From 9f795150fc622033a24bc88db24aa99dfa13fdfa Mon Sep 17 00:00:00 2001
From: OV2 <OV2@sessionclan.de>
Date: Tue, 6 Nov 2018 22:05:38 +0100
Subject: [PATCH] Correct stream revert behavior (closes #353)

---
 stream.cpp | 35 +++++++++++++++++++++++++++--------
 stream.h   | 13 ++++++++-----
 2 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/stream.cpp b/stream.cpp
index b385e51a..c8e8af6e 100644
--- a/stream.cpp
+++ b/stream.cpp
@@ -253,6 +253,24 @@ std::string Stream::getline (bool &eof)
 	return (ret);
 }
 
+size_t Stream::pos_from_origin_offset(uint8 origin, int32 offset)
+{
+    size_t position = 0;
+    switch (origin)
+    {
+        case SEEK_SET:
+            position = offset;
+            break;
+        case SEEK_END:
+            position = size() + offset;
+            break;
+        case SEEK_CUR:
+            position = pos() + offset;
+            break;
+    }
+    return position;
+}
+
 // snes9x.h FSTREAM Stream
 
 fStream::fStream (FSTREAM f)
@@ -299,9 +317,9 @@ size_t fStream::size (void)
     return sz;
 }
 
-int fStream::revert (size_t from, size_t offset)
+int fStream::revert (uint8 origin, int32 offset)
 {
-    return (REVERT_FSTREAM(fp, offset, from));
+    return (REVERT_FSTREAM(fp, offset, origin));
 }
 
 void fStream::closeStream()
@@ -428,9 +446,9 @@ size_t unzStream::size (void)
     return info.uncompressed_size;
 }
 
-int unzStream::revert (size_t from, size_t offset)
+int unzStream::revert (uint8 origin, int32 offset)
 {
-    size_t target_pos = from + offset;
+    size_t target_pos = pos_from_origin_offset(origin, offset);
 
     // new pos inside buffered data
     if (target_pos >= buf_pos_in_unzipped && target_pos < buf_pos_in_unzipped + bytes_in_buf)
@@ -547,9 +565,9 @@ size_t memStream::size (void)
     return msize;
 }
 
-int memStream::revert (size_t from, size_t offset)
+int memStream::revert (uint8 origin, int32 offset)
 {
-    size_t pos = from + offset;
+    size_t pos = pos_from_origin_offset(origin, offset);
 
     if(pos > msize)
         return -1;
@@ -610,9 +628,10 @@ size_t nulStream::size (void)
     return bytes_written;
 }
 
-int nulStream::revert (size_t from, size_t offset)
+int nulStream::revert (uint8 origin, int32 offset)
 {
-    bytes_written = from + offset;
+    size_t target_pos = pos_from_origin_offset(origin, offset);
+    bytes_written = target_pos;
     return 0;
 }
 
diff --git a/stream.h b/stream.h
index 16ceee5a..c62da9c4 100644
--- a/stream.h
+++ b/stream.h
@@ -208,8 +208,11 @@ class Stream
         virtual size_t write (void *, size_t) = 0;
         virtual size_t pos (void) = 0;
         virtual size_t size (void) = 0;
-        virtual int revert (size_t from, size_t offset) = 0;
+        virtual int revert (uint8 origin, int32 offset) = 0;
         virtual void closeStream() = 0;
+
+	protected:
+		size_t pos_from_origin_offset(uint8 origin, int32 offset);
 };
 
 class fStream : public Stream
@@ -223,7 +226,7 @@ class fStream : public Stream
         virtual size_t write (void *, size_t);
         virtual size_t pos (void);
         virtual size_t size (void);
-        virtual int revert (size_t from, size_t offset);
+        virtual int revert (uint8 origin, int32 offset);
         virtual void closeStream();
 
 	private:
@@ -250,7 +253,7 @@ class unzStream : public Stream
         virtual size_t write (void *, size_t);
         virtual size_t pos (void);
         virtual size_t size (void);
-        virtual int revert (size_t from, size_t offset);
+        virtual int revert (uint8 origin, int32 offset);
         virtual void closeStream();
 
 	private:
@@ -279,7 +282,7 @@ class memStream : public Stream
         virtual size_t write (void *, size_t);
         virtual size_t pos (void);
         virtual size_t size (void);
-        virtual int revert (size_t from, size_t offset);
+        virtual int revert (uint8 origin, int32 offset);
         virtual void closeStream();
 
 	private:
@@ -304,7 +307,7 @@ class nulStream : public Stream
         virtual size_t write (void *, size_t);
         virtual size_t pos (void);
         virtual size_t size (void);
-        virtual int revert (size_t from, size_t offset);
+        virtual int revert (uint8 origin, int32 offset);
         virtual void closeStream();
 
     private: