Expose API for init/free of parameters and, to test, a merkle tree hash invocation.

include/librustzcash.h

@@ -3,8 +3,42 @@
 
 #include <stdint.h>
 
+struct librustzcash_params {
+};
+
 extern "C" {
     uint64_t librustzcash_xor(uint64_t a, uint64_t b);
+
+    /// Initializes some parameters for sapling-crypto,
+    /// returning a pointer to the parameters. You should
+    /// free this when you're done with 
+    /// `librustzcash_init_params()`.
+    librustzcash_params* librustzcash_init_params();
+
+    /// 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,
+        unsigned char *result
+    );
 }
 
 #endif // LIBRUSTZCASH_INCLUDE_H_