PGI User Forum

[mkcolg]

Sounds like it might be more of an issue of the x87 80-bit double precision floating point representation rather than large file support. When using "-Kieee" and/or "-pc 64" your telling the compiler that you want the 64-bit representation. I believe SGI, HP, and Alpha all use the 64-bits.

What happens is the compiler will try and keep values in the 80-bit floating point registers since this makes for more efficiant code. However, this can lead to different answers since your using a more precise representation, especially for very small numbers. Once the value is stored into memory, then it is truncated to 64-bit.

Since your running on a P4, I would suggest using the SSE registers instead of the x87 registers since they use a 64-bit representation. (They are actually 128-bits but perform two 64-bit operations). To use SSE, specify the flag "-Mscalarsse" on the command line. You can then add additional optimizations, such as "-fast" or "-fastsse" which includes "-Mscalarsse" to help increase perfromance.

Hope this helps,
Mat

[sungchan]

So far, I have seen problems with 64 bit library. I got the same wrong answers when I compiled on Xeon workstation using -Mlfs option and when I compiled on Opteron workstation (/usr/pgi/linux-64/5.1 is the directory). Without any option switches, I got expected results (meaning similar to the results from alpha workstation and SGI workstation as well as Cray) on my Xeon workstation (I am using v.5.2).

I still like to use my Opteron workstation (or -Mlfs switch on my Xeon workstation) because sometimes I like to deal with file size > 2 GB. Can anyone think of the reason why I have these problems?