Fix descriptor.Table buffer growth calc

internal/descriptor/table.go

@@ -37,23 +37,19 @@ func (t *Table[Key, Item]) Len() (n int) {
 	return n
 }
 
-// grow ensures that t has enough room for n items, potentially reallocating the
-// internal buffers if their capacity was too small to hold this many items.
+// grow grows the table by n * 64 items.
 func (t *Table[Key, Item]) grow(n int) {
-	// Round up to a multiple of 64 since this is the smallest increment due to
-	// using 64 bits masks.
-	n = (n*64 + 63) / 64
-
-	if n > len(t.masks) {
-		masks := make([]uint64, n)
-		copy(masks, t.masks)
-
-		items := make([]Item, n*64)
-		copy(items, t.items)
+	total := len(t.masks) + n
+	if total > cap(t.masks) {
+		t.masks = append(t.masks, make([]uint64, n)...)
+	}
+	t.masks = t.masks[:total]
 
-		t.masks = masks
-		t.items = items
+	total = len(t.items) + n*64
+	if total > cap(t.items) {
+		t.items = append(t.items, make([]Item, n*64)...)
 	}
+	t.items = t.items[:total]
 }
 
 // Insert inserts the given item to the table, returning the key that it is
@@ -78,13 +74,9 @@ insert:
 		}
 	}
 
+	// No free slot found, grow the table and retry.
 	offset = len(t.masks)
-	n := 2 * len(t.masks)
-	if n == 0 {
-		n = 1
-	}
-
-	t.grow(n)
+	t.grow(1)
 	goto insert
 }
 
@@ -109,10 +101,10 @@ func (t *Table[Key, Item]) InsertAt(item Item, key Key) bool {
 	if key < 0 {
 		return false
 	}
-	if diff := int(key) - t.Len(); diff > 0 {
+	index := uint(key) / 64
+	if diff := int(index) - len(t.masks) + 1; diff > 0 {
 		t.grow(diff)
 	}
-	index := uint(key) / 64
 	shift := uint(key) % 64
 	t.masks[index] |= 1 << shift
 	t.items[key] = item
@@ -124,7 +116,8 @@ func (t *Table[Key, Item]) Delete(key Key) {
 	if key < 0 { // invalid key
 		return
 	}
-	if index, shift := key/64, key%64; int(index) < len(t.masks) {
+	if index := uint(key) / 64; int(index) < len(t.masks) {
+		shift := uint(key) % 64
 		mask := t.masks[index]
 		if (mask & (1 << shift)) != 0 {
 			var zero Item