xref: /src/regress/lib/libc/ieeefp/testfloat/notes/testfloat-source.txt

TestFloat Release 2a Source Documentation

John R. Hauser
1998 December 16


-------------------------------------------------------------------------------
Introduction

TestFloat is a program for testing that a floating-point implementation
conforms to the IEC/IEEE Standard for Binary Floating-Point Arithmetic.
All standard operations supported by the system can be tested, except for
conversions to and from decimal.  Any of the following machine formats can
be tested:  single precision, double precision, extended double precision,
and/or quadruple precision.  Testing extended double-precision or quadruple-
precision formats requires a C compiler that supports 64-bit integer
arithmetic.

This document gives information needed for compiling and/or porting
TestFloat.

The source code for TestFloat is intended to be relatively machine-
independent.  TestFloat is written in C, and should be compilable using
any ISO/ANSI C compiler.  At the time of this writing, the program has
been successfully compiled using the GNU C Compiler (`gcc') for several
platforms.  Because ISO/ANSI C does not provide access to some features
of IEC/IEEE floating-point such as the exception flags, porting TestFloat
unfortunately involves some machine-dependent coding.

TestFloat depends on SoftFloat, which is a software implementation of
floating-point that conforms to the IEC/IEEE Standard.  SoftFloat is not
included with the TestFloat sources.  It can be obtained from the Web
page `http://HTTP.CS.Berkeley.EDU/~jhauser/arithmetic/SoftFloat.html'.

In addition to a program for testing a machine's floating-point, the
TestFloat package includes a variant for testing SoftFloat called
`testsoftfloat'.  The sources for both programs are intermixed, and both are
described here.

The first release of TestFloat (Release 1) was called _FloatTest_.  The old
name has been obsolete for some time.


-------------------------------------------------------------------------------
Limitations

TestFloat as written requires an ISO/ANSI-style C compiler.  No attempt has
been made to accommodate compilers that are not ISO-conformant.  Older ``K&R-
style'' compilers are not adequate for compiling TestFloat.  All testing I
have done so far has been with the GNU C Compiler.  Compilation with other
compilers should be possible but has not been tested.

The TestFloat sources assume that source code file names can be longer than
8 characters.  In order to compile under an MS-DOS-style system, many of the
source files will need to be renamed, and the source and makefiles edited
appropriately.  Once compiled, the TestFloat program does not depend on the
existence of long file names.

The underlying machine is assumed to be binary with a word size that is a
power of 2.  Bytes are 8 bits.  Testing of extended double-precision and
quadruple-precision formats depends on the C compiler implementing a 64-bit
integer type.  If the largest integer type supported by the C compiler is
32 bits, only single- and double-precision operations can be tested.


-------------------------------------------------------------------------------
Contents

    Introduction
    Limitations
    Contents
    Legal Notice
    TestFloat Source Directory Structure
    Target-Independent Modules
    Target-Specific Modules
    Target-Specific Header Files
        processors/*.h
        testfloat/*/milieu.h
    Target-Specific Floating-Point Subroutines
    Steps to Creating the TestFloat Executables
    Improving the Random Number Generator
    Contact Information



-------------------------------------------------------------------------------
Legal Notice

TestFloat was written by John R. Hauser.

THIS SOFTWARE IS DISTRIBUTED AS IS, FOR FREE.  Although reasonable effort
has been made to avoid it, THIS SOFTWARE MAY CONTAIN FAULTS THAT WILL AT
TIMES RESULT IN INCORRECT BEHAVIOR.  USE OF THIS SOFTWARE IS RESTRICTED TO
PERSONS AND ORGANIZATIONS WHO CAN AND WILL TAKE FULL RESPONSIBILITY FOR ANY
AND ALL LOSSES, COSTS, OR OTHER PROBLEMS ARISING FROM ITS USE.


-------------------------------------------------------------------------------
TestFloat Source Directory Structure

Because TestFloat is targeted to multiple platforms, its source code
is slightly scattered between target-specific and target-independent
directories and files.  The directory structure is as follows:

    processors
    testfloat
        templates
        386-Win32-gcc
        SPARC-Solaris-gcc

The two topmost directories and their contents are:

    testfloat    - Most of the source code needed for TestFloat.
    processors   - Target-specific header files that are not specific to
                       TestFloat.

Within the `testfloat' directory are subdirectories for each of the
targeted platforms.  The TestFloat source code is distributed with targets
`386-Win32-gcc' and `SPARC-Solaris-gcc' (and perhaps others) already
prepared.  These can be used as examples for porting to new targets.  Source
files that are not within these target-specific subdirectories are intended
to be target-independent.

The naming convention used for the target-specific directories is
`<processor>-<executable-type>-<compiler>'.  The names of the supplied
target directories