HP Pascal/HP-UX Release Notes Version A.10.08

16 Chapter 1
New and Changed Features
Optimization Parameters
Table 1-3 Advanced Optimization Options
Advanced Option Optimization Performed
+O[no]fastaccess
Levels 0, 1, 2, 3, 4
+Ofastaccess optimizes for fast access to global data items.
Use +Ofastaccess to improve execution speed at the expense of
longer compile and link times.
At all optimization levels, except level 4, the default is
+Onofastaccess. At optimization level 4, the default is
+Ofastaccess.
+O[no]fltacc
Levels 2, 3, 4
The +Onofltacc option allows the compiler to perform
floating-point optimizations that are algebraically correct but
that may result in numerical differences. In general, these
differences will be insignificant. For example, this option may
change the order of expression evaluation as such: If a, b, and c
are floating-point variables, the expressions (a + b) + c and a
+ (b + c) may give slightly different results due to roundoff. In
general, these differences will be insignificant.
The +Onofltacc option also enables the optimizer to generate
fused multiply-add (FMA) instructions, the FMPYFADD and
FMPYNFADD. These instructions improve performance but
occasionally produce results that may differ from results
produced by code without FMA instructions. In general, the
differences are slight. FMA instructions are only available on
PA-RISC 2.0 systems. (continued on the next page)