Make PCG thread safe

Author: ciaranra

Cargo.lock

@@ -15,7 +15,6 @@ readme = "README.md"
 
 [build-dependencies]
 cc.workspace = true
-ureq = { version = "2.9", default-features = false, features = ["native-tls"] }
 
 [lints]
 workspace = true

crates/pecos-clib-pcg/Cargo.toml

@@ -1,63 +1,23 @@
 use cc::Build;
 use std::env;
-use std::fs;
-use std::path::{Path, PathBuf};
+use std::path::PathBuf;
 
-// TODO: Should probably just vendor the C code into the Rust crate...
 fn main() {
-    let out_dir = PathBuf::from(env::var("OUT_DIR").unwrap());
     let manifest_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
-
-    // Try local path first (for development)
-    let local_clib_path = manifest_dir
-        .parent()
-        .unwrap()
-        .parent()
-        .unwrap()
-        .join("clib")
-        .join("pecos-rng");
-
-    let src_path = if local_clib_path.exists() {
-        // Development: use local files
-        let src = local_clib_path.join("src");
-        println!("cargo:rerun-if-changed={}", src.join("rng_pcg.c").display());
-        println!("cargo:rerun-if-changed={}", src.join("rng_pcg.h").display());
-        src
-    } else {
-        // Published crate: download from GitHub
-        let pcg_dir = out_dir.join("pcg");
-        fs::create_dir_all(&pcg_dir).unwrap();
-
-        let commit = "95a6ddbdf85ad7bcf8b9133aa2552f3f1ae7da84";
-        let base_url = format!(
-            "https://raw.githubusercontent.com/PECOS-packages/PECOS/{commit}/clib/pecos-rng/src"
-        );
-
-        // Download files if they don't exist
-        download_if_needed(&pcg_dir.join("rng_pcg.c"), &format!("{base_url}/rng_pcg.c"));
-        download_if_needed(&pcg_dir.join("rng_pcg.h"), &format!("{base_url}/rng_pcg.h"));
-
-        pcg_dir
-    };
+    let c_src_dir = manifest_dir.join("c_src");
+
+    // Build our local C code with thread-safe functions exposed
+    println!(
+        "cargo:rerun-if-changed={}",
+        c_src_dir.join("rng_pcg.c").display()
+    );
+    println!(
+        "cargo:rerun-if-changed={}",
+        c_src_dir.join("rng_pcg.h").display()
+    );
 
     Build::new()
-        .file(src_path.join("rng_pcg.c"))
-        .include(&src_path)
+        .file(c_src_dir.join("rng_pcg.c"))
+        .include(&c_src_dir)
         .compile("pecos_pcg");
 }
-
-fn download_if_needed(path: &Path, url: &str) {
-    if !path.exists() {
-        println!("cargo:warning=Downloading {} to {}", url, path.display());
-
-        let response = ureq::get(url)
-            .call()
-            .unwrap_or_else(|e| panic!("Failed to download {url}: {e}"));
-
-        let mut file = fs::File::create(path)
-            .unwrap_or_else(|e| panic!("Failed to create {}: {}", path.display(), e));
-
-        std::io::copy(&mut response.into_reader(), &mut file)
-            .unwrap_or_else(|e| panic!("Failed to write {}: {}", path.display(), e));
-    }
-}

crates/pecos-clib-pcg/build.rs

@@ -0,0 +1,92 @@
+/*
+ * PCG Random Number Generation for C.
+ *
+ * Copyright 2014 Melissa O'Neill <oneill@pcg-random.org>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * For additional information about the PCG random number generation scheme,
+ * including its license and other licensing options, visit
+ *
+ *       http://www.pcg-random.org
+ */
+
+#include <math.h>
+#include "rng_pcg.h"
+
+// RNG state structure is now defined in the header
+
+// global RNG state
+static pcg32_random_t pcg32_global = {
+    0x853c49e6748fea9bULL,
+    0xda3e39cb94b95bdbULL
+};
+
+// default multi[plier]
+#define PCG_DEFAULT_MULTIPLIER_64  6364136223846793005ULL
+
+// helper functions
+static inline uint32_t pcg_rotr_32(uint32_t value, unsigned int urot) {
+    int rot = (int)urot;
+    return (value >> rot) | (value << ((-rot) & 31));
+}
+
+static inline void pcg_setseq_64_step_r(pcg32_random_t* rng) {
+    rng->state = rng->state * PCG_DEFAULT_MULTIPLIER_64 + rng->inc;
+}
+
+static inline uint32_t pcg_output_xsh_rr_64_32(uint64_t state) {
+    return pcg_rotr_32(((state >> 18u) ^ state) >> 27u, state >> 59u);
+}
+
+uint32_t pcg32_random_r(pcg32_random_t* rng) {
+    const uint64_t oldstate = rng->state;
+    pcg_setseq_64_step_r(rng);
+    return pcg_output_xsh_rr_64_32(oldstate);
+}
+
+uint32_t pcg32_boundedrand_r(pcg32_random_t* rng, uint32_t ubound) {
+    int32_t bound = (int32_t)ubound;
+    uint32_t threshold = -bound % bound;
+    for (;;) {
+        const uint32_t r = pcg32_random_r(rng);
+        if (r >= threshold)
+            return r % bound;
+    }
+}
+
+void pcg32_srandom_r(pcg32_random_t* rng, uint64_t initstate, uint64_t initseq) {
+    rng->state = 0U;
+    rng->inc = (initseq << 1u) | 1u;
+    pcg_setseq_64_step_r(rng);
+    rng->state += initstate;
+    pcg_setseq_64_step_r(rng);
+}
+
+// public interface to RNG
+
+uint32_t pcg32_random() {
+    return pcg32_random_r(&pcg32_global);
+}
+
+uint32_t pcg32_boundedrand(uint32_t bound) {
+    return pcg32_boundedrand_r(&pcg32_global, bound);
+}
+
+double pcg32_frandom() {
+    return ldexp(pcg32_random(), -32);
+}
+
+void pcg32_srandom(uint64_t seq) {
+    pcg32_srandom_r(&pcg32_global, 42u, seq);
+}

