Ely Office: six offline-first desktop apps in Rust and GPUI

ElyDoc, ElyTable, ElyShow (LibreOfficeKit), ElyPDF (MuPDF), ElyTree (Git),
ElyMark (Milkdown and CodeMirror in CEF). ElyMail and ElyAgent follow.

apps/ely-mark/web/src/diff.js

@@ -0,0 +1,53 @@
+// Myers' diff over two lists.
+
+/** Equal pairs between `a` and `b`, in order. */
+export function common(a, b, same) {
+  const n = a.length
+  const m = b.length
+  const max = n + m
+  const reach = new Map([[1, 0]])
+  const trace = []
+  for (let d = 0; d <= max; d++) {
+    trace.push(new Map(reach))
+    for (let k = -d; k <= d; k += 2) {
+      const down = k === -d || (k !== d && reach.get(k - 1) < reach.get(k + 1))
+      let x = down ? reach.get(k + 1) : reach.get(k - 1) + 1
+      let y = x - k
+      while (x < n && y < m && same(a[x], b[y])) {
+        x += 1
+        y += 1
+      }
+      reach.set(k, x)
+      if (x >= n && y >= m) return walk(trace, n, m)
+    }
+  }
+  throw new Error('diff did not end')
+}
+
+/** Back through the trace: each equal pair, in order. */
+function walk(trace, n, m) {
+  const pairs = []
+  let x = n
+  let y = m
+  for (let d = trace.length - 1; d > 0; d--) {
+    const reach = trace[d]
+    const k = x - y
+    const down = k === -d || (k !== d && reach.get(k - 1) < reach.get(k + 1))
+    const from = down ? k + 1 : k - 1
+    const fromX = reach.get(from)
+    const fromY = fromX - from
+    while (x > fromX + (down ? 0 : 1) && y > fromY + (down ? 1 : 0)) {
+      x -= 1
+      y -= 1
+      pairs.push([x, y])
+    }
+    x = fromX
+    y = fromY
+  }
+  while (x > 0 && y > 0) {
+    x -= 1
+    y -= 1
+    pairs.push([x, y])
+  }
+  return pairs.reverse()
+}