chore: fix pedersen_compress_with_hash_index c_bind function

barretenberg/cpp/src/barretenberg/crypto/pedersen_commitment/c_bind.cpp

@@ -20,7 +20,7 @@ WASM_EXPORT void pedersen__compress(uint8_t const* inputs_buffer, uint8_t* outpu
     barretenberg::fr::serialize_to_buffer(r, output);
 }
 
-WASM_EXPORT void pedersen__compress_with_hash_index(uint8_t const* inputs_buffer, uint8_t* output, uint32_t hash_index)
+WASM_EXPORT void pedersen__compress_with_hash_index(uint8_t const* inputs_buffer, uint32_t hash_index, uint8_t* output)
 {
     std::vector<grumpkin::fq> to_compress;
     read(inputs_buffer, to_compress);

barretenberg/cpp/src/barretenberg/crypto/pedersen_commitment/c_bind.hpp

@@ -10,7 +10,7 @@ WASM_EXPORT void pedersen__compress_fields(uint8_t const* left, uint8_t const* r
 
 WASM_EXPORT void pedersen__compress(uint8_t const* inputs_buffer, uint8_t* output);
 
-WASM_EXPORT void pedersen__compress_with_hash_index(uint8_t const* inputs_buffer, uint8_t* output, uint32_t hash_index);
+WASM_EXPORT void pedersen__compress_with_hash_index(uint8_t const* inputs_buffer, uint32_t hash_index, uint8_t* output);
 WASM_EXPORT void pedersen__commit(uint8_t const* inputs_buffer, uint8_t* output);
 
 WASM_EXPORT void pedersen__buffer_to_field(uint8_t const* data, size_t length, uint8_t* r);

yarn-project/circuits.js/src/barretenberg/crypto/pedersen/pedersen.ts

@@ -41,10 +41,24 @@ export function pedersenHashInputs(wasm: IWasmModule, inputs: Buffer[]): Buffer
 export function pedersenHashWithHashIndex(wasm: IWasmModule, inputs: Buffer[], hashIndex: number): Buffer {
   // If not done already, precompute constants.
   wasm.call('pedersen__init');
-  const inputVectors = serializeBufferArrayToVector(inputs);
-  wasm.writeMemory(0, inputVectors);
-  wasm.call('pedersen__compress_with_hash_index', 0, 0, hashIndex);
-  return Buffer.from(wasm.getMemorySlice(0, 32));
+
+  // Allocate memory for the inputs. We can optimize this
+  // by checking the length and copying the data to the
+  // wasm scratch space if it is small enough.
+  const data = serializeBufferArrayToVector(inputs);
+  const inputPtr = wasm.call('bbmalloc', data.length);
+  wasm.writeMemory(inputPtr, data);
+
+  // Since the output is 32 bytes, instead of allocating memory
+  // we can simply use the scratch space.
+  const outputPtr = 0;
+
+  wasm.call('pedersen__compress_with_hash_index', inputPtr, hashIndex, outputPtr);
+  const hashOutput = wasm.getMemorySlice(0, 32);
+
+  wasm.call('bbfree', inputPtr);
+
+  return Buffer.from(hashOutput);
 }
 
 /**