chore: remove "runtime" mode

not much point come to think of it -- portable should include any runtime optimizations.

Author: nyurik

Cargo.toml

@@ -31,8 +31,6 @@ _all_compatible = ["cpp_portable", "rust"]
 cpp_portable = ["cpp"]
 # Optimize FastPFOR for the current CPU.
 cpp_native = ["cpp"]
-# Experimental mode for dynamic dispatch of FastPFOR implementations.
-cpp_runtime = ["cpp"]
 cpp = ["dep:cmake", "dep:cxx", "dep:cxx-build"]
 rust = ["dep:thiserror", "dep:bytes"]
 

README.md

@@ -58,9 +58,8 @@ The C++ backend can be compiled with different SIMD instruction sets. Control th
 |------|-------------|
 | `cpp_portable` | **Default.** Uses SSE4.2 baseline only. Binaries run on any x86-64 CPU from ~2008+. Best for distributable libraries. |
 | `cpp_native` | Uses `-march=native` to enable all SIMD instructions supported by the build machine (AVX, AVX2, etc.). Maximum performance but may crash on CPUs lacking those instructions. |
-| `cpp_runtime` | Experimental. Reserved for future runtime CPU dispatch. |
 
-Feature selection can be overridden with the `FASTPFOR_SIMD_MODE` environment variable set to "portable", "native", or "runtime".
+Feature selection can be overridden with the `FASTPFOR_SIMD_MODE` environment variable set to "portable" or "native".
 
 **Recommendation:** Use `portable` (default) for libraries and distributed binaries. Use `native` only when building for a specific machine where you need maximum performance.
 

build.rs

@@ -17,7 +17,6 @@ fn build_fastpfor() {
     // Warn if more than one feature is enabled. The order is important, must match the if else block below.
     let simd_features = [
         (cfg!(feature = "cpp_portable"), "'cpp_portable'"),
-        (cfg!(feature = "cpp_runtime"), "'cpp_runtime'"),
         (cfg!(feature = "cpp_native"), "'cpp_native'"),
     ];
     let enabled_simd_features: Vec<_> = simd_features
@@ -28,7 +27,6 @@ fn build_fastpfor() {
     // SIMD mode configuration via environment variable:
     // - native: Use -march=native for maximum performance (not portable across CPUs)
     // - portable: Use baseline SSE4.2 only for maximum compatibility (default)
-    // - runtime: Use function multi-versioning for runtime CPU dispatch (experimental)
     let simd_mode = env::var("FASTPFOR_SIMD_MODE");
     if enabled_simd_features.len() > 1 {
         let feats = enabled_simd_features.join(", ");
@@ -49,8 +47,6 @@ fn build_fastpfor() {
             // The order is important, must match the list above.
             if cfg!(feature = "cpp_portable") {
                 "portable"
-            } else if cfg!(feature = "cpp_runtime") {
-                "runtime"
             } else if cfg!(feature = "cpp_native") {
                 "native"
             } else {

justfile

@@ -116,7 +116,7 @@ test:
     cargo test --workspace --all-targets --features _all_compatible
     cargo test --workspace --doc --features _all_compatible
 
-# Test with a specific SIMD mode (portable, native, or runtime)
+# Test with a specific SIMD mode (portable, native)
 test-simd mode='portable':
     cargo test --workspace --all-targets --features cpp_{{mode}}
 
@@ -126,8 +126,6 @@ test-all-simd-modes:
     {{just}} test-simd portable
     cargo clean -p fastpfor
     {{just}} test-simd native
-    cargo clean -p fastpfor
-    {{just}} test-simd runtime
 
 # Test documentation generation
 test-doc:  (docs '')