1 files changed, 118 insertions, 0 deletions
diff --git a/Source/Internal/checksum.cpp b/Source/Internal/checksum.cpp
new file mode 100644
index 00000000..2e74a378
--- /dev/null
+++ b/Source/Internal/checksum.cpp
@@ -0,0 +1,118 @@
+//-----------------------------------------------------------------------------
+//           Name: checksum.cpp
+//      Developer: Wolfire Games LLC
+//    Description:
+//        License: Read below
+//-----------------------------------------------------------------------------
+//
+//   Copyright 2022 Wolfire Games LLC
+//
+//   Licensed under the Apache License, Version 2.0 (the "License");
+//   you may not use this file except in compliance with the License.
+//   You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+//   Unless required by applicable law or agreed to in writing, software
+//   distributed under the License is distributed on an "AS IS" BASIS,
+//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//   See the License for the specific language governing permissions and
+//   limitations under the License.
+//
+//-----------------------------------------------------------------------------
+#include "checksum.h"
+
+#include <Internal/error.h>
+#include <Internal/profiler.h>
+#include <Internal/common.h>
+
+#include <Compat/fileio.h>
+#include <Memory/allocation.h>
+
+#include <stdio.h>
+#include <string>
+
+using std::string;
+using std::endl;
+
+class ProfilerContext;
+
+//TODO: Maybe modifying this to be Adler32 would be a little better CRC32 even more so, lowering the risk for collisions for small changes. 
+//(If you make a 'b' a 'c' and another 'b' an 'a' in a file, this function will give you the same checksum value, i would consider this a possible common change)
+unsigned short Checksum(const string& abs_path) {
+    PROFILER_ZONE(g_profiler_ctx, "Checksum");
+    unsigned short sum = 0;
+
+    FILE * pFile;
+    long lSize;
+    unsigned char * buffer;
+    size_t result;
+
+    pFile = my_fopen ( abs_path.c_str() , "rb" );
+
+#ifndef NO_ERR
+    const int kBufSize = 512;
+    char error_msg[kBufSize];
+    while (pFile==NULL) {
+        FormatString(error_msg, kBufSize, "Could not open file: %s. Retry?", abs_path.c_str());
+        DisplayError("Error", error_msg, _ok_cancel);
+        pFile = my_fopen ( abs_path.c_str() , "rb" );
+    }
+#endif
+
+    if( pFile ) {
+        // obtain file size:
+        fseek (pFile , 0 , SEEK_END);
+        lSize = ftell (pFile);
+        rewind (pFile);
+
+        // allocate memory to contain the whole file:
+        buffer = (unsigned char*) alloc.stack.Alloc(sizeof(char)*lSize);
+
+        if( buffer ) {
+        #ifndef NO_ERR
+            if (buffer == NULL) {
+                FormatString(error_msg, kBufSize, "Could not allocate memory to checksum: %s.", abs_path.c_str());
+                FatalError("Error", error_msg);
+            }
+        #endif
+
+            // copy the file into the buffer:
+            result = fread (buffer,1,lSize,pFile);
+        #ifndef NO_ERR
+            if (result != (size_t)lSize) {
+                FormatString(error_msg, kBufSize, "Could not read data from file: %s.", abs_path.c_str());
+                FatalError("Error", error_msg);
+            }
+        #endif
+
+            {
+                PROFILER_ZONE(g_profiler_ctx, "Actual summation");
+                size_t short_count = lSize/2;
+                for (size_t i = 0; i < short_count; i++){
+                    // Might have trouble on wrong-endian machines, but those should probably just have different checksums built in anyhow, to keep this fast
+                    sum += ((uint16_t*)buffer)[i];
+                }
+            }
+            alloc.stack.Free(buffer);
+        } else {
+            LOGE << "Failed to allocate data from stack allocator, size: " << lSize << endl;
+        }
+        // terminate
+        fclose (pFile);
+    } else {
+        LOGE << "Failed to open file " << abs_path << endl;
+    }
+    return sum;
+}
+
+// From http://www.cse.yorku.ca/~oz/hash.html
+unsigned long djb2_string_hash(const char *cstr){
+    unsigned long hash = 5381;
+    int c;
+
+    while ((c = *cstr++))
+        hash = ((hash << 5) + hash) + c; /* hash * 33 + c */
+
+    return hash;
+}