C library for bitmessage PoW

Originally from https://github.com/bm-robertwhite/bitmessage-powfaster.
Modified to compile correctly on Visual Studio, and to decrease thread
priority.
I have not tried it on Linux yet.

src/bitmsghash.cpp

@@ -0,0 +1,89 @@
+// bitmessage cracker, build with g++ or MSVS to a shared library, use included python code for usage under bitmessage
+#ifdef _WIN32
+#include "Winsock.h"
+#include "Windows.h"
+#define uint64_t unsigned __int64
+#else
+#include <arpa/inet.h>
+#include <pthread.h>
+#include <stdint.h>
+#endif
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "openssl/sha.h"
+
+#define HASH_SIZE 64
+#define BUFLEN 16384
+
+#define ntohll(x) ( ( (uint64_t)(ntohl( (unsigned int)((x << 32) >> 32) )) << 32) | ntohl( ((unsigned int)(x >> 32)) ) )
+
+unsigned long long max_val;
+unsigned char *initialHash;
+
+
+int numthreads = 8;
+unsigned long long successval = 0;
+#ifdef _WIN32
+DWORD WINAPI threadfunc(LPVOID lpParameter) {
+	DWORD incamt = (DWORD)lpParameter;
+#else
+void * threadfunc(void* param) {
+	unsigned int incamt = (unsigned int)param;
+#endif
+	SHA512_CTX sha;
+	unsigned char buf[HASH_SIZE + sizeof(uint64_t)] = { 0 };
+	unsigned char output[HASH_SIZE] = { 0 };
+
+	memcpy(buf + sizeof(uint64_t), initialHash, HASH_SIZE);
+
+	unsigned long long tmpnonce = incamt;
+	unsigned long long * nonce = (unsigned long long *)buf;
+	unsigned long long * hash = (unsigned long long *)output;
+	while (successval == 0) {
+		tmpnonce += numthreads;
+
+		(*nonce) = ntohll(tmpnonce); /* increment nonce */
+		SHA512_Init(&sha);
+		SHA512_Update(&sha, buf, HASH_SIZE + sizeof(uint64_t));
+		SHA512_Final(output, &sha);
+		SHA512_Init(&sha);
+		SHA512_Update(&sha, output, HASH_SIZE);
+		SHA512_Final(output, &sha);
+
+		if (ntohll(*hash) < max_val) {
+			successval = tmpnonce;
+		}
+	}
+	return NULL;
+}
+
+extern "C" __declspec(dllexport) unsigned long long BitmessagePOW(unsigned char * starthash, unsigned long long target)
+{
+	successval = 0;
+	max_val = target;
+	initialHash = (unsigned char *)starthash;
+#   ifdef _WIN32
+	HANDLE* threads = (HANDLE*)calloc(sizeof(HANDLE), numthreads);
+#   else
+	pthread_t* threads = calloc(sizeof(pthread_t), numthreads);
+#   endif
+	for (int i = 0; i < numthreads; i++) {
+#   ifdef _WIN32
+		threads[i] = CreateThread(NULL, 0, threadfunc, (LPVOID)i, 0, NULL);
+		SetThreadPriority(threads[i], THREAD_PRIORITY_IDLE);
+#   else
+		pthread_create(&threads[i], NULL, threadfunc, (void*)i);
+#   endif
+	}
+#   ifdef _WIN32
+	WaitForMultipleObjects(numthreads, threads, TRUE, INFINITE);
+#   else
+	for (int i = 0; i < numthreads; i++) {
+		pthread_join(threads[i], NULL);
+	}
+#   endif
+	free(threads);
+	return successval;
+}