From 93f503166d068f97ad298a45fe48292fb14c2afa Mon Sep 17 00:00:00 2001
From: Folkert de Vries <folkert@folkertdev.nl>
Date: Mon, 17 Feb 2025 19:35:01 +0100
Subject: [PATCH] apply the `crc` target feature to the acle crc32
 implementation

---
 zlib-rs/src/crc32.rs      | 18 +++-------
 zlib-rs/src/crc32/acle.rs | 72 ++++++---------------------------------
 2 files changed, 15 insertions(+), 75 deletions(-)

diff --git a/zlib-rs/src/crc32.rs b/zlib-rs/src/crc32.rs
index a936d094..f3990ebd 100644
--- a/zlib-rs/src/crc32.rs
+++ b/zlib-rs/src/crc32.rs
@@ -52,24 +52,14 @@ impl Crc32Fold {
         }
     }
 
-    #[cfg_attr(not(target_arch = "x86_64"), allow(unused))]
-    pub(crate) fn is_pclmulqdq_enabled() -> bool {
-        crate::cpu_features::is_enabled_pclmulqdq()
-    }
-
-    #[cfg_attr(not(target_arch = "aarch64"), allow(unused))]
-    pub(crate) fn is_crc_enabled() -> bool {
-        crate::cpu_features::is_enabled_crc()
-    }
-
     pub fn fold(&mut self, src: &[u8], _start: u32) {
         #[cfg(target_arch = "x86_64")]
-        if Self::is_pclmulqdq_enabled() {
+        if crate::cpu_features::is_enabled_pclmulqdq() {
             return unsafe { self.fold.fold(src, _start) };
         }
 
         #[cfg(target_arch = "aarch64")]
-        if Self::is_crc_enabled() {
+        if crate::cpu_features::is_enabled_crc() {
             self.value = unsafe { self::acle::crc32_acle_aarch64(self.value, src) };
             return;
         }
@@ -80,7 +70,7 @@ impl Crc32Fold {
 
     pub fn fold_copy(&mut self, dst: &mut [u8], src: &[u8]) {
         #[cfg(target_arch = "x86_64")]
-        if Self::is_pclmulqdq_enabled() {
+        if crate::cpu_features::is_enabled_pclmulqdq() {
             return unsafe { self.fold.fold_copy(dst, src) };
         }
 
@@ -90,7 +80,7 @@ impl Crc32Fold {
 
     pub fn finish(self) -> u32 {
         #[cfg(target_arch = "x86_64")]
-        if Self::is_pclmulqdq_enabled() {
+        if crate::cpu_features::is_enabled_pclmulqdq() {
             return unsafe { self.fold.finish() };
         }
 
diff --git a/zlib-rs/src/crc32/acle.rs b/zlib-rs/src/crc32/acle.rs
index 347a6f7a..bf89692c 100644
--- a/zlib-rs/src/crc32/acle.rs
+++ b/zlib-rs/src/crc32/acle.rs
@@ -3,6 +3,7 @@
 //! The functions in this module must only be executed on an ARM system with the CRC feature.
 
 #[cfg_attr(not(target_arch = "aarch64"), allow(unused))]
+#[target_feature(enable = "crc")]
 pub unsafe fn crc32_acle_aarch64(crc: u32, buf: &[u8]) -> u32 {
     let mut c = !crc;
 
@@ -24,29 +25,9 @@ pub unsafe fn crc32_acle_aarch64(crc: u32, buf: &[u8]) -> u32 {
     !c
 }
 
-#[cfg_attr(not(target_arch = "arm"), allow(unused))]
-pub unsafe fn crc32_acle_arm(crc: u32, buf: &[u8]) -> u32 {
-    let mut c = !crc;
-
-    // SAFETY: [u8; 4] safely transmutes into u32.
-    let (before, middle, after) = unsafe { buf.align_to::<u32>() };
-
-    c = remainder(c, before);
-
-    if middle.is_empty() && after.is_empty() {
-        return !c;
-    }
-
-    for w in middle {
-        c = unsafe { __crc32w(c, *w) };
-    }
-
-    c = remainder(c, after);
-
-    !c
-}
-
-fn remainder(mut c: u32, mut buf: &[u8]) -> u32 {
+#[inline]
+#[target_feature(enable = "crc")]
+unsafe fn remainder(mut c: u32, mut buf: &[u8]) -> u32 {
     if let [b0, b1, b2, b3, rest @ ..] = buf {
         c = unsafe { __crc32w(c, u32::from_le_bytes([*b0, *b1, *b2, *b3])) };
         buf = rest;
@@ -67,6 +48,9 @@ fn remainder(mut c: u32, mut buf: &[u8]) -> u32 {
     c
 }
 
+// FIXME the intrinsics below are stable since rust 1.80.0: remove these and use the standard
+// library versions once our MSRV reaches that version.
+
 /// CRC32 single round checksum for bytes (8 bits).
 ///
 /// [Arm's documentation](https://developer.arm.com/architectures/instruction-sets/intrinsics/__crc32b)
@@ -115,18 +99,6 @@ unsafe fn __crc32d(mut crc: u32, data: u64) -> u32 {
     }
 }
 
-/// CRC32-C single round checksum for words (32 bits).
-///
-/// [Arm's documentation](https://developer.arm.com/architectures/instruction-sets/intrinsics/__crc32cw)
-#[target_feature(enable = "crc")]
-#[cfg_attr(target_arch = "arm", target_feature(enable = "v8"))]
-pub unsafe fn __crc32cw(mut crc: u32, data: u32) -> u32 {
-    unsafe {
-        core::arch::asm!("crc32cw {crc:w}, {crc:w}, {data:w}", crc = inout(reg) crc, data = in(reg) data);
-        crc
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -142,21 +114,11 @@ mod tests {
 
             a == b
         }
-
-        fn crc32_acle_arm_is_crc32fast(v: Vec<u8>, start: u32) -> bool {
-            let mut h = crc32fast::Hasher::new_with_initial(start);
-            h.update(&v);
-
-            let a = unsafe { crc32_acle_arm(start, &v) };
-            let b = h.finalize();
-
-            a == b
-        }
     }
 
     #[test]
     fn test_crc32b() {
-        if !crate::crc32::Crc32Fold::is_crc_enabled() {
+        if !crate::cpu_features::is_enabled_crc() {
             return;
         }
 
@@ -168,7 +130,7 @@ mod tests {
 
     #[test]
     fn test_crc32h() {
-        if !crate::crc32::Crc32Fold::is_crc_enabled() {
+        if !crate::cpu_features::is_enabled_crc() {
             return;
         }
 
@@ -180,7 +142,7 @@ mod tests {
 
     #[test]
     fn test_crc32w() {
-        if !crate::crc32::Crc32Fold::is_crc_enabled() {
+        if !crate::cpu_features::is_enabled_crc() {
             return;
         }
 
@@ -193,7 +155,7 @@ mod tests {
     #[test]
     #[cfg(target_arch = "aarch64")]
     fn test_crc32d() {
-        if !crate::crc32::Crc32Fold::is_crc_enabled() {
+        if !crate::cpu_features::is_enabled_crc() {
             return;
         }
 
@@ -202,16 +164,4 @@ mod tests {
             assert_eq!(__crc32d(0, 18446744073709551615), 1147535477);
         }
     }
-
-    #[test]
-    fn test_crc32cw() {
-        if !crate::crc32::Crc32Fold::is_crc_enabled() {
-            return;
-        }
-
-        unsafe {
-            assert_eq!(__crc32cw(0, 0), 0);
-            assert_eq!(__crc32cw(0, 4294967295), 3080238136);
-        }
-    }
 }