change: Move from maybe_rayon to rayon-1.8 (privacy-scaling-explo…

…rations#122)

* change: Move from `maybe_rayon` to `rayon-1.8`

After seeing the issues with WASM that the last release (`0.5.0`) of
this crate made, the idea is to now control the compatibility with WASM
while at the same time, making it easy to handle.

In this line of work, the idea was to simply do the following:
- Use `rayon 1.8` as a dependency for paralellism which fixes the WASM
  compat issues with `multicore`-related things. See: rayon-rs/rayon#1019
  thanks @han0110 for the suggestion.
- Use conditional dev-dependency loading for `getrandom` such that we
  can compile the lib for WASM-targets in the CI without needing to have
  the dependency being pulled downstream.
- The `multicore` module is gone, and the rest of the code has been
  refactored since the "fallback" is now handled by rayon itself.

* change: Update CI to account for WASM compat

* chore: Add paralellism section to README

* chore: Fix CI missing "

* chore:  Split WASM build & add targets

* chore: Test all features for regular-target  builds

* chore: Address review nits

.github/workflows/ci.yml

@@ -34,15 +34,36 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  compat:
+    if: github.event.pull_request.draft == false
+    name: Wasm-compatibility
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        target:
+          - wasm32-unknown-unknown
+          - wasm32-wasi
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+
+      - name: Download WASM targets
+        run: rustup target add "${{ matrix.target }}"
+      # We run WASM build (for tests) which compiles the lib allowig us to have
+      # `getrandom` as a dev-dependency.
+      - name: Build
+        run: cargo build --tests --release --features "bn256-table derive_serde prefetch" --target "${{ matrix.target }}"
   test:
     if: github.event.pull_request.draft == false
     name: Test
     runs-on: ubuntu-latest
     strategy:
       matrix:
         include:
-          - feature:
           - feature: default
+          - feature: bn256-table
+          - feature: derive_serde
+          - feature: asm
     steps:
       - uses: actions/checkout@v2
       - uses: actions-rs/toolchain@v1

Cargo.toml

@@ -19,6 +19,11 @@ hex = "0.4"
 rand_chacha = "0.3.1"
 sha3 = "0.10.8"
 
+# Added to make sure we are able to build the lib in the CI.
+# Notice this will never be loaded for someone using this lib as dep.
+[target.'cfg(all(target_arch = "wasm32", target_os = "unknown"))'.dev-dependencies]
+getrandom = { version = "0.2", features = ["js"] }
+
 [dependencies]
 subtle = "2.4"
 ff = { version = "0.13.0", default-features = false, features = ["std"] }
@@ -36,13 +41,12 @@ serde = { version = "1.0", default-features = false, optional = true }
 serde_arrays = { version = "0.1.0", optional = true }
 hex = { version = "0.4", optional = true, default-features = false, features = ["alloc", "serde"] }
 blake2b_simd = "1"
-maybe-rayon = { version = "0.1.0", default-features = false }
+rayon = "1.8"
 digest = "0.10.7"
 sha2 = "0.10.8"
 
 [features]
-default = ["bits", "multicore", "bn256-table", "derive_serde"]
-multicore = ["maybe-rayon/threads"]
+default = ["bits", "bn256-table", "derive_serde"]
 asm = []
 bits = ["ff/bits"]
 bn256-table = []

README.md

@@ -13,6 +13,19 @@ The implementations were originally ported from [matterlabs/pairing](https://git
 * Various features related to serialization and deserialization of curve points and field elements.
 * Curve-specific optimizations and benchmarking capabilities.
 
