doc/TestFloat-source.html

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<HEAD>
<TITLE>Berkeley TestFloat Source Documentation</TITLE>
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<H1>Berkeley TestFloat Release 3c: Source Documentation</H1>

<P>
John R. Hauser<BR>
2017 February 10<BR>
</P>


<H2>Contents</H2>

<BLOCKQUOTE>
<TABLE BORDER=0 CELLSPACING=0 CELLPADDING=0>
<COL WIDTH=25>
<COL WIDTH=*>
<TR><TD COLSPAN=2>1. Introduction</TD></TR>
<TR><TD COLSPAN=2>2. Limitations</TD></TR>
<TR><TD COLSPAN=2>3. Acknowledgments and License</TD></TR>
<TR><TD COLSPAN=2>4. TestFloat Package Directory Structure</TD></TR>
<TR><TD COLSPAN=2>5. Dependence on Berkeley SoftFloat</TD></TR>
<TR><TD COLSPAN=2>6. Issues for Porting TestFloat to a New Target</TD></TR>
<TR>
  <TD></TD>
  <TD>6.1. Standard Headers <CODE>&lt;stdbool.h&gt;</CODE> and
    <CODE>&lt;stdint.h&gt;</CODE></TD>
</TR>
<TR><TD></TD><TD>6.2. Standard Header <CODE>&lt;fenv.h&gt;</CODE></TD></TR>
<TR><TD></TD><TD>6.3. Macros for Build Options</TD></TR>
<TR><TD></TD><TD>6.4. Specializing the <CODE>testfloat</CODE> Program</TD></TR>
<TR><TD></TD><TD>6.5. Improving the Random Number Functions</TD></TR>
<TR><TD COLSPAN=2>7. Contact Information</TD></TR>
</TABLE>
</BLOCKQUOTE>


<H2>1. Introduction</H2>

<P>
This document gives information needed for compiling and/or porting Berkeley
TestFloat, a small collection of programs for testing that an implementation of
binary floating-point conforms to the IEEE Standard for Floating-Point
Arithmetic.
For basic documentation about TestFloat refer to
<A HREF="TestFloat-general.html"><NOBR><CODE>TestFloat-general.html</CODE></NOBR></A>.
</P>

<P>
The source code for TestFloat is intended to be relatively machine-independent.
Most programs in the TestFloat package should be compilable with any
ISO-Standard C compiler that also supports <NOBR>64-bit</NOBR> integers.
If the all-in-one <CODE>testfloat</CODE> program will be used to test a new
floating-point implementation, additional effort will likely be required to
retarget that program to invoke the new floating-point operations.
TestFloat has been successfully compiled with the GNU C Compiler
(<CODE>gcc</CODE>) for several platforms.
</P>

<P>
<NOBR>Release 3</NOBR> of TestFloat was a complete rewrite relative to
<NOBR>Release 2</NOBR> or earlier.
The current version of TestFloat is <NOBR>Release 3c</NOBR>.
</P>

<P>
TestFloat depends on Berkeley SoftFloat, which is a software implementation of
binary floating-point that conforms to the IEEE Standard for Floating-Point
Arithmetic.
SoftFloat is not included with the TestFloat sources.
It can be obtained from the Web page
<A HREF="http://www.jhauser.us/arithmetic/SoftFloat.html"><NOBR><CODE>http://www.jhauser.us/arithmetic/SoftFloat.html</CODE></NOBR></A>.
</P>


<H2>2. Limitations</H2>

<P>
TestFloat assumes the computer has an addressable byte size of either 8 or
<NOBR>16 bits</NOBR>.
(Nearly all computers in use today have <NOBR>8-bit</NOBR> bytes.)
</P>

<P>
TestFloat is written entirely <NOBR>in C</NOBR>.
The C compiler used must conform at a minimum to the 1989 ANSI standard for the
C language (same as the 1990 ISO standard) and must in addition support basic
arithmetic on <NOBR>64-bit</NOBR> integers.
Earlier releases of TestFloat were capable of testing <NOBR>32-bit</NOBR>
single-precision and <NOBR>64-bit</NOBR> double-precision floating-point
without requiring compiler support for <NOBR>64-bit</NOBR> integers, but this
option is not supported starting with <NOBR>Release 3</NOBR>.
Since 1999, ISO standards for C have mandated compiler support for
<NOBR>64-bit</NOBR> integers.
A compiler conforming to the 1999 C Standard or later is recommended but not
strictly required.
</P>

