Sun Studio 12: C User's Guide

B.2.24 -fprecision=p

(x86) -fprecision={single, double, extended}

Initializes the rounding-precision mode bits in the Floating-point Control Word to single (24 bits), double (53 bits), or extended (64 bits), respectively. The default floating-point rounding-precision mode is extended.

Note that on x86, only the precision, not exponent, range is affected by the setting of floating-point rounding precision mode.