Hello. I'm not on the list, so please CC me with any replies.
I have come across a bug found during some code which serializes
doubles. The bug is only encountered when the optimization level is set
to -O2 or greater.
The bug is not encountered when compiled under
gcc (GCC) 3.3.3 20040412 (Red Hat Linux 3.3.3-7)
at any optimization level.
The de-serialization code is:
typedef unsigned char uint8;
static uint8 next_byte(uint &offset, std::vector<uint8> const &bytecode)
throw (std::invalid_argument)
{
if (offset >= bytecode.size())
throw (std::invalid_argument("Unexpected end of bytecode"));
return bytecode[offset++];
}
double parse_double(uint &offset, std::vector<unsigned char> const &bytecode)
throw (std::invalid_argument)
{
typedef unsigned long long uint64;
uint64 rtn = uint64(next_byte(offset, bytecode)) << 56;
rtn |= uint64(next_byte(offset, bytecode)) << 48;
rtn |= uint64(next_byte(offset, bytecode)) << 40;
rtn |= uint64(next_byte(offset, bytecode)) << 32;
rtn |= uint64(next_byte(offset, bytecode)) << 24;
rtn |= uint64(next_byte(offset, bytecode)) << 16;
rtn |= uint64(next_byte(offset, bytecode)) << 8;
rtn |= uint64(next_byte(offset, bytecode));
return *reinterpret_cast<double*>(&rtn);
}
Full source code to a demonstration of the bug, and a Makefile is at
http://mjfrazer.org/~mjfrazer/tmp/pack-test/
The tar file in the directory contains all the other files, so you just
need to grab that.
cheers
-mark
