From 29ad41dd569c877b57ef29cebcc04eb24b3bb895 Mon Sep 17 00:00:00 2001
From: Mark Friedenbach <mark@friedenbach.org>
Date: Fri, 22 Jan 2016 08:19:17 -0800
Subject: [PATCH] Add mistate output to CSHA256.

This allows the intermediate state of a SHA-256 run to be saved for future resumption, or in the case of fast Merkle trees to perform a non-padded hash.
---
 src/crypto/sha256.cpp | 11 +++++++++++
 src/crypto/sha256.h   |  1 +
 2 files changed, 12 insertions(+)

diff --git a/src/crypto/sha256.cpp b/src/crypto/sha256.cpp
index 5b9f00a0a2..f76193daee 100644
--- a/src/crypto/sha256.cpp
+++ b/src/crypto/sha256.cpp
@@ -171,6 +171,11 @@ void CSHA256::Finalize(unsigned char hash[OUTPUT_SIZE])
     WriteBE64(sizedesc, bytes << 3);
     Write(pad, 1 + ((119 - (bytes % 64)) % 64));
     Write(sizedesc, 8);
+    Midstate(hash, NULL, NULL);
+}
+
+void CSHA256::Midstate(unsigned char hash[OUTPUT_SIZE], uint64_t* len, unsigned char *buffer)
+{
     WriteBE32(hash, s[0]);
     WriteBE32(hash + 4, s[1]);
     WriteBE32(hash + 8, s[2]);
@@ -179,6 +184,12 @@ void CSHA256::Finalize(unsigned char hash[OUTPUT_SIZE])
     WriteBE32(hash + 20, s[5]);
     WriteBE32(hash + 24, s[6]);
     WriteBE32(hash + 28, s[7]);
+    if (len) {
+        *len = bytes << 3;
+    }
+    if (buffer) {
+        memcpy(buffer, buf, bytes % 64);
+    }
 }
 
 CSHA256& CSHA256::Reset()
diff --git a/src/crypto/sha256.h b/src/crypto/sha256.h
index 127e62a228..d053a34eb1 100644
--- a/src/crypto/sha256.h
+++ b/src/crypto/sha256.h
@@ -22,6 +22,7 @@ public:
     CSHA256();
     CSHA256& Write(const unsigned char* data, size_t len);
     void Finalize(unsigned char hash[OUTPUT_SIZE]);
+    void Midstate(unsigned char hash[OUTPUT_SIZE], uint64_t* bytes, unsigned char *buffer);
     CSHA256& Reset();
 };