Avoid ftell() calls by pfSizedStream.

According to profiling, calls to `ftell()` when reading creatables is
the largest time sink when reading PRPs. On a trivial test with two
iterations of loading Garrison, the results are thus:

Before: 68.68s (34.34s avg)
After: 7.68s (3.84s avg)

core/Stream/pfSizedStream.cpp

@@ -18,7 +18,7 @@
 #include "Debug/plDebug.h"
 
 pfSizedStream::pfSizedStream(hsStream* S, uint32_t len)
-    : fBase(S), fLength(len)
+    : fBase(S), fLength(len), fPos()
 {
     if (S) {
         ver = S->getVer();
@@ -41,37 +41,43 @@ void pfSizedStream::seek(uint32_t pos)
     }
 
     fBase->seek(fBegin + pos);
+    fPos = std::min(pos, fLength);
 }
 
 void pfSizedStream::skip(int32_t count)
 {
-    if (pos() + count > fLength) { // pos() is the index in the sub-stream
+    if (fPos + count > fLength) { // fPos is the index in the sub-stream
         throw hsFileReadException(__FILE__, __LINE__,
                          ST::format("Seek out of range: {} bytes requested, {} available",
-                         count, (fLength - pos())).c_str());
+                         count, (fLength - fPos)).c_str());
     }
 
     fBase->skip(count);
+    fPos += count;
 }
 
 size_t pfSizedStream::read(size_t size, void* buf)
 {
-    if (pos() + size > fLength) { // pos() is the index in the sub-stream
+    if (fPos + size > fLength) { // fPos is the index in the sub-stream
         throw hsFileReadException(__FILE__, __LINE__,
                          ST::format("Read past end of sized stream: {} bytes requested, {} available",
-                         size, (fLength - pos())).c_str());
+                         size, (fLength - fPos)).c_str());
     }
 
-    return fBase->read(size, buf);
+    size_t nread = fBase->read(size, buf);
+    fPos += nread;
+    return nread;
 }
 
 size_t pfSizedStream::write(size_t size, const void* buf)
 {
-    if (pos() + size > fLength) { // pos() is the index in the sub-stream
+    if (fPos + size > fLength) { // fPos is the index in the sub-stream
         throw hsFileReadException(__FILE__, __LINE__,
                          ST::format("Write past end of sized stream: {} bytes requested, {} available",
-                         size, (fLength - pos())).c_str());
+                         size, (fLength - fPos)).c_str());
     }
 
-    return fBase->write(size, buf);
+    size_t nwrite = fBase->write(size, buf);
+    fPos += nwrite;
+    return nwrite;
 }

core/Stream/pfSizedStream.h

@@ -19,20 +19,21 @@
 
 #include "hsStream.h"
 
-class PLASMA_DLL pfSizedStream : public hsStream
+class PLASMA_DLL pfSizedStream HS_FINAL : public hsStream
 {
 private:
     hsStream* fBase;
     uint32_t fLength; //!< the length of the substream - not the end position of it!
     uint32_t fBegin;
+    uint32_t fPos;
 
 public:
     pfSizedStream(hsStream* S, uint32_t len);
     ~pfSizedStream() { } // Do NOT free fBase!!!
 
     uint32_t size() const HS_OVERRIDE { return fLength; }
-    uint32_t pos() const HS_OVERRIDE { return fBase->pos() - fBegin; }
-    bool eof() const HS_OVERRIDE { return fBase->eof() || pos() == fLength; }
+    uint32_t pos() const HS_OVERRIDE { return fPos; }
+    bool eof() const HS_OVERRIDE { return fPos == fLength || fBase->eof(); }
 
     void seek(uint32_t pos) HS_OVERRIDE;
     void skip(int32_t count) HS_OVERRIDE;