From e7d0d152fc3e508d649a31cb04f25a847d4d88fe Mon Sep 17 00:00:00 2001
From: cynecx <me@cynecx.net>
Date: Sun, 4 Feb 2024 20:16:53 +0100
Subject: [PATCH 1/2] Replace modulo ops with bitwise-and equivalent

---
 src/lib.rs | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 4ccc6f0..e78b1c9 100755
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -420,6 +420,13 @@ pub(crate) fn round_down_to(n: usize, divisor: usize) -> usize {
     n & !(divisor - 1)
 }
 
+#[inline]
+pub(crate) fn round_mut_ptr_down_to(ptr: *mut u8, divisor: usize) -> *mut u8 {
+    debug_assert!(divisor > 0);
+    debug_assert!(divisor.is_power_of_two());
+    ptr.wrapping_sub(ptr as usize & (divisor - 1))
+}
+
 // After this point, we try to hit page boundaries instead of powers of 2
 const PAGE_STRATEGY_CUTOFF: usize = 0x1000;
 
@@ -1412,8 +1419,7 @@ impl Bump {
             }
 
             let ptr = ptr.wrapping_sub(layout.size());
-            let rem = ptr as usize % layout.align();
-            let aligned_ptr = ptr.wrapping_sub(rem);
+            let aligned_ptr = round_mut_ptr_down_to(ptr, layout.align());
 
             if aligned_ptr >= start {
                 let aligned_ptr = NonNull::new_unchecked(aligned_ptr);
@@ -1508,7 +1514,7 @@ impl Bump {
             // at least the requested size.
             let mut ptr = new_footer.ptr.get().as_ptr().sub(size);
             // Round the pointer down to the requested alignment.
-            ptr = ptr.sub(ptr as usize % layout.align());
+            ptr = round_mut_ptr_down_to(ptr, layout.align());
             debug_assert!(
                 ptr as *const _ <= new_footer,
                 "{:p} <= {:p}",

From 6022968c95d5c84fdbb7ecff7ecbc0346d46e60c Mon Sep 17 00:00:00 2001
From: Nick Fitzgerald <fitzgen@gmail.com>
Date: Fri, 9 Feb 2024 08:32:34 -0800
Subject: [PATCH 2/2] Add doc comment for helper function

---
 src/lib.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/lib.rs b/src/lib.rs
index e78b1c9..600f6ad 100755
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -420,6 +420,7 @@ pub(crate) fn round_down_to(n: usize, divisor: usize) -> usize {
     n & !(divisor - 1)
 }
 
+/// Same as `round_down_to` but preserves pointer provenance.
 #[inline]
 pub(crate) fn round_mut_ptr_down_to(ptr: *mut u8, divisor: usize) -> *mut u8 {
     debug_assert!(divisor > 0);