From 1c08e004e5d62e7fad8167009c315785297b1ad8 Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Sun, 1 Feb 2026 20:58:34 -0700
Subject: [PATCH 1/2] aes: use `cpubits` crate

The `cpubits` crate contains a macro for selecting between 32-bit and
64-bit backends, incorporating 64-bit overrides for certain natively
32-bit targets with native ISA support for operations "register pairs",
namely ARMv7 and WASM. It also supports overriding the selection with
`cfg(cpubits = "...")`

This switches the selection of the 32-bit vs 64-bit soft backend, always
compiled into the crate as it's used as a fallback implementation if
intrinsics aren't available, to using `cpubits`.

The crate contains a vendored copy of `cfg-if`, so this also replaces
`cfg-if` as a dependency with `cpubits`.
---
 Cargo.lock      |  8 +++++++-
 aes/Cargo.toml  | 10 ++++++++--
 aes/src/lib.rs  |  4 +---
 aes/src/soft.rs | 13 ++++++++++---
 4 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index c2da1658..06f5d0f9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -6,8 +6,8 @@ version = 4
 name = "aes"
 version = "0.9.0-rc.3"
 dependencies = [
- "cfg-if",
  "cipher",
+ "cpubits",
  "cpufeatures",
  "hex-literal",
  "zeroize",
@@ -102,6 +102,12 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "cpubits"
+version = "0.1.0-rc.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "11a8c0210fa48ba3ea04ac1e9c6e72ae66009db3b1f1745635d4ff2e58eaadd0"
+
 [[package]]
 name = "cpufeatures"
 version = "0.2.17"
diff --git a/aes/Cargo.toml b/aes/Cargo.toml
index ab0d7b7b..63c349c4 100644
--- a/aes/Cargo.toml
+++ b/aes/Cargo.toml
@@ -13,8 +13,8 @@ keywords = ["crypto", "aes", "rijndael", "block-cipher"]
 categories = ["cryptography", "no-std"]
 
 [dependencies]
-cfg-if = "1"
 cipher = "0.5.0-rc.7"
+cpubits = "0.1.0-rc.3"
 zeroize = { version = "1.5.6", optional = true, default-features = false, features = ["aarch64"] }
 
 [target.'cfg(any(target_arch = "aarch64", target_arch = "x86_64", target_arch = "x86"))'.dependencies]
@@ -29,7 +29,13 @@ hazmat = [] # Expose cryptographically hazardous APIs
 
 [lints.rust.unexpected_cfgs]
 level = "warn"
-check-cfg = ["cfg(aes_compact)", "cfg(aes_force_soft)", "cfg(aes_avx256)", "cfg(aes_avx512)"]
+check-cfg = [
+    'cfg(aes_compact)',
+    'cfg(aes_force_soft)',
+    'cfg(aes_avx256)',
+    'cfg(aes_avx512)',
+    'cfg(cpubits, values("16", "32", "64"))'
+]
 
 [package.metadata.docs.rs]
 all-features = true
diff --git a/aes/src/lib.rs b/aes/src/lib.rs
index b2e80a6c..ed562871 100644
--- a/aes/src/lib.rs
+++ b/aes/src/lib.rs
@@ -129,9 +129,7 @@ pub mod hazmat;
 mod macros;
 mod soft;
 
-use cfg_if::cfg_if;
-
-cfg_if! {
+cpubits::cfg_if! {
     if #[cfg(all(target_arch = "aarch64", not(aes_force_soft)))] {
         mod armv8;
         mod autodetect;
diff --git a/aes/src/soft.rs b/aes/src/soft.rs
index 1f0941cb..658d8ff7 100644
--- a/aes/src/soft.rs
+++ b/aes/src/soft.rs
@@ -8,9 +8,16 @@
 
 #![deny(unsafe_code)]
 
-#[cfg_attr(not(target_pointer_width = "64"), path = "soft/fixslice32.rs")]
-#[cfg_attr(target_pointer_width = "64", path = "soft/fixslice64.rs")]
-pub(crate) mod fixslice;
+cpubits::cpubits! {
+    16 | 32 => {
+        #[path = "soft/fixslice32.rs"]
+        pub(crate) mod fixslice;
+    }
+    64 => {
+        #[path = "soft/fixslice32.rs"]
+        pub(crate) mod fixslice;
+    }
+}
 
 use crate::Block;
 use cipher::{

From 0577582661335a3e76aaaf3f79acec136a317aa3 Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Sun, 1 Feb 2026 21:17:15 -0700
Subject: [PATCH 2/2] Update aes/src/soft.rs

Co-authored-by: Artyom Pavlov <newpavlov@gmail.com>
---
 aes/src/soft.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/aes/src/soft.rs b/aes/src/soft.rs
index 658d8ff7..445adc39 100644
--- a/aes/src/soft.rs
+++ b/aes/src/soft.rs
@@ -14,7 +14,7 @@ cpubits::cpubits! {
         pub(crate) mod fixslice;
     }
     64 => {
-        #[path = "soft/fixslice32.rs"]
+        #[path = "soft/fixslice64.rs"]
         pub(crate) mod fixslice;
     }
 }