halo2_poseidon: Add no-std support

halo2_poseidon/Cargo.toml

@@ -15,8 +15,8 @@ readme = "README.md"
 categories = ["cryptography"]
 
 [dependencies]
-bitvec = "1"
-ff = "0.13"
+bitvec = { version = "1", default-features = false }
+ff = { version = "0.13", default-features = false }
 group = "0.13"
 pasta_curves = "0.5"
 

halo2_poseidon/src/grain.rs

@@ -1,6 +1,6 @@
 //! The Grain LFSR in self-shrinking mode, as used by Poseidon.
 
-use std::marker::PhantomData;
+use core::marker::PhantomData;
 
 use bitvec::prelude::*;
 use group::ff::{Field, FromUniformBytes, PrimeField};

halo2_poseidon/src/lib.rs

@@ -1,9 +1,16 @@
 //! The Poseidon algebraic hash function.
 
-use std::convert::TryInto;
-use std::fmt;
-use std::iter;
-use std::marker::PhantomData;
+#![no_std]
+
+#[macro_use]
+extern crate alloc;
+
+use alloc::string::String;
+use alloc::vec::Vec;
+use core::convert::TryInto;
+use core::fmt;
+use core::iter;
+use core::marker::PhantomData;
 
 use group::ff::{Field, FromUniformBytes, PrimeField};
 

halo2_poseidon/src/mds.rs

@@ -1,3 +1,5 @@
+use alloc::vec::Vec;
+
 use ff::FromUniformBytes;
 
 use super::{grain::Grain, Mds};

halo2_poseidon/src/p128pow5t3.rs

@@ -1,3 +1,5 @@
+use alloc::vec::Vec;
+
 use ff::Field;
 use pasta_curves::{pallas::Base as Fp, vesta::Base as Fq};
 
@@ -66,8 +68,10 @@ impl Spec<Fq, 3, 2> for P128Pow5T3 {
 
 #[cfg(test)]
 mod tests {
+    use alloc::vec::Vec;
+    use core::marker::PhantomData;
+
     use ff::{Field, FromUniformBytes, PrimeField};
-    use std::marker::PhantomData;
 
     use super::{
         super::{fp, fq},

halo2_poseidon/src/test_vectors.rs

@@ -1,5 +1,7 @@
 //! Test vectors for [`OrchardNullifier`].
 
+use alloc::vec::Vec;
+
 pub struct PermuteTestVector {
     pub initial_state: [[u8; 32]; 3],
     pub final_state: [[u8; 32]; 3],