7 +316,7 @@ Flatbush<ArrayType> FlatbushBuilder<ArrayType>::from(const uint8_t* iData, size_
" data when expected v" + std::to_string(gVersion) + ".");
}

const auto wExpectedType = detail::arrayTypeIndex<ArrayType>();
constexpr auto wExpectedType = detail::arrayTypeIndex<ArrayType>();
const uint8_t wEncodedType = iData[1] & 0x0fU;
if (wExpectedType != wEncodedType) {
throw std::invalid_argument("Expected type is " + detail::arrayTypeName(wEncodedType) +
Expand Down Expand Up @@ -400,7 +397,7 @@ class Flatbush {
#else
const auto wIsNanPoint = (std::isnan(iPoint.mX) || std::isnan(iPoint.mY));
#endif
return !wIsNanPoint && !std::isnan(iMaxDistance) && iMaxDistance >= 0 && iMaxResults != 0;
return !wIsNanPoint && !std::isnan(iMaxDistance) && iMaxDistance >= 0.0 && iMaxResults != 0UL;
}

explicit Flatbush(uint32_t iNumItems, uint16_t iNodeSize) noexcept;
Expand All @@ -414,7 +411,7 @@ class Flatbush {
size_t upperBound(size_t iNodeIndex) const noexcept;

struct IndexDistance {
IndexDistance(size_t iId, ArrayType iDistance) : mId(iId), mDistance(iDistance) {}
IndexDistance(size_t iId, ArrayType iDistance) noexcept : mId(iId), mDistance(iDistance) {}
bool operator<(const IndexDistance& iOther) const { return iOther.mDistance < mDistance; }
bool operator>(const IndexDistance& iOther) const { return iOther.mDistance > mDistance; }

Expand All @@ -440,7 +437,7 @@ Flatbush<ArrayType>::Flatbush(uint32_t iNumItems, uint16_t iNodeSize) noexcept {
iNodeSize = std::min(std::max(iNodeSize, gMinNodeSize), gMaxNodeSize);
init(iNumItems, iNodeSize);

mData.assign(mData.capacity(), 0);
mData.assign(mData.capacity(), 0U);
mData[0] = gValidityFlag;
mData[1] = (gVersion << 4U) + detail::arrayTypeIndex<ArrayType>();
*detail::bit_cast<uint16_t*>(&mData[2]) = iNodeSize;
Expand All @@ -454,9 +451,9 @@ Flatbush<ArrayType>::Flatbush(const uint8_t* iData, size_t iSize) noexcept {
init(wNumItems, wNodeSize);

mData.insert(mData.begin(), iData, iData + iSize);
mPosition = mLevelBounds.empty() ? 0 : mLevelBounds.back();
if (mPosition > 0) {
mBounds = mBoxes[mPosition - 1];
mPosition = mLevelBounds.empty() ? 0UL : mLevelBounds.back();
if (mPosition > 0UL) {
mBounds = mBoxes[mPosition - 1UL];
}
}

Expand All @@ -471,10 +468,10 @@ void Flatbush<ArrayType>::init(uint32_t iNumItems, uint32_t iNodeSize) noexcept
mLevelBounds.push_back(wNumNodes);

do {
wCount = (wCount + iNodeSize - 1) / iNodeSize;
wCount = (wCount + iNodeSize - 1UL) / iNodeSize;
wNumNodes += wCount;
mLevelBounds.push_back(wNumNodes);
} while (wCount > 1);
} while (wCount > 1UL);

// Sizes
mIsWideIndex = wNumNodes > gMaxNumNodes;
Expand Down Expand Up @@ -521,17 +518,16 @@ void Flatbush<ArrayType>::finish() noexcept {
const auto wHilbertHeight = gMaxHilbert / (mBounds.mMaxY - mBounds.mMinY);

// map item centers into Hilbert coordinate space and calculate Hilbert values
for (size_t wIdx = 0; wIdx < wNumItems; ++wIdx) {
wHilbertValues[wIdx] = detail::HilbertXYToIndex(
16,
for (size_t wIdx = 0UL; wIdx < wNumItems; ++wIdx) {
wHilbertValues.at(wIdx) = detail::HilbertXYToIndex(
uint32_t(wHilbertWidth * ((mBoxes[wIdx].mMinX + mBoxes[wIdx].mMaxX) / 2 - mBounds.mMinX)),
uint32_t(wHilbertHeight * ((mBoxes[wIdx].mMinY + mBoxes[wIdx].mMaxY) / 2 - mBounds.mMinY)));
}

// sort items by their Hilbert value (for packing later)
sort(wHilbertValues, 0, wNumItems - 1);
sort(wHilbertValues, 0U, wNumItems - 1U);

for (size_t wIdx = 0, wPosition = 0; wIdx < mLevelBounds.size() - 1; ++wIdx) {
for (size_t wIdx = 0UL, wPosition = 0UL; wIdx < mLevelBounds.size() - 1UL; ++wIdx) {
const auto wEnd = mLevelBounds[wIdx];