+## Controlling parallelism
+
+`halo2curves` currently uses [rayon](https://github.com/rayon-rs/rayon) for parallel
+computation. 
+
+The `RAYON_NUM_THREADS` environment variable can be used to set the number of
+threads.
+
+When compiling to WASM-targets, notice that since version `1.7`, `rayon` will fallback automatically (with no need to handle features) to require `getrandom` in order to be able to work.
+For more info related to WASM-compilation.
+
+See: [Rayon: Usage with WebAssembly](https://github.com/rayon-rs/rayon#usage-with-webassembly) for more info.  
+
 ## Benchmarks
 
 Benchmarking is supported through the use of Rust's built-in test framework. Benchmarks can be run without assembly optimizations:

src/fft.rs

@@ -1,4 +1,3 @@
-use crate::multicore;
 pub use crate::{CurveAffine, CurveExt};
 use ff::Field;
 use group::{GroupOpsOwned, ScalarMulOwned};
@@ -38,7 +37,7 @@ pub fn best_fft<Scalar: Field, G: FftGroup<Scalar>>(a: &mut [G], omega: Scalar,
         r
     }
 
-    let threads = multicore::current_num_threads();
+    let threads = rayon::current_num_threads();
     let log_threads = threads.ilog2();
     let n = a.len();
     assert_eq!(n, 1 << log_n);
@@ -107,7 +106,7 @@ pub fn recursive_butterfly_arithmetic<Scalar: Field, G: FftGroup<Scalar>>(
         a[1] -= &t;
     } else {
         let (left, right) = a.split_at_mut(n / 2);
-        multicore::join(
+        rayon::join(
             || recursive_butterfly_arithmetic(left, n / 2, twiddle_chunk * 2, twiddles),
             || recursive_butterfly_arithmetic(right, n / 2, twiddle_chunk * 2, twiddles),
         );

src/lib.rs

@@ -3,7 +3,6 @@ pub mod ff_ext;
 pub mod fft;
 pub mod hash_to_curve;
 pub mod msm;
-pub mod multicore;
 pub mod serde;
 
 pub mod bls12_381;

src/msm.rs

@@ -4,8 +4,6 @@ use ff::PrimeField;
 use group::Group;
 use pasta_curves::arithmetic::CurveAffine;
 
-use crate::multicore;
-
 fn get_booth_index(window_index: usize, window_size: usize, el: &[u8]) -> i32 {
     // Booth encoding:
     // * step by `window` size
@@ -155,12 +153,12 @@ pub fn small_multiexp<C: CurveAffine>(coeffs: &[C::Scalar], bases: &[C]) -> C::C
 pub fn best_multiexp<C: CurveAffine>(coeffs: &[C::Scalar], bases: &[C]) -> C::Curve {
     assert_eq!(coeffs.len(), bases.len());
 
-    let num_threads = multicore::current_num_threads();
+    let num_threads = rayon::current_num_threads();
     if coeffs.len() > num_threads {
         let chunk = coeffs.len() / num_threads;
         let num_chunks = coeffs.chunks(chunk).len();
         let mut results = vec![C::Curve::identity(); num_chunks];
-        multicore::scope(|scope| {
+        rayon::scope(|scope| {
             let chunk = coeffs.len() / num_threads;
 
             for ((coeffs, bases), acc) in coeffs
@@ -186,10 +184,7 @@ mod test {
 
     use std::ops::Neg;
 
-    use crate::{
-        bn256::{Fr, G1Affine, G1},
-        multicore,
-    };
+    use crate::bn256::{Fr, G1Affine, G1};
     use ark_std::{end_timer, start_timer};
     use ff::{Field, PrimeField};
     use group::{Curve, Group};
@@ -200,12 +195,12 @@ mod test {
     fn best_multiexp<C: CurveAffine>(coeffs: &[C::Scalar], bases: &[C]) -> C::Curve {
         assert_eq!(coeffs.len(), bases.len());
 
-        let num_threads = multicore::current_num_threads();
+        let num_threads = rayon::current_num_threads();
         if coeffs.len() > num_threads {
             let chunk = coeffs.len() / num_threads;
             let num_chunks = coeffs.chunks(chunk).len();
             let mut results = vec![C::Curve::identity(); num_chunks];
-            multicore::scope(|scope| {
+            rayon::scope(|scope| {
                 let chunk = coeffs.len() / num_threads;
 
                 for ((coeffs, bases), acc) in coeffs