From 70cb75c31e5d084da3a06457484096330ca72a61 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Thu, 26 Jul 2018 18:29:38 +0200
Subject: [PATCH 1/2] make memrchr use align_offset

---
 src/libcore/slice/memchr.rs | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/libcore/slice/memchr.rs b/src/libcore/slice/memchr.rs
index 7b62e7b0620fd..dbbe1c07c2338 100644
--- a/src/libcore/slice/memchr.rs
+++ b/src/libcore/slice/memchr.rs
@@ -102,8 +102,24 @@ pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
     let ptr = text.as_ptr();
     let usize_bytes = mem::size_of::<usize>();
 
+    // a version of align_offset that says how much must be *subtracted*
+    // from a pointer to be aligned.
+    #[inline(always)]
+    fn align_offset_down(ptr: *const u8, align: usize) -> usize {
+        let align_offset = ptr.align_offset(align);
+        if align_offset > align {
+            // Not possible to align
+            usize::max_value()
+        } else if align_offset == 0 {
+            0
+        } else {
+            // E.g. if align=8 and we have to add 1, then we can also subtract 7.
+            align - align_offset
+        }
+    }
+
     // search to an aligned boundary
-    let end_align = (ptr as usize + len) & (usize_bytes - 1);
+    let end_align = align_offset_down(unsafe { ptr.offset(len as isize) }, usize_bytes);
     let mut offset;
     if end_align > 0 {
         offset = if end_align >= len { 0 } else { len - end_align };

From 3bc59b5205410b229eb66236b4aafbb90487fa34 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Fri, 27 Jul 2018 11:54:38 +0200
Subject: [PATCH 2/2] use slice::align_to

---
 src/libcore/slice/memchr.rs | 33 +++++++--------------------------
 1 file changed, 7 insertions(+), 26 deletions(-)

diff --git a/src/libcore/slice/memchr.rs b/src/libcore/slice/memchr.rs
index dbbe1c07c2338..72e7b57a6cb3c 100644
--- a/src/libcore/slice/memchr.rs
+++ b/src/libcore/slice/memchr.rs
@@ -102,32 +102,13 @@ pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
     let ptr = text.as_ptr();
     let usize_bytes = mem::size_of::<usize>();
 
-    // a version of align_offset that says how much must be *subtracted*
-    // from a pointer to be aligned.
-    #[inline(always)]
-    fn align_offset_down(ptr: *const u8, align: usize) -> usize {
-        let align_offset = ptr.align_offset(align);
-        if align_offset > align {
-            // Not possible to align
-            usize::max_value()
-        } else if align_offset == 0 {
-            0
-        } else {
-            // E.g. if align=8 and we have to add 1, then we can also subtract 7.
-            align - align_offset
-        }
-    }
-
-    // search to an aligned boundary
-    let end_align = align_offset_down(unsafe { ptr.offset(len as isize) }, usize_bytes);
-    let mut offset;
-    if end_align > 0 {
-        offset = if end_align >= len { 0 } else { len - end_align };
-        if let Some(index) = text[offset..].iter().rposition(|elt| *elt == x) {
-            return Some(offset + index);
-        }
-    } else {
-        offset = len;
+    let mut offset = {
+        // We call this just to obtain the length of the suffix
+        let (_, _, suffix) = unsafe { text.align_to::<usize>() };
+        len - suffix.len()
+    };
+    if let Some(index) = text[offset..].iter().rposition(|elt| *elt == x) {
+        return Some(offset + index);
     }
 
     // search the body of the text