// generate a parent node for each block of consecutive <nodeSize> nodes
Expand Down Expand Up @@ -565,18 +561,18 @@ void Flatbush<ArrayType>::sort(std::vector<uint32_t>& iValues,
size_t iLeft,
size_t iRight) noexcept {
if (iLeft < iRight) {
const auto wPivot = iValues[(iLeft + iRight) >> 1];
auto wPivotLeft = iLeft - 1;
auto wPivotRight = iRight + 1;
const auto wPivot = iValues.at((iLeft + iRight) >> 1U);
auto wPivotLeft = iLeft - 1U;
auto wPivotRight = iRight + 1U;

while (true) {
do {
++wPivotLeft;
} while (iValues[wPivotLeft] < wPivot);
} while (iValues.at(wPivotLeft) < wPivot);

do {
--wPivotRight;
} while (iValues[wPivotRight] > wPivot);
} while (iValues.at(wPivotRight) > wPivot);

if (wPivotLeft >= wPivotRight) {
break;
Expand All @@ -586,7 +582,7 @@ void Flatbush<ArrayType>::sort(std::vector<uint32_t>& iValues,
}

sort(iValues, iLeft, wPivotRight);
sort(iValues, wPivotRight + 1, iRight);
sort(iValues, wPivotRight + 1U, iRight);
}
}

Expand All @@ -595,7 +591,7 @@ template <typename ArrayType>
void Flatbush<ArrayType>::swap(std::vector<uint32_t>& iValues,
size_t iLeft,
size_t iRight) noexcept {
std::swap(iValues[iLeft], iValues[iRight]);
std::swap(iValues.at(iLeft), iValues.at(iRight));
std::swap(mBoxes[iLeft], mBoxes[iRight]);

if (mIsWideIndex) {
Expand All @@ -617,7 +613,7 @@ std::vector<size_t> Flatbush<ArrayType>::search(const Box<ArrayType>& iBounds,
const auto wCanLoop = canDoSearch(iBounds);
const auto wNumItems = numItems();
const auto wNodeSize = nodeSize();
auto wNodeIndex = mBoxes.size() - 1;
auto wNodeIndex = mBoxes.size() - 1UL;
std::queue<size_t> wQueue;
std::vector<size_t> wResults;

Expand All @@ -634,7 +630,8 @@ std::vector<size_t> Flatbush<ArrayType>::search(const Box<ArrayType>& iBounds,
iBounds.mMinY > mBoxes[wPosition].mMaxY /* minY > nodeMaxY */) {
continue;
}
const size_t wIndex = (mIsWideIndex ? mIndicesUint32[wPosition] : mIndicesUint16[wPosition]);

const size_t wIndex = mIsWideIndex ? mIndicesUint32[wPosition] : mIndicesUint16[wPosition];

if (wNodeIndex >= wNumItems) {
wQueue.push(wIndex); // node; add it to the search queue
Expand All @@ -646,7 +643,8 @@ std::vector<size_t> Flatbush<ArrayType>::search(const Box<ArrayType>& iBounds,
if (wQueue.empty()) {
break;
}
wNodeIndex = wQueue.front() >> 2; // for binary compatibility with JS

wNodeIndex = wQueue.front() >> 2U; // for binary compatibility with JS
wQueue.pop();
}

Expand All @@ -662,7 +660,7 @@ std::vector<size_t> Flatbush<ArrayType>::neighbors(const Point<ArrayType>& iPoin
const auto wMaxDistSquared = iMaxDistance * iMaxDistance;
const auto wNumItems = numItems();
const auto wNodeSize = nodeSize();
auto wNodeIndex = mBoxes.size() - 1;
auto wNodeIndex = mBoxes.size() - 1UL;
std::priority_queue<IndexDistance> wQueue;
std::vector<size_t> wResults;

Expand All @@ -676,24 +674,20 @@ std::vector<size_t> Flatbush<ArrayType>::neighbors(const Point<ArrayType>& iPoin
const auto wDistX = axisDistance(iPoint.mX, mBoxes[wPosition].mMinX, mBoxes[wPosition].mMaxX);
const auto wDistY = axisDistance(iPoint.mY, mBoxes[wPosition].mMinY, mBoxes[wPosition].mMaxY);
const auto wDistance = wDistX * wDistX + wDistY * wDistY;

if (wDistance > wMaxDistSquared) {
continue;
}

if (wNodeIndex >= wNumItems) {
} else if (wNodeIndex >= wNumItems) {
wQueue.emplace(wIndex << 1U, wDistance);
} else if (!iFilterFn || iFilterFn(wIndex)) {
// put an odd index if it's an item rather than a node, to recognize later
wQueue.emplace((wIndex << 1U) + 1, wDistance); // leaf node
wQueue.emplace((wIndex << 1U) + 1U, wDistance); // leaf node
}
}

// pop items from the queue
while (!wQueue.empty() && (wQueue.top().mId & 1)) {
if (wQueue.top().mDistance > wMaxDistSquared) {
return wResults;
}
wResults.push_back(wQueue.top().mId >> 1);
while (!wQueue.empty() && (wQueue.top().mId & 1U)) {
wResults.push_back(wQueue.top().mId >> 1U);
wQueue.pop();
if (wResults.size() >= iMaxResults) {
return wResults;
Expand All @@ -703,7 +697,8 @@ std::vector<size_t> Flatbush<ArrayType>::neighbors(const Point<ArrayType>& iPoin
if (wQueue.empty()) {
break;
}
wNodeIndex = wQueue.top().mId >> 3; // 1 to undo indexing + 2 for binary compatibility with JS

wNodeIndex = wQueue.top().mId >> 3U; // 1 to undo indexing + 2 for binary compatibility with JS
wQueue.pop();
}

Expand Down

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