<P>
<NOBR>C Standard</NOBR> header files <CODE>&lt;stdbool.h&gt;</CODE> and
<CODE>&lt;stdint.h&gt;</CODE> are required for defining standard Boolean and
integer types.
If these headers are not supplied with the C compiler, minimal substitutes must
be provided.
TestFloat&rsquo;s dependence on these headers is detailed later in
<NOBR>section 6.1</NOBR>, <I>Standard Headers <CODE>&lt;stdbool.h&gt;</CODE>
and <CODE>&lt;stdint.h&gt;</CODE></I>.
</P>


<H2>3. Acknowledgments and License</H2>

<P>
The TestFloat package was written by me, <NOBR>John R.</NOBR> Hauser.
<NOBR>Release 3</NOBR> of TestFloat was a completely new implementation
supplanting earlier releases.
The project to create <NOBR>Release 3</NOBR> (now <NOBR>through 3c</NOBR>) was
done in the employ of the University of California, Berkeley, within the
Department of Electrical Engineering and Computer Sciences, first for the
Parallel Computing Laboratory (Par Lab) and then for the ASPIRE Lab.
The work was officially overseen by Prof. Krste Asanovic, with funding provided
by these sources:
<BLOCKQUOTE>
<TABLE>
<COL>
<COL WIDTH=10>
<COL>
<TR>
<TD VALIGN=TOP><NOBR>Par Lab:</NOBR></TD>
<TD></TD>
<TD>
Microsoft (Award #024263), Intel (Award #024894), and U.C. Discovery
(Award #DIG07-10227), with additional support from Par Lab affiliates Nokia,
NVIDIA, Oracle, and Samsung.
</TD>
</TR>
<TR>
<TD VALIGN=TOP><NOBR>ASPIRE Lab:</NOBR></TD>
<TD></TD>
<TD>
DARPA PERFECT program (Award #HR0011-12-2-0016), with additional support from
ASPIRE industrial sponsor Intel and ASPIRE affiliates Google, Nokia, NVIDIA,
Oracle, and Samsung.
</TD>
</TR>
</TABLE>
</BLOCKQUOTE>
</P>

<P>
The following applies to the whole of TestFloat <NOBR>Release 3c</NOBR> as well
as to each source file individually.
</P>

<P>
Copyright 2011, 2012, 2013, 2014, 2015, 2016, 2017 The Regents of the
University of California.
All rights reserved.
</P>

<P>
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
<OL>

<LI>
<P>
Redistributions of source code must retain the above copyright notice, this
list of conditions, and the following disclaimer.
</P>

<LI>
<P>
Redistributions in binary form must reproduce the above copyright notice, this
list of conditions, and the following disclaimer in the documentation and/or
other materials provided with the distribution.
</P>

<LI>
<P>
Neither the name of the University nor the names of its contributors may be
used to endorse or promote products derived from this software without specific
prior written permission.
</P>

</OL>
</P>

<P>
THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS &ldquo;AS IS&rdquo;,
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ARE
DISCLAIMED.
IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
</P>


<H2>4. TestFloat Package Directory Structure</H2>

<P>
Because TestFloat is targeted to multiple platforms, its source code is
slightly scattered between target-specific and target-independent directories
and files.
The supplied directory structure is as follows:
<BLOCKQUOTE>
<PRE>
doc
source
    subj-C
build
    template
    Linux-386-GCC
    Linux-386-SSE2-GCC
    Linux-x86_64-GCC
    Win32-MinGW
    Win32-SSE2-MinGW
    Win64-MinGW-w64
</PRE>
</BLOCKQUOTE>
The majority of the TestFloat sources are provided in the <CODE>source</CODE>
directory.
The <NOBR><CODE>subj-C</CODE></NOBR> subdirectory contains the sources that
configure the all-in-one <CODE>testfloat</CODE> program to test the C
compiler&rsquo;s implementation of the standard C types <CODE>float</CODE>,
<CODE>double</CODE>, and possibly <CODE>long</CODE> <CODE>double</CODE>.
The &lsquo;<CODE>subj</CODE>&rsquo; in <NOBR><CODE>subj-C</CODE></NOBR> is an
abbreviation of <I>subject</I>, referring to the floating-point that is the
subject of the test.
If <CODE>testfloat</CODE> is retargeted to test other floating-point
implementations, the corresponding source files would be expected to be in
other subdirectories alongside <NOBR><CODE>subj-C</CODE></NOBR>, with names of
the form <NOBR><CODE>subj-&lt;<I>target</I>&gt;</CODE></NOBR>.
More about retargeting <CODE>testfloat</CODE> is found in
<NOBR>section 6.4</NOBR>, <I>Specializing the <CODE>testfloat</CODE>
Program</I>.
</P>

