experimental: provide SHA-256 transform to libsecp

Author: furszy

src/crypto/sha256.cpp

@@ -435,7 +435,6 @@ void TransformD64(unsigned char* out, const unsigned char* in)
 
 } // namespace sha256
 
-typedef void (*TransformType)(uint32_t*, const unsigned char*, size_t);
 typedef void (*TransformD64Type)(unsigned char*, const unsigned char*);
 
 template<TransformType tr>
@@ -779,3 +778,8 @@ void SHA256D64(unsigned char* out, const unsigned char* in, size_t blocks)
         --blocks;
     }
 }
+
+TransformType GetSha256TransformFn()
+{
+    return Transform;
+}

src/crypto/sha256.h

@@ -9,6 +9,8 @@
 #include <cstdlib>
 #include <string>
 
+typedef void (*TransformType)(uint32_t*, const unsigned char*, size_t);
+
 /** A hasher class for SHA-256. */
 class CSHA256
 {
@@ -50,4 +52,7 @@ std::string SHA256AutoDetect(sha256_implementation::UseImplementation use_implem
  */
 void SHA256D64(unsigned char* output, const unsigned char* input, size_t blocks);
 
+/* TODO: Complete me */
+TransformType GetSha256TransformFn();
+
 #endif // BITCOIN_CRYPTO_SHA256_H

src/key.cpp

@@ -583,6 +583,7 @@ static void ECC_Start() {
         assert(ret);
     }
 
+    secp256k1_set_sha256_transform_callback(GetSha256TransformFn());
     secp256k1_context_sign = ctx;
 }