B.2.24 -fns[={no|yes}]

• (SPARC) Turns on the SPARC nonstandard floating-point mode.

  The default is -fns=no, the SPARC standard floating-point mode. -fns is the same as -fns=yes.

  Optional use of =yes or =no provides a way of toggling the -fns flag following some other macro flag that includes -fns, such as -fast.

  On some SPARC systems, the nonstandard floating point mode disables “gradual underflow,” causing tiny results to be flushed to zero rather than producing subnormal numbers. It also causes subnormal operands to be replaced silently by zero. On those SPARC systems that do not support gradual underflow and subnormal numbers in hardware, use of this option can significantly improve the performance of some programs.

  When nonstandard mode is enabled, floating point arithmetic may produce results that do not conform to the requirements of the IEEE 754 standard. See the Numerical Computation Guide for more information.

  This option is effective only on SPARC systems and only if used when compiling the main program. On x86 systems, the option is ignored.

• (x86) Selects SSE flush-to-zero mode and, where available, denormals-are-zero mode.

  This option causes subnormal results to be flushed to zero. Where available, this option also causes subnormal operands to be treated as zero.

  This option has no effect on traditional x86 floating-point operations that donot utilize the SSE or SSE2 instruction set.