Add poseidon-rs Fr from string & hex examples

poseidon-rs-examples/.gitignore

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+/target
+Cargo.lock

poseidon-rs-examples/Cargo.toml

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+[package]
+name = "poseidon-rs-examples"
+version = "0.0.1"
+authors = ["arnaucube <root@arnaucube.com>"]
+edition = "2018"
+
+[dependencies]
+ff = {package="ff_ce" , version="0.11", features = ["derive"]}
+poseidon-rs = "0.0.4"
+rustc-hex = "1.0.0"
+num = "0.2.0"
+num-bigint = "0.2.2"

poseidon-rs-examples/src/lib.rs

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+#[cfg(test)]
+mod tests {
+    use ff::PrimeField;
+    use poseidon_rs::{Fr, Poseidon};
+
+    // for parsing hex
+    extern crate num;
+    extern crate num_bigint;
+    use num_bigint::BigInt;
+
+    #[test]
+    fn test_usage() {
+        let v: Fr = Fr::from_str(
+            "11043376183861534927536506085090418075369306574649619885724436265926427398571",
+        )
+        .unwrap();
+        let mut to_hash: Vec<Fr> = Vec::new();
+        to_hash.push(v);
+
+        let poseidon = Poseidon::new();
+        let h = poseidon.hash(to_hash).unwrap();
+        assert_eq!(
+            h.to_string(),
+            "Fr(0x28410c403c92a9f18d1f27b22218b3649b3be8640dc160ad53bd21cf02f98d81)"
+        );
+    }
+
+    #[test]
+    fn test_usage_hex() {
+        let b: BigInt = BigInt::parse_bytes(
+            b"186a5454a7c47c73dfc74ac32ea40a57d27eeb4e2bfc6551dd7b66686d3fd1ab", // same value than in previous test, but in hex
+            16,
+        )
+        .unwrap();
+
+        let v: Fr = Fr::from_str(&b.to_string()).unwrap();
+        let mut to_hash: Vec<Fr> = Vec::new();
+        to_hash.push(v);
+
+        let poseidon = Poseidon::new();
+        let h = poseidon.hash(to_hash).unwrap();
+        assert_eq!(
+            h.to_string(),
+            "Fr(0x28410c403c92a9f18d1f27b22218b3649b3be8640dc160ad53bd21cf02f98d81)"
+        );
+    }
+}