crates/pecos-clib-pcg/c_src/rng_pcg.c

@@ -0,0 +1,51 @@
+/*
+ * PCG Random Number Generation for C.
+ *
+ * Copyright 2014 Melissa O'Neill <oneill@pcg-random.org>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * For additional information about the PCG random number generation scheme,
+ * including its license and other licensing options, visit
+ *
+ *       http://www.pcg-random.org
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#if __cplusplus
+extern "C" {
+#endif
+
+// Thread-safe RNG state structure
+typedef struct pcg_state_setseq_64 {
+    uint64_t state;
+    uint64_t inc;
+} pcg32_random_t;
+
+// Thread-safe versions that take explicit state
+uint32_t pcg32_random_r(pcg32_random_t* rng);
+uint32_t pcg32_boundedrand_r(pcg32_random_t* rng, uint32_t bound);
+void pcg32_srandom_r(pcg32_random_t* rng, uint64_t initstate, uint64_t initseq);
+
+// Global state versions (for compatibility)
+uint32_t pcg32_random();
+uint32_t pcg32_boundedrand(uint32_t bound);
+double pcg32_frandom();
+void pcg32_srandom(uint64_t seq);
+
+#if __cplusplus
+}
+#endif

crates/pecos-clib-pcg/c_src/rng_pcg.h

@@ -1,29 +1,81 @@
-// FFI bindings to the C PCG library
+use std::cell::RefCell;
+
+// Mirror the C struct pcg32_random_t
+#[repr(C)]
+struct PcgState {
+    state: u64,
+    inc: u64,
+}
+
+// FFI bindings to the C PCG library - now with thread-safe versions!
 unsafe extern "C" {
-    fn pcg32_random() -> u32;
-    fn pcg32_boundedrand(bound: u32) -> u32;
-    fn pcg32_frandom() -> f64;
-    fn pcg32_srandom(seq: u64);
+    fn pcg32_random_r(rng: *mut PcgState) -> u32;
+    fn pcg32_boundedrand_r(rng: *mut PcgState, bound: u32) -> u32;
+    fn pcg32_srandom_r(rng: *mut PcgState, initstate: u64, initseq: u64);
+}
+
+// Thread-local state: each thread has its own PCG state
+thread_local! {
+    static THREAD_STATE: RefCell<ThreadRngState> = RefCell::new(ThreadRngState::new());
+}
+
+struct ThreadRngState {
+    pcg: PcgState,
+    seed: u64,
+}
+
+impl ThreadRngState {
+    fn new() -> Self {
+        let mut state = Self {
+            pcg: PcgState { state: 0, inc: 0 },
+            seed: 0,
+        };
+        // Initialize with default seed
+        state.reseed(42);
+        state
+    }
+
+    fn reseed(&mut self, seed: u64) {
+        self.seed = seed;
+        unsafe {
+            // For PCG: initstate affects starting position, initseq selects sequence
+            // Using seed for initseq (sequence selection) and a fixed initstate
+            // matches the original behavior while allowing different sequences per thread
+            pcg32_srandom_r(&raw mut self.pcg, 42, seed);
+        }
+    }
 }
 
 // Rust wrapper functions with safe interfaces
 #[must_use]
 pub fn random() -> u32 {
-    unsafe { pcg32_random() }
+    THREAD_STATE.with(|state| {
+        let mut state = state.borrow_mut();
+        unsafe { pcg32_random_r(&raw mut state.pcg) }
+    })
 }
 
 #[must_use]
 pub fn boundedrand(bound: u32) -> u32 {
-    unsafe { pcg32_boundedrand(bound) }
+    THREAD_STATE.with(|state| {
+        let mut state = state.borrow_mut();
+        unsafe { pcg32_boundedrand_r(&raw mut state.pcg, bound) }
+    })
 }
 
 #[must_use]
 pub fn frandom() -> f64 {
-    unsafe { pcg32_frandom() }
+    // The C code implements this as ldexp(pcg32_random(), -32)
+    // which is equivalent to dividing by 2^32
+    THREAD_STATE.with(|state| {
+        let mut state = state.borrow_mut();
+        let val = unsafe { pcg32_random_r(&raw mut state.pcg) };
+        f64::from(val) * 2.0_f64.powi(-32)
+    })
 }
 
 pub fn srandom(seq: u64) {
-    unsafe { pcg32_srandom(seq) }
+    THREAD_STATE.with(|state| state.borrow_mut().reseed(seq));
 }
 
 #[cfg(test)]