Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Use in-place radix sort instead of quicksort #31

Closed
wants to merge 2 commits into from
Closed

Use in-place radix sort instead of quicksort #31

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
f266157
use in-place radix sort instead of quicksort
mourner Apr 1, 2020
56a7336
fixup partial radix sorting
mourner Apr 1, 2020
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
67 changes: 53 additions & 14 deletions index.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -133,7 +133,7 @@ export default class Flatbush {
}

// sort items by their Hilbert value (for packing later)
sort(hilbertValues, this._boxes, this._indices, 0, this.numItems - 1, this.nodeSize);
sort(hilbertValues, this._boxes, this._indices, 0, this.numItems, this.nodeSize, 24);

// generate nodes at each tree level, bottom-up
for (let i = 0, pos = 0; i < this._levelBounds.length - 1; i++) {
Expand Down Expand Up @@ -278,23 +278,62 @@ function upperBound(value, arr) {
return arr[i];
}

// custom quicksort that partially sorts bbox data alongside the hilbert values
function sort(values, boxes, indices, left, right, nodeSize) {
if (Math.floor(left / nodeSize) >= Math.floor(right / nodeSize)) return;
// custom radix sort that partially sorts bbox data alongside the hilbert values

const pivot = values[(left + right) >> 1];
let i = left - 1;
let j = right + 1;
const last = new Uint32Array(256);
const pointer0 = new Uint32Array(256);
const pointer8 = new Uint32Array(256);
const pointer16 = new Uint32Array(256);
const pointer24 = new Uint32Array(256);

while (true) {
do i++; while (values[i] < pivot);
do j--; while (values[j] > pivot);
if (i >= j) break;
swap(values, boxes, indices, i, j);
function sort(arr, boxes, indices, start, end, nodeSize, shift) {
const ptr =
shift === 0 ? pointer0 :
shift === 8 ? pointer8 :
shift === 16 ? pointer16 : pointer24;

for (let x = start; x < end; ++x) last[(arr[x] >> shift) & 0xFF]++;

last[0] += start;
ptr[0] = start;
for (let x = 1; x < 256; ++x) {
ptr[x] = last[x - 1];
last[x] += last[x - 1];
}

sort(values, boxes, indices, left, j, nodeSize);
sort(values, boxes, indices, j + 1, right, nodeSize);
for (let x = 0; x < 256; ++x) {
let i = ptr[x];
while (i !== last[x]) {
let value = arr[i], y;
while ((y = (value >> shift) & 0xFF) !== x) {
value = arr[ptr[y]];
swap(arr, boxes, indices, i, ptr[y]++);
}
i++;
}
ptr[x] = i;
last[x] = 0;
}

if (shift === 0) return;

for (let x = 0; x < 256; ++x) {
const i = x > 0 ? ptr[x - 1] : start;
const j = ptr[x];
if (Math.floor(i / nodeSize) < Math.floor((j - 1) / nodeSize)) {
if (j - i > 64) {
sort(arr, boxes, indices, i, j, nodeSize, shift - 8);
} else {
insertionSort(arr, boxes, indices, i, j);
}
}
}
}

function insertionSort(arr, boxes, indices, start, end) {
for (let x = start + 1; x < end; ++x) {
for (let y = x; y > start && arr[y - 1] > arr[y]; y--) swap(arr, boxes, indices, y, y - 1);
}
}

// swap two values and two corresponding boxes
Expand Down