From fea8b61daed97ede1cbce928e3a9af4c1d033953 Mon Sep 17 00:00:00 2001
From: Peter Bower <37089506+pbower@users.noreply.github.com>
Date: Fri, 2 Oct 2026 04:08:52 +0100
Subject: [PATCH 1/3] Write scatter_indices bits without per-element capacity
 checks

---
 src/enums/array.rs | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/enums/array.rs b/src/enums/array.rs
index 8b9b7f1..8e18196 100644
--- a/src/enums/array.rs
+++ b/src/enums/array.rs
@@ -1507,14 +1507,24 @@ impl Array {
                 match $src_mask {
                     Some(sm) => {
                         let mask = $dst_mask.get_or_insert_with(|| Bitmask::new_set_all(dst_len, true));
+                        mask.ensure_capacity(dst_len);
                         for (&d, &s) in dst_idx.iter().zip(src_idx) {
-                            mask.set(d, sm.get(offset + s));
+                            // Safety: the bounds checks above put every `d`
+                            // inside this array and every `s` inside the
+                            // window, `ensure_capacity` sizes this mask to the
+                            // array, and the source mask spans its backing
+                            // array.
+                            unsafe { mask.set_unchecked(d, sm.get_unchecked(offset + s)) };
                         }
                     }
                     None => {
                         if let Some(mask) = $dst_mask.as_mut() {
+                            mask.ensure_capacity(dst_len);
                             for &d in dst_idx {
-                                mask.set(d, true);
+                                // Safety: the bounds check above puts every
+                                // `d` inside this array, and `ensure_capacity`
+                                // sizes this mask to the array.
+                                unsafe { mask.set_unchecked(d, true) };
                             }
                         }
                     }
@@ -1645,8 +1655,12 @@ impl Array {
             },
             (Array::BooleanArray(d), Array::BooleanArray(s)) => {
                 let dst = Arc::make_mut(d);
+                dst.data.ensure_capacity(dst_len);
                 for (&di, &si) in dst_idx.iter().zip(src_idx) {
-                    dst.data.set(di, s.data.get(offset + si));
+                    // Safety: the bounds checks above put every `di` inside
+                    // this array and every `si` inside the window, and
+                    // `ensure_capacity` sizes the value bits to the array.
+                    unsafe { dst.data.set_unchecked(di, s.data.get_unchecked(offset + si)) };
                 }
                 scatter_mask!(dst.null_mask, s.null_mask.as_ref());
             }

From d24311b42a916f3d03c7fe2d5d8db33241d63fd7 Mon Sep 17 00:00:00 2001
From: Peter Bower <37089506+pbower@users.noreply.github.com>
Date: Fri, 2 Oct 2026 04:30:07 +0100
Subject: [PATCH 2/3] Update array.rs

---
 src/enums/array.rs | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/enums/array.rs b/src/enums/array.rs
index 8e18196..34ea968 100644
--- a/src/enums/array.rs
+++ b/src/enums/array.rs
@@ -1509,11 +1509,11 @@ impl Array {
                         let mask = $dst_mask.get_or_insert_with(|| Bitmask::new_set_all(dst_len, true));
                         mask.ensure_capacity(dst_len);
                         for (&d, &s) in dst_idx.iter().zip(src_idx) {
-                            // Safety: the bounds checks above put every `d`
-                            // inside this array and every `s` inside the
-                            // window, `ensure_capacity` sizes this mask to the
-                            // array, and the source mask spans its backing
-                            // array.
+                            // Safety: 
+                            // - the bounds checks above ensures every `d`
+                            // is inside this array and every `s` inside the window
+                            // - `ensure_capacity` sizes this mask to the array
+                            // - the source mask spans its backing array.
                             unsafe { mask.set_unchecked(d, sm.get_unchecked(offset + s)) };
                         }
                     }
@@ -1521,9 +1521,9 @@ impl Array {
                         if let Some(mask) = $dst_mask.as_mut() {
                             mask.ensure_capacity(dst_len);
                             for &d in dst_idx {
-                                // Safety: the bounds check above puts every
-                                // `d` inside this array, and `ensure_capacity`
-                                // sizes this mask to the array.
+                                // Safety: 
+                                // - the bounds check above ensures every `d` is inside this array
+                                // - `ensure_capacity` sizes this mask to the array.
                                 unsafe { mask.set_unchecked(d, true) };
                             }
                         }

From a0adcbf039bf5bc4be265d14d3b3d341827d6d8e Mon Sep 17 00:00:00 2001
From: Peter Bower <37089506+pbower@users.noreply.github.com>
Date: Fri, 2 Oct 2026 04:31:48 +0100
Subject: [PATCH 3/3] Update array.rs

---
 src/enums/array.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/enums/array.rs b/src/enums/array.rs
index 34ea968..5fac2e3 100644
--- a/src/enums/array.rs
+++ b/src/enums/array.rs
@@ -1657,9 +1657,10 @@ impl Array {
                 let dst = Arc::make_mut(d);
                 dst.data.ensure_capacity(dst_len);
                 for (&di, &si) in dst_idx.iter().zip(src_idx) {
-                    // Safety: the bounds checks above put every `di` inside
-                    // this array and every `si` inside the window, and
-                    // `ensure_capacity` sizes the value bits to the array.
+                    // Safety: 
+                    // - the bounds checks above mean every `di` is inside
+                    // this array and every `si` inside the window
+                    // - `ensure_capacity` sizes the value bits to the array.
                     unsafe { dst.data.set_unchecked(di, s.data.get_unchecked(offset + si)) };
                 }
                 scatter_mask!(dst.null_mask, s.null_mask.as_ref());