About the INTEL bug :
From : x86.org
"The bug relates to operations that convert floating point numbers into integer numbers. Floating point
numbers are stored inside of the microprocessor in an 80-bit format. Integer numbers are stored in two
different sizes. A short integer is stored in 16-bits, and a long integer is stored in 32-bits. It is often desirable
to store the 80-bit floating point numbers as integer numbers. Sometimes the converted number won't fit into
the smaller integer format. This is when the bug occurs.
The host software is supposed to be warned by the microprocessor when such a floating point conversion
error occurs; a specific error flag is supposed to be set in a floating point status register. If the
microprocessor fails to set this flag, it would not be in compliance with the IEEE Floating Point Standards
which mandate such behavior. For the Dan-0411 bug, the Pentium II and Pentium Pro processors fail to set
this error flag in many cases.
This bug appears to affect 231 + 247 different floating point numbers. That's approximately
140,739,635,839,000 different floating point numbers that result in the incorrect behavior. The Pentium,
Pentium with MMX Technology, and AMD K6 microprocessors do not appear to have this problem.
It might be interesting to note that a launch failure of the Ariane 5 rocket, which happened less than a minute
into the launch, was traced to behavior around an overflow condition (in this case, it was software, not
hardware, that was the problem). One of the computers on board had a floating point to integer conversion
that overflowed, but because the overflow was not handled by the software the computer did a dump of its
memory. Unfortunately, this memory dump was interpreted by the rocket as instructions to its rocket nozzles.
Result--boom! " |
