JavaScript is required to for searching.
Skip Navigation Links
Exit Print View
Oracle Solaris Studio 12.3: C User's Guide     Oracle Solaris Studio 12.3 Information Library
search filter icon
search icon

Document Information


1.  Introduction to the C Compiler

2.  C-Compiler Implementation-Specific Information

2.1 Constants

2.1.1 Integral Constants

2.1.2 Character Constants

2.2 Linker Scoping Specifiers

2.3 Thread Local Storage Specifier

2.4 Floating Point, Nonstandard Mode

2.5 Labels as Values

2.6 long long Data Type

2.6.1 Printing long long Data Types

2.6.2 Usual Arithmetic Conversions

2.7 Case Ranges in Switch Statements

2.8 Assertions

2.9 Supported Attributes

2.10 Warnings and Errors

2.11 Pragmas

2.11.1 align

2.11.2 c99

2.11.3 does_not_read_global_data

2.11.4 does_not_return

2.11.5 does_not_write_global_data

2.11.6 dumpmacros

2.11.7 end_dumpmacros

2.11.8 error_messages

2.11.9 fini

2.11.10 hdrstop

2.11.11 ident

2.11.12 init

2.11.13 inline

2.11.14 int_to_unsigned

2.11.15 must_have_frame

2.11.16 nomemorydepend

2.11.17 no_side_effect

2.11.18 opt

2.11.19 pack

2.11.20 pipeloop

2.11.21 rarely_called

2.11.22 redefine_extname

2.11.23 returns_new_memory

2.11.24 unknown_control_flow

2.11.25 unroll

2.11.26 warn_missing_parameter_info

2.11.27 weak

2.12 Predefined Names

2.13 Preserving the Value of errno

2.14 Extensions

2.14.1 _Restrict Keyword

2.14.2 __asm Keyword

2.14.3 __inline and __inline__

2.14.4 __builtin_constant_p()


2.15 Environment Variables




2.15.4 TMPDIR

2.16 How to Specify Include Files

2.16.1 Using the -I- Option to Change the Search Algorithm Warnings

2.17 Compiling in Free-Standing Environments

2.18 Compiler Support for Intel MMX and Extended x86 Platform Intrinsics

3.  Parallelizing C Code

4.  lint Source Code Checker

5.  Type-Based Alias Analysis

6.  Transitioning to ISO C

7.  Converting Applications for a 64-Bit Environment

8.  cscope: Interactively Examining a C Program

A.  Compiler Options Grouped by Functionality

B.  C Compiler Options Reference

C.  Implementation-Defined ISO/IEC C99 Behavior

D.  Features of C99

E.  Implementation-Defined ISO/IEC C90 Behavior

F.  ISO C Data Representations

G.  Performance Tuning

H.  Oracle Solaris Studio C: Differences Between K&R C and ISO C


2.4 Floating Point, Nonstandard Mode

This section provides a summary of IEEE 754 floating-point default arithmetic, which is “nonstop.” Underflows are “gradual.” For more detailed information, see the Numerical Computation Guide.

Nonstop means that execution does not halt on occurrences like division by zero, floating-point overflow, or invalid operation exceptions. For example, consider the following, where x is zero and y is positive:

z = y / x;

By default, z is set to the value +Inf, and execution continues. With the -fnonstd option, however, this code causes an exit, such as a core dump.

The following example shows how gradual underflow works. Suppose you have the following code:

x = 10;
for (i = 0; i < LARGE_NUMBER; i++)
x = x / 10;

The first time through the loop, x is set to 1; the second time to 0.1; the third time to 0.01; and so on. Eventually, x reaches the lower limit of the machine’s capacity to represent its value. What happens the next time the loop runs?

Say that the smallest number characterizable is 1.234567e-38

The next time the loop runs, the number is modified by “stealing” from the mantissa and “giving” to the exponent so the new value is 1.23456e-39 and, subsequently, 1.2345e-40 and so on. This behavior is known as “gradual underflow,” and is the default. In nonstandard mode, none of this “stealing” takes place, and x is simply set to zero.