<P>
The <CODE>build</CODE> directory is intended to contain a subdirectory for each
target platform for which builds of the TestFloat programs may be created.
For each build target, the target&rsquo;s subdirectory is where all derived
object files and the completed TestFloat executables are created.
The <CODE>template</CODE> subdirectory is not an actual build target but
contains sample files for creating new target directories.
</P>

<P>
Ignoring the <CODE>template</CODE> directory, the supplied target directories
are intended to follow a naming system of
<NOBR><CODE>&lt;<I>execution-environment</I>&gt;-&lt;<I>compiler</I>&gt;</CODE></NOBR>.
For the example targets,
<NOBR><CODE>&lt;<I>execution-environment</I>&gt;</CODE></NOBR> is
<NOBR><CODE>Linux-386</CODE></NOBR>, <NOBR><CODE>Linux-386-SSE2</CODE></NOBR>,
<NOBR><CODE>Linux-x86_64</CODE></NOBR>, <CODE>Win32</CODE>,
<NOBR><CODE>Win32-SSE2</CODE></NOBR>, or <CODE>Win64</CODE>, and
<NOBR><CODE>&lt;<I>compiler</I>&gt;</CODE></NOBR> is <CODE>GCC</CODE>,
<CODE>MinGW</CODE>, or <NOBR><CODE>MinGW-w64</CODE></NOBR>.
</P>

<P>
As supplied, each target directory contains two files:
<BLOCKQUOTE>
<PRE>
Makefile
platform.h
</PRE>
</BLOCKQUOTE>
The provided <CODE>Makefile</CODE> is written for GNU <CODE>make</CODE>.
A build of TestFloat for the specific target is begun by executing the
<CODE>make</CODE> command with the target directory as the current directory.
A completely different build tool can be used if an appropriate
<CODE>Makefile</CODE> equivalent is created.
</P>

<P>
The <CODE>platform.h</CODE> header file exists to provide a location for
additional C declarations specific to the build target.
Every C source file of TestFloat contains a <CODE>#include</CODE> for
<CODE>platform.h</CODE>.
In many cases, the contents of <CODE>platform.h</CODE> can be as simple as one
or two lines of code.
If the target&rsquo;s compiler or library has bugs or other shortcomings,
workarounds for these issues may be possible with target-specific declarations
in <CODE>platform.h</CODE>, without the need to modify the main TestFloat
sources.
</P>

<P>
It may not be necessary to build all of the TestFloat programs.
For testing a floating-point implementation, typically
<CODE>testfloat_gen</CODE> and <CODE>testfloat</CODE> will not both be used,
and <CODE>testfloat_ver</CODE> may not be needed either.
The Makefile (or equivalent) can be modified not to create unneeded programs.
This may be especially relevant for the all-in-one test program
<CODE>testfloat</CODE>, which might not build without special attention.
</P>


<H2>5. Dependence on Berkeley SoftFloat</H2>

<P>
In addition to the distributed sources, TestFloat depends on the existence of a
compatible Berkeley SoftFloat library and the corresponding header file
<CODE>softfloat.h</CODE>.
As mentioned earlier, SoftFloat is a separate package available at Web page
<A HREF="http://www.jhauser.us/arithmetic/SoftFloat.html"><NOBR><CODE>http://www.jhauser.us/arithmetic/SoftFloat.html</CODE></NOBR></A>.
The SoftFloat library must be compiled before the TestFloat programs can be
built.
In the example Makefiles, the locations of the SoftFloat header files and
pre-compiled library are specified by these macros:
<BLOCKQUOTE>
<DL>
<DT><CODE>SOFTFLOAT_INCLUDE_DIR</CODE>
<DD>
The path of the directory containing <CODE>softfloat.h</CODE>, as well as other
nonstandard header files referenced by <CODE>softfloat.h</CODE>, if any.
<DT><CODE>SOFTFLOAT_H</CODE>
<DD>
A list of the full paths of all SoftFloat header files needed by SoftFloat
clients.  This list must include <CODE>softfloat.h</CODE> and may also include
other header files referenced by <CODE>softfloat.h</CODE>, such as
<CODE>softfloat_types.h</CODE>.
This macro is used only to establish build dependencies between the SoftFloat
header files and TestFloat&rsquo;s source files, in case the SoftFloat header
files are changed.
<DT><CODE>SOFTFLOAT_LIB</CODE>
<DD>
The full path of the compiled SoftFloat library (usually
<CODE>softfloat.a</CODE> or <CODE>libsoftfloat.a</CODE>).
</DL>
</BLOCKQUOTE>
</P>


