Fix for bug #2664460: Various SeekableReadStream::seek() implementations (as well as our unit tests, ouch) handled SEEK_END incorrectly (using -offset instead of offset), contrary to what the docs said and what fseek does. Hopefully I found and fixed all affected parts, but still watch out for regressions

svn-id: r39135

backends/platform/ds/arm9/source/ramsave.cpp

@@ -205,7 +205,7 @@ bool DSSaveFile::seek(int32 pos, int whence) {
 			break;
 		}
 		case SEEK_END: {
-			ptr = save.size - pos;
+			ptr = save.size + pos;
 			break;
 		}
 	}

common/stream.cpp

@@ -69,7 +69,7 @@ bool MemoryReadStream::seek(int32 offs, int whence) {
 	case SEEK_END:
 		// SEEK_END works just like SEEK_SET, only 'reversed',
 		// i.e. from the end.
-		offs = _size - offs;
+		offs = _size + offs;
 		// Fall through
 	case SEEK_SET:
 		_ptr = _ptrOrig + offs;
@@ -204,7 +204,7 @@ bool SeekableSubReadStream::seek(int32 offset, int whence) {
 
 	switch(whence) {
 	case SEEK_END:
-		offset = size() - offset;
+		offset = size() + offset;
 		// fallthrough
 	case SEEK_SET:
 		_pos = _begin + offset;

engines/gob/inter_v1.cpp

@@ -2222,7 +2222,7 @@ bool Inter_v1::o1_readData(OpFuncParams &params) {
 
 		_vm->_draw->animateCursor(4);
 		if (offset < 0)
-			stream->seek(-offset - 1, SEEK_END);
+			stream->seek(offset + 1, SEEK_END);
 		else
 			stream->seek(offset);
 

engines/gob/inter_v2.cpp

@@ -1979,7 +1979,7 @@ bool Inter_v2::o2_readData(OpFuncParams &params) {
 
 	_vm->_draw->animateCursor(4);
 	if (offset < 0)
-		stream->seek(-offset - 1, SEEK_END);
+		stream->seek(offset + 1, SEEK_END);
 	else
 		stream->seek(offset);
 

engines/parallaction/disk_ns.cpp

@@ -661,7 +661,7 @@ public:
 			return;
 		}
 
-		stream.seek(4, SEEK_END);
+		stream.seek(-4, SEEK_END);
 		uint32 decrlen = stream.readUint32BE() >> 8;
 		byte *dest = (byte*)malloc(decrlen);
 

engines/scumm/file.cpp

@@ -142,7 +142,7 @@ bool ScummFile::seek(int32 offs, int whence) {
 		// Constrain the seek to the subfile
 		switch (whence) {
 		case SEEK_END:
-			offs = _subFileStart + _subFileLen - offs;
+			offs = _subFileStart + _subFileLen + offs;
 			break;
 		case SEEK_SET:
 			offs += _subFileStart;

test/common/bufferedseekablereadstream.h

@@ -56,13 +56,13 @@ class BufferedSeekableReadStreamTestSuite : public CxxTest::TestSuite {
 		b = ssrs.readByte();
 		TS_ASSERT( ssrs.eos() );
 
-		ssrs.seek(3, SEEK_END);
+		ssrs.seek(-3, SEEK_END);
 		TS_ASSERT( !ssrs.eos() );
 		TS_ASSERT_EQUALS( ssrs.pos(), 7 );
 		b = ssrs.readByte();
 		TS_ASSERT_EQUALS( b, 7 );
 
-		ssrs.seek(8, SEEK_END);
+		ssrs.seek(-8, SEEK_END);
 		TS_ASSERT_EQUALS( ssrs.pos(), 2 );
 		b = ssrs.readByte();
 		TS_ASSERT_EQUALS( b, 2 );

test/common/memoryreadstream.h

@@ -0,0 +1,61 @@
+#include <cxxtest/TestSuite.h>
+
+#include "common/stream.h"
+
+class MemoryReadStreamTestSuite : public CxxTest::TestSuite {
+	public:
+	void test_seek_set(void) {
+		byte contents[] = { 'a', 'b', '\n', '\n', 'c', '\n' };
+		Common::MemoryReadStream ms(contents, sizeof(contents));
+
+		ms.seek(0, SEEK_SET);
+		TS_ASSERT_EQUALS(ms.pos(), 0);
+		TS_ASSERT(!ms.eos());
+
+		ms.seek(1, SEEK_SET);
+		TS_ASSERT_EQUALS(ms.pos(), 1);
+		TS_ASSERT(!ms.eos());
+
+		ms.seek(5, SEEK_SET);
+		TS_ASSERT_EQUALS(ms.pos(), 5);
+		TS_ASSERT(!ms.eos());
+	}
+
+	void test_seek_cur(void) {
+		byte contents[] = { 'a', 'b', '\n', '\n', 'c' };
+		Common::MemoryReadStream ms(contents, sizeof(contents));
+
+		ms.seek(3, SEEK_CUR);
+		TS_ASSERT_EQUALS(ms.pos(), 3);
+		TS_ASSERT(!ms.eos());
+
+		ms.seek(-1, SEEK_CUR);
+		TS_ASSERT_EQUALS(ms.pos(), 2);
+		TS_ASSERT(!ms.eos());
+
+		ms.seek(3, SEEK_CUR);
+		TS_ASSERT_EQUALS(ms.pos(), 5);
+		TS_ASSERT(!ms.eos());
+
+		ms.seek(-1, SEEK_CUR);
+		TS_ASSERT_EQUALS(ms.pos(), 4);
+		TS_ASSERT(!ms.eos());
+	}
+
+	void test_seek_end(void) {
+		byte contents[] = { 'a', 'b', '\n', '\n', 'c' };
+		Common::MemoryReadStream ms(contents, sizeof(contents));
+
+		ms.seek(0, SEEK_END);
+		TS_ASSERT_EQUALS(ms.pos(), 5);
+		TS_ASSERT(!ms.eos());
+
+		ms.seek(-1, SEEK_END);
+		TS_ASSERT_EQUALS(ms.pos(), 4);
+		TS_ASSERT(!ms.eos());
+
+		ms.seek(-5, SEEK_END);
+		TS_ASSERT_EQUALS(ms.pos(), 0);
+		TS_ASSERT(!ms.eos());
+	}
+};

test/common/seekablesubreadstream.h

@@ -58,13 +58,13 @@ class SeekableSubReadStreamTestSuite : public CxxTest::TestSuite {
 		b = ssrs.readByte();
 		TS_ASSERT( ssrs.eos() );
 
-		ssrs.seek(3, SEEK_END);
+		ssrs.seek(-3, SEEK_END);
 		TS_ASSERT( !ssrs.eos() );
 		TS_ASSERT_EQUALS( ssrs.pos(), 5 );
 		b = ssrs.readByte();
 		TS_ASSERT_EQUALS( b, 6 );
 
-		ssrs.seek(8, SEEK_END);
+		ssrs.seek(-8, SEEK_END);
 		TS_ASSERT_EQUALS( ssrs.pos(), 0 );
 		b = ssrs.readByte();
 		TS_ASSERT_EQUALS( b, 1 );