chore: hide avx512 behind feature flag

Cargo.toml

@@ -5,7 +5,7 @@ members = ["cpu-features"]
 name = "json-escape-simd"
 version = "3.0.0"
 edition = "2024"
-rust-version = "1.89.0"
+rust-version = "1.85.0"
 include = ["src/**/*.rs"]
 description = "Optimized SIMD routines for escaping JSON strings."
 license = "MIT"
@@ -18,6 +18,7 @@ path = "examples/escape.rs"
 
 [features]
 codspeed = ["criterion2/codspeed"]
+avx512 = []
 asan = [] # for ASAN
 
 [[bench]]

src/lib.rs

@@ -297,9 +297,13 @@ fn format_string(value: &str, dst: &mut [u8]) -> usize {
 
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     {
-        if is_x86_feature_detected!("avx512f") {
-            unsafe { simd::avx512::format_string(value, dst) }
-        } else if is_x86_feature_detected!("avx2") {
+        #[cfg(feature = "avx512")]
+        {
+            if is_x86_feature_detected!("avx512f") {
+                return unsafe { simd::avx512::format_string(value, dst) };
+            }
+        }
+        if is_x86_feature_detected!("avx2") {
             unsafe { simd::avx2::format_string(value, dst) }
         } else if is_x86_feature_detected!("sse2") {
             unsafe { simd::sse2::format_string(value, dst) }

src/simd/mod.rs

@@ -2,7 +2,7 @@
 
 #[cfg(any(target_arch = "x86_64", target_arch = "x86"))]
 pub(crate) mod avx2;
-#[cfg(any(target_arch = "x86_64", target_arch = "x86"))]
+#[cfg(all(any(target_arch = "x86_64", target_arch = "x86"), feature = "avx512"))]
 pub(crate) mod avx512;
 pub mod bits;
 #[cfg(target_arch = "aarch64")]