<H2>6. Issues for Porting TestFloat to a New Target</H2>

<H3>6.1. Standard Headers <CODE>&lt;stdbool.h&gt;</CODE> and <CODE>&lt;stdint.h&gt;</CODE></H3>

<P>
The TestFloat sources make use of standard headers
<CODE>&lt;stdbool.h&gt;</CODE> and <CODE>&lt;stdint.h&gt;</CODE>, which have
been part of the ISO C Standard Library since 1999.
With any recent compiler, these standard headers are likely to be supported,
even if the compiler does not claim complete conformance to the latest ISO C
Standard.
For older or nonstandard compilers, substitutes for
<CODE>&lt;stdbool.h&gt;</CODE> and <CODE>&lt;stdint.h&gt;</CODE> may need to be
created.
TestFloat depends on these names from <CODE>&lt;stdbool.h&gt;</CODE>:
<BLOCKQUOTE>
<PRE>
bool
true
false
</PRE>
</BLOCKQUOTE>
and on these names from <CODE>&lt;stdint.h&gt;</CODE>:
<BLOCKQUOTE>
<PRE>
uint16_t
uint32_t
uint64_t
int32_t
int64_t
UINT64_C
INT64_C
uint_least8_t
uint_fast8_t
uint_fast16_t
uint_fast32_t
uint_fast64_t
int_fast8_t
int_fast16_t
int_fast32_t
int_fast64_t
</PRE>
</BLOCKQUOTE>
</P>


<H3>6.2. Standard Header <CODE>&lt;fenv.h&gt;</CODE></H3>

<P>
Because the supplied all-in-one <CODE>testfloat</CODE> program tests the
floating-point operations of the C language, it uses the facilities provided by
standard C header <CODE>&lt;fenv.h&gt;</CODE> to access the floating-point
environment of C, in particular to set the rounding mode and to access the
floating-point exception flags.
Like <CODE>&lt;stdbool.h&gt;</CODE> and <CODE>&lt;stdint.h&gt;</CODE>,
<CODE>&lt;fenv.h&gt;</CODE> has been part of the ISO C Standard Library since
1999, but older or nonstandard C compilers may not support it.
</P>

<P>
Some form of standard header <CODE>&lt;fenv.h&gt;</CODE> is needed only if the
<CODE>testfloat</CODE> program is wanted <EM>and</EM> the program will not be
retargeted to invoke a floating-point implementation in a way that bypasses the
standard C environment.
Typically, if <CODE>testfloat</CODE> is wanted, it will be retargeted to invoke
a new floating-point implementation directly, making
<CODE>&lt;fenv.h&gt;</CODE> irrelevant.
For more about retargeting <CODE>testfloat</CODE>, see <NOBR>section 6.4</NOBR>
below, <I>Specializing the <CODE>testfloat</CODE> Program</I>.
</P>


