Use lazy_static to initialize the Jubjub parameters, to avoid passing parameters around.

Cargo.lock

@@ -100,6 +100,11 @@ dependencies = [
  "typenum 1.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "lazy_static"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "libc"
 version = "0.2.40"
@@ -109,6 +114,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "librustzcash"
 version = "0.1.0"
 dependencies = [
+ "lazy_static 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.40 (registry+https://github.com/rust-lang/crates.io-index)",
  "pairing 0.14.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "sapling-crypto 0.0.1 (git+https://github.com/zcash-hackworks/sapling-crypto?rev=e554b473dd10885d232f42237c13282f5b6fee43)",
@@ -198,6 +204,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum futures 0.1.21 (registry+https://github.com/rust-lang/crates.io-index)" = "1a70b146671de62ec8c8ed572219ca5d594d9b06c0b364d5e67b722fc559b48c"
 "checksum futures-cpupool 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)" = "ab90cde24b3319636588d0c35fe03b1333857621051837ed769faefb4c2162e4"
 "checksum generic-array 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ef25c5683767570c2bbd7deba372926a55eaae9982d7726ee2a1050239d45b9d"
+"checksum lazy_static 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "c8f31047daa365f19be14b47c29df4f7c3b581832407daabe6ae77397619237d"
 "checksum libc 0.2.40 (registry+https://github.com/rust-lang/crates.io-index)" = "6fd41f331ac7c5b8ac259b8bf82c75c0fb2e469bbf37d2becbba9a6a2221965b"
 "checksum nodrop 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)" = "9a2228dca57108069a5262f2ed8bd2e82496d2e074a06d1ccc7ce1687b6ae0a2"
 "checksum num_cpus 1.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "c51a3322e4bca9d212ad9a158a02abc6934d005490c054a2778df73a70aa0a30"

Cargo.toml

@@ -11,6 +11,7 @@ crate-type = ["staticlib"]
 [dependencies]
 libc = "0.2"
 pairing = "0.14.1"
+lazy_static = "1"
 
 [dependencies.sapling-crypto]
 git = "https://github.com/zcash-hackworks/sapling-crypto"

include/librustzcash.h

@@ -3,37 +3,26 @@
 
 #include <stdint.h>
 
-struct librustzcash_params {
-};
-
 extern "C" {
     uint64_t librustzcash_xor(uint64_t a, uint64_t b);
 
-    /// Initializes some parameters for sapling-crypto,
+    /// Writes the "uncommitted" note value for empty leaves
-    /// returning a pointer to the parameters. You should
+    /// of the merkle tree. `result` must be a valid pointer
-    /// free this when you're done with 
+    /// to 32 bytes which will be written.
-    /// `librustzcash_free_params()`.
+    void librustzcash_tree_uncommitted(
-    librustzcash_params* librustzcash_init_params();
+        unsigned char *result
-
+    );
-    /// Frees some parameters that were previously returned
-    /// from `librustzcash_init_params()`. Only call this
-    /// once.
-    void librustzcash_free_params(librustzcash_params* params);
 
     /// Computes a merkle tree hash for a given depth.
     /// The `depth` parameter should not be larger than
     /// 62.
     ///
-    /// Params must be a valid pointer that was returned
-    /// from `librustzcash_init_params()`.
-    ///
     /// `a` and `b` each must be of length 32, and must each
     /// be scalars of BLS12-381.
     ///
     /// The result of the merkle tree hash is placed in
     /// `result`, which must also be of length 32.
     void librustzcash_merkle_hash(
-        const librustzcash_params* params,
         size_t depth,
         const unsigned char *a,
         const unsigned char *b,

src/rustzcash.rs

@@ -2,6 +2,9 @@ extern crate libc;
 extern crate sapling_crypto;
 extern crate pairing;
 
+#[macro_use]
+extern crate lazy_static;
+
 use pairing::{
     BitIterator,
     PrimeFieldRepr,
@@ -23,40 +26,34 @@ use sapling_crypto::{
 
 use libc::{uint64_t, size_t, c_uchar};
 
-pub struct SaplingParams {
+lazy_static! {
-    pub jubjub_params: JubjubBls12
+    static ref JUBJUB: JubjubBls12 = {
-}
+        JubjubBls12::new()
-
+    };
-#[no_mangle]
-pub extern "system" fn librustzcash_init_params() -> *mut SaplingParams {
-    Box::into_raw(Box::new(SaplingParams{
-        jubjub_params: JubjubBls12::new()
-    }))
 }
 
 #[no_mangle]
-pub extern "system" fn librustzcash_free_params(
+pub extern "system" fn librustzcash_tree_uncommitted(
-    params: *mut SaplingParams
+    result: *mut [c_uchar; 32]
 )
 {
-    let tmp = unsafe { Box::from_raw(params) };
+    let tmp = sapling_crypto::primitives::Note::<Bls12>::uncommitted().into_repr();
+
+    // Should be okay, caller is responsible for ensuring the pointer
+    // is a valid pointer to 32 bytes that can be mutated.
+    let result = unsafe { &mut *result };
 
-    drop(tmp);
+    tmp.write_be(&mut result[..]).unwrap();
 }
 
 #[no_mangle]
 pub extern "system" fn librustzcash_merkle_hash(
-    params: *const SaplingParams,
     depth: size_t,
     a: *const [c_uchar; 32],
     b: *const [c_uchar; 32],
     result: *mut [c_uchar; 32],
 )
 {
-    // Should be okay, because caller is responsible for ensuring
-    // params points to valid parameters.
-    let params = unsafe { &*params };
-
     let mut a_repr = FrRepr::default();
     let mut b_repr = FrRepr::default();
 
@@ -86,7 +83,7 @@ pub extern "system" fn librustzcash_merkle_hash(
         lhs.iter().map(|&x| x)
             .take(Fr::NUM_BITS as usize)
             .chain(rhs.iter().map(|&x| x).take(Fr::NUM_BITS as usize)),
-        &params.jubjub_params
+        &JUBJUB
     ).into_xy().0.into_repr();
 
     // Should be okay, caller is responsible for ensuring the pointer