Even though I may encounter more bugs in the latter situation, I feel less pain when I encounter them. And I have the satisfaction that I'm somehow making the world a better place.
But the point remains that relying on any specific floating point semantics (in C, or any other language) is dangerous.
The potentially infinite loop in strtod was a bug, no matter how you spin it to blame the compiler. Iterative algorithms that must finish in limited time must always have a max # of iterations...
While there may be millions of servers running PHP, I doubt millions of users (PHP programmers) were the ones upgrading them. I'd be shocked, if _most_ PHP programmers have ever installed PHP themselves.
Installing: > apt-get install php5-xxx
Upgrading: > apt-get upgrade
Now, boohoo, that's so much work those users are forced to do...
He has a point about this code being used everywhere though. When we figured out what caused this we did a quick search to see how other people who use this same code deals with this issue. And for the most part they don't. The version in Spidermonkey, for example, is a newer version, but very similar. Dropping the Spidermonkey version into PHP produces the same problem. The one saving factor here is that 32-bit x87 hardware is going away pretty quickly, so this particular annoyance is getting less and less important.
The C standard allows compilers to keep floating-point intermediate results in registers; this is both faster, and can give more accurate results. Since it is allowed, GCC does so when IEEE-extended mode is enabled by compiler flags. PHP enabled those flags, so GCC enables IEEE-extended math, and thus keeps results in registers.
There are a couple ways the PHP developers can fix this:
1. Since the code explicitly says it does not work in IEEE-extended mode, they can disable it by adding "-fexcess-precision=standard" (for GCC) or "-fp-model precise" (for ICC) to their CFLAGS.
2. Alternatively, they could compile in C99 mode; C99 changed the floating-point semantics to make IEEE mode the default.
3. They could use the system's strtod() or strtod_l() , which is presumably designed to work on the current architecture.
Finally, regarding the author's suggestion to use Clang: the only reason Clang works as he expects (eg, incorrectly) is because it apparently does not support IEEE-extended math on x87-enabled processors. Suggesting that users switch to a compiler because it is missing features is ridiculous, especially if they add support for this feature later.
I see Miguel finally caved!