<H3>6.3. Macros for Build Options</H3>

<P>
The TestFloat source files are affected by several C preprocessor macros:
<BLOCKQUOTE>
<DL>
<DT><CODE>LITTLEENDIAN</CODE>
<DD>
Must be defined for little-endian machines;
must not be defined for big-endian machines.
<DT><CODE>INLINE</CODE>
<DD>
Can be defined to a sequence of tokens used to indicate that a C function
should be inlined.
If the compiler does not support the inlining of functions, this macro must not
be defined.
For compilers that conform to the C Standard&rsquo;s rules for inline
functions, this macro can be defined as the single keyword <CODE>inline</CODE>.
For other compilers that follow a convention pre-dating the standardization of
<CODE>inline</CODE>, this macro may need to be defined to <CODE>extern</CODE>
<CODE>inline</CODE>.
<DT><CODE>THREAD_LOCAL</CODE>
<DD>
Can be defined to a sequence of tokens that, when appearing at the start of a
variable declaration, indicates to the C compiler that the variable is
<I>per-thread</I>, meaning that each execution thread gets its own separate
instance of the variable.
This macro is used in the supplied version of Berkeley SoftFloat&rsquo;s header
<CODE>softfloat.h</CODE>, in the declarations of variables
<CODE>softfloat_roundingMode</CODE>, <CODE>softfloat_detectTininess</CODE>,
<CODE>extF80_roundingPrecision</CODE>, and
<CODE>softfloat_exceptionFlags</CODE>.
To use the supplied, unmodified header <CODE>softfloat.h</CODE>, this macro
must be defined (or not defined) the same as when the SoftFloat library was
built.
</DL>
<DL>
<DT><CODE>FLOAT16</CODE>
<DD>
Must be defined if the TestFloat programs are to support the
<NOBR>16-bit</NOBR> half-precision floating-point format.
<DT><CODE>FLOAT64</CODE>
<DD>
Must be defined if the TestFloat programs are to support the
<NOBR>64-bit</NOBR> double-precision floating-point format.
<DT><CODE>EXTFLOAT80</CODE>
<DD>
Must be defined if the TestFloat programs are to support the
<NOBR>80-bit</NOBR> double-extended-precision floating-point format.
<DT><CODE>FLOAT128</CODE>
<DD>
Must be defined if the TestFloat programs are to support the
<NOBR>128-bit</NOBR> quadruple-precision floating-point format.
<DT><CODE>FLOAT_ROUND_ODD</CODE>
<DD>
Must be defined if the TestFloat programs are to support rounding to odd
(jamming).
To be useful, this option also requires that the Berkeley SoftFloat library was
compiled with macro <CODE>SOFTFLOAT_ROUND_ODD</CODE> defined.
</DL>
</BLOCKQUOTE>
Following the usual custom <NOBR>for C</NOBR>, for all the macros except
<CODE>INLINE</CODE> and <CODE>THREAD_LOCAL</CODE>, the content of a
macro&rsquo;s definition is irrelevant;
what matters is a macro&rsquo;s effect on <CODE>#ifdef</CODE> directives.
</P>

<P>
It is recommended that any definition of macros <CODE>LITTLEENDIAN</CODE>,
<CODE>INLINE</CODE>, and <CODE>THREAD_LOCAL</CODE> be made in a build
target&rsquo;s <CODE>platform.h</CODE> header file, because these macros are
expected to be determined inflexibly by the target machine and compiler.
The other five macros select build options, and hence might be better located
in the target&rsquo;s Makefile (or its equivalent).
</P>


<H3>6.4. Specializing the <CODE>testfloat</CODE> Program</H3>

<P>
The supplied sources for the all-in-one <CODE>testfloat</CODE> program cause
<CODE>testfloat</CODE> to test the C compiler&rsquo;s <CODE>float</CODE> and
<CODE>double</CODE> types for C operations <CODE>+</CODE>, <CODE>-</CODE>,
<CODE>*</CODE>, <CODE>/</CODE>, etc.
The supplied version is also capable of testing C type <CODE>long</CODE>
<CODE>double</CODE> if the sources are compiled with one of these macros
defined:
<BLOCKQUOTE>
<DL>
<DT><CODE>LONG_DOUBLE_IS_EXTFLOAT80</CODE>
<DD>
Indicates that type <CODE>long</CODE> <CODE>double</CODE> is
<NOBR>80-bit</NOBR> double-extended-precision floating-point.
<DT><CODE>LONG_DOUBLE_IS_FLOAT128</CODE>
<DD>
Indicates that type <CODE>long</CODE> <CODE>double</CODE> is
<NOBR>128-bit</NOBR> quadruple-precision floating-point.
</DL>
</BLOCKQUOTE>
By default, <CODE>testfloat</CODE> assumes that only the IEEE Standard&rsquo;s
original four rounding modes (<CODE>near_even</CODE>, <CODE>minMag</CODE>,
<CODE>min</CODE>, and <CODE>max</CODE>) are supported by the floating-point
being tested.
For other rounding modes, additional macro can be defined:
<BLOCKQUOTE>
<DL>
<DT><CODE>SUBJFLOAT_ROUND_NEAR_MAXMAG</CODE>
<DD>
Indicates that the subject floating-point supports rounding mode
<CODE>near_maxMag</CODE> (nearest/away).
<DT><CODE>SUBJFLOAT_ROUND_ODD</CODE>
<DD>
Indicates that the subject floating-point supports rounding mode
<CODE>odd</CODE> (jamming).
</DL>
</BLOCKQUOTE>
</P>

<P>
To test a new and/or different implementation of floating-point,
<CODE>testfloat</CODE> must normally be retargeted to invoke this other
floating-point instead of C&rsquo;s floating-point.
Two source files define the functions that <CODE>testfloat</CODE> uses to
invoke floating-point operations for testing:
<BLOCKQUOTE>
<PRE>
subjfloat_config.h
subjfloat.c
</PRE>
</BLOCKQUOTE>
For the default target of testing C&rsquo;s floating-point, these files are
contained in directory <NOBR><CODE>source/subj-C</CODE></NOBR> as discussed
earlier.
For a different subject floating-point, it is recommended that appropriate
versions of <CODE>subjfloat_config.h</CODE> and <CODE>subjfloat.c</CODE> be
stored in a sibling <NOBR><CODE>subj-&lt;<I>target</I>&gt;</CODE></NOBR>
directory, where <CODE>&lt;<I>target</I>&gt;</CODE> names the particular
target.
</P>

<P>
Header file <CODE>subjfloat_config.h</CODE> defines a macro of the form
<CODE>SUBJ_*</CODE> for each subject function supported.
For example, if function <CODE>subj_f32_add</CODE> exists to perform
<NOBR>32-bit</NOBR> floating-point addition, then
<CODE>subjfloat_config.h</CODE> should have a definition for macro
<CODE>SUBJ_F32_ADD</CODE>.
The actual function <CODE>subj_f32_add</CODE> is expected to be defined in
<CODE>subjfloat.c</CODE>, along with all other subject functions.
A common header file, <CODE>subjfloat.h</CODE>, (not target-specific) provides
prototype declarations for all possible subject functions that
<CODE>testfloat</CODE> may be compiled to test, whether actually existing or
not.
(There is no penalty for the header to declare prototypes of nonexistent
functions that are never called.)
For a specific build of <CODE>testfloat</CODE>, the <CODE>-list</CODE> option
will list all subject functions that the <CODE>testfloat</CODE> program is able
to invoke and thus test.
</P>

<P>
In the source code as supplied, macros <CODE>LONG_DOUBLE_IS_EXTFLOAT80</CODE>
and <CODE>LONG_DOUBLE_IS_FLOAT128</CODE> affect only the target-specific source
files in <NOBR><CODE>source/subj-C</CODE></NOBR>, so these macros can be
ignored for any other subject floating-point that does not depend on them.
On the other hand, macros <CODE>SUBJFLOAT_ROUND_NEAR_MAXMAG</CODE> and
<CODE>SUBJFLOAT_ROUND_ODD</CODE> always determine whether the
<CODE>testfloat</CODE> program attempts to test rounding modes
<CODE>near_maxMag</CODE> and <CODE>odd</CODE>, regardless of the subject
floating-point.
</P>


<H3>6.5. Improving the Random Number Functions</H3>

<P>
If you are serious about using TestFloat for testing floating-point, you should
consider replacing the random number functions in <CODE>random.c</CODE>.
The supplied random number functions are built on top of the standard C
<CODE>rand</CODE> function.
Because function <CODE>rand</CODE> is rather poor on some systems, the
functions in <CODE>random.c</CODE> assume very little about the quality of
<CODE>rand</CODE>.
As a result, <CODE>rand</CODE> is called more frequently than it might need to
be, shortening the time before random number sequences repeat, and possibly
wasting time as well.
If <CODE>rand</CODE> is better on a given target platform, or if another,
better random number generator is available (such as <CODE>rand48</CODE> on
UNIX-derived systems), TestFloat can be improved by overriding the given
<CODE>random.c</CODE> with a target-specific one.
</P>

<P>
Rather than modifying the supplied file <CODE>random.c</CODE>, it is
recommended instead that a new, alternate file be created and the
target&rsquo;s Makefile be modified to refer to that alternate file in place of
<CODE>random.c</CODE>.
</P>


<H2>7. Contact Information</H2>

<P>
At the time of this writing, the most up-to-date information about TestFloat
and the latest release can be found at the Web page
<A HREF="http://www.jhauser.us/arithmetic/TestFloat.html"><NOBR><CODE>http://www.jhauser.us/arithmetic/TestFloat.html</CODE></NOBR></A>.
</P>


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