[Boost-users] [unordered_map]: Unexpected exception on value insertion

Subject: [Boost-users] [unordered_map]: Unexpected exception on value insertion
From: Johannes Brunen (jbrunen_at_[hidden])
Date: 2012-08-21 04:47:03

Hello,

My program is crashing (not handling an unexpected exception) on
inserting a value into a unorderd map of type:
unordered_map<osg::Pnt3f, std::size_t, Pnt3fHashT> with

struct Pnt3fHashT : public std::unary_function<osg::Pnt3f, std::size_t>
{
    std::size_t operator()(const osg::Pnt3f& pnt) const
    {
        std::size_t seed = 0;
        boost::hash_combine(seed, pnt[0]);
        boost::hash_combine(seed, pnt[1]);
        boost::hash_combine(seed, pnt[2]);

        return seed;
    }
};

Pnt3f is a common 3D float point.

The program is compiled with Microsoft Visual C++ 2008 9.0.30729.1SP
64Bit and Boost 1.48.0. 
The crash does only occur on 64Bit compilations.

After inspection, I found the crash to be happening in the function 

inline std::size_t float_hash_impl2(T v)

found in source hash_float_generic.hpp.

Since the code looks fine for me I investigated the generated assembler
code and found

std::size_t seed = static_cast<std::size_t>(v);
000007FEE8A4D3C0  xor         ecx,ecx 
000007FEE8A4D3C2  movss       xmm0,dword ptr [v] 
000007FEE8A4D3CB  comiss      xmm0,dword ptr [__real_at_5f000000
(7FEE8FB7A34h)] 
000007FEE8A4D3D2  jbe
boost::hash_detail::float_hash_impl2<float>+0D2h (7FEE8A4D3F2h) 
000007FEE8A4D3D4  subss       xmm0,dword ptr [__real_at_5f000000
(7FEE8FB7A34h)] 
000007FEE8A4D3DC  comiss      xmm0,dword ptr [__real_at_5f000000
(7FEE8FB7A34h)] 
000007FEE8A4D3E3  jae
boost::hash_detail::float_hash_impl2<float>+0D2h (7FEE8A4D3F2h) 
000007FEE8A4D3E5  mov         rax,8000000000000000h 
000007FEE8A4D3EF  add         rcx,rax 
000007FEE8A4D3F2  cvttss2si   rax,xmm0 
000007FEE8A4D3F7  add         rax,rcx 
000007FEE8A4D3FA  mov         qword ptr [seed],rax 

The crash happens at the 

000007FEE8A4D3F2  cvttss2si   rax,xmm0 

instruction since the value in xmm0 is larger than the maximum signed
32bit integer. 
In this case depending on the settings an floating-point invalid
exception is raised. It crashes since
my code is not prepared for this exception.

Now I have some questions:
1. Is it known that this mapping into the realm of 32Bit is happening
for the above cast operation?
2. Is this a compiler bug? The generated assembler code does not allow
'safe' casting into 64bit integer?
3. Any advice how I should handle this situation?

Best,
Johannes

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