From 1ba421505037fe8c53a8f13967abf96a7e5f02ec Mon Sep 17 00:00:00 2001
From: Lokathor <zefria@gmail.com>
Date: Tue, 5 Sep 2023 14:08:36 -0600
Subject: [PATCH] Create `align_offset` feature so that we can continue to work
 on 1.34

---
 Cargo.toml      | 15 +++++++++++----
 src/internal.rs | 17 ++++++++++++-----
 2 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 0a82e8b..e6d77a0 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -18,12 +18,19 @@ extern_crate_alloc = []
 extern_crate_std = ["extern_crate_alloc"]
 zeroable_maybe_uninit = []
 zeroable_atomics = []
-min_const_generics = []
-wasm_simd = [] # Until >= 1.54.0 is MSRV this is an off-by-default feature.
-must_cast = [] # Until >= 1.57.0 is MSRV this is an off-by-default feature.
+
+# Causes MSRV 1.36, use `align_offset` method instead of casting to `usize` to
+# check alignment of pointers, this *may* improve codegen in some cases (but it
+# has never been formally benchmarked!)
+align_offset = []
+
+min_const_generics = [] # Causes MSRV 1.51
+
+wasm_simd = []    # Until >= 1.54.0 is MSRV this is an off-by-default feature.
+must_cast = []    # Until >= 1.57.0 is MSRV this is an off-by-default feature.
 aarch64_simd = [] # Until >= 1.59.0 is MSRV this is an off-by-default feature.
 
-# Do not use if you can avoid it, because this is unsound.
+# Do not use if you can avoid it, because this is **unsound**!!!!
 unsound_ptr_pod_impl = []
 
 # NOT SEMVER SUPPORTED! TEMPORARY ONLY!
diff --git a/src/internal.rs b/src/internal.rs
index be8c309..3ede50f 100644
--- a/src/internal.rs
+++ b/src/internal.rs
@@ -136,11 +136,18 @@ pub(crate) unsafe fn pod_read_unaligned<T: Copy>(bytes: &[u8]) -> T {
 /// * If `align` is not a power of two. This includes when `align` is zero.
 #[inline]
 pub(crate) fn is_aligned_to(ptr: *const (), align: usize) -> bool {
-  // This is in a way better than `ptr as usize % align == 0`,
-  // because casting a pointer to an integer has the side effect that it exposes
-  // the pointer's provenance, which may theoretically inhibit some compiler
-  // optimizations.
-  ptr.align_offset(align) == 0
+  #[cfg(feature = "align_offset")]
+  {
+    // This is in a way better than `ptr as usize % align == 0`,
+    // because casting a pointer to an integer has the side effect that it
+    // exposes the pointer's provenance, which may theoretically inhibit
+    // some compiler optimizations.
+    ptr.align_offset(align) == 0
+  }
+  #[cfg(not(feature = "align_offset"))]
+  {
+    ((ptr as usize) % align) == 0
+  }
 }
 
 /// Re-interprets `&[u8]` as `&T`.