I was having trouble using unordered_map<> with the gcc 4.6.1 tool chain targeting x86 and linking against "GNU with 
exceptions". The release build would hang when unordered_map<> constructor was called, but not hang in the debug build. 
Debugging the release build shows it gets stuck in ceilf().

After looking over gcc source I see that unordered_map<> is fairly different between release and debug, so debug 
apparently doesn't call ceilf(). The release version actually calls __builtin_ceil() in hashtable_policy.h.

So I decided to call ceilf() myself and sure enough, it hangs in debug and release builds. Then I tried gcc 4.4.2 and it
 also hangs.

Appears that C ceilf() calls C++ 'float ceil( float )', which calls C ceilf() again...hence an infinite loop.

I downloaded and tried the exact same code in MinGW with gcc 4.6.1 and it works fine.

I'm getting by with using map<> instead, but I would like to use unordered_map<> if there is a fix.