Make char::is_ascii_whitespace branchless on 32 and 64-bit targets

.mailmap

@@ -160,7 +160,8 @@ Kyle J Strand <[email protected]> <[email protected]>
 Kyle J Strand <[email protected]> <[email protected]>
 Kyle J Strand <[email protected]> <[email protected]>
 Kyle J Strand <[email protected]> <[email protected]>
-Laurențiu Nicola <[email protected]>
+Laurențiu Nicola <[email protected]> Laurentiu Nicola <[email protected]>
+Laurențiu Nicola <[email protected]> <[email protected]>
 Lee Jeffery <[email protected]> Lee Jeffery <[email protected]>
 Lee Wondong <[email protected]>
 Lennart Kudling <[email protected]>

library/core/src/char/methods.rs

@@ -1544,9 +1544,23 @@ impl char {
     #[rustc_const_stable(feature = "const_ascii_ctype_on_intrinsics", since = "1.47.0")]
     #[inline]
     pub const fn is_ascii_whitespace(&self) -> bool {
-        match *self {
-            '\t' | '\n' | '\x0C' | '\r' | ' ' => true,
-            _ => false,
+        #[cfg(not(target_pointer_width = "16"))]
+        {
+            // Inspired from https://pdimov.github.io/blog/2020/07/19/llvm-and-memchr/
+            const MASK: u32 = 1 << (b'\t' - 1)
+                | 1 << (b'\n' - 1)
+                | 1 << (b'\x0C' - 1)
+                | 1 << (b'\r' - 1)
+                | 1 << (b' ' - 1);
+            let ch = (*self as u32).wrapping_sub(1);
+            ch < (' ' as u32) && 1 << (ch as u8) & MASK != 0
+        }
+        #[cfg(target_pointer_width = "16")]
+        {
+            match *self {
+                '\t' | '\n' | '\x0C' | '\r' | ' ' => true,
+                _ => false,
+            }
         }
     }