Purpose
Specifies the rounding mode for the compiler
to use when evaluating constant floating-point expressions at compile
time.
Syntax

.-n-.
>>- -y--+-m-+--------------------------------------------------><
+-p-+
'-z-'
Parameters
The following suboptions are valid for binary
floating-point types only:
- m
- Round toward minus infinity.
- n
- Round to the nearest representable number, ties to even.
- p
- Round toward plus infinity.
- z
- Round toward zero.
Usage
If your program contains operations involving long doubles, the rounding
mode must be set to -yn (round-to-nearest
representable number, ties to even).
Examples
To compile
myprogram.c so that constant floating-point expressions
are rounded toward zero at compile time, enter:
xlc myprogram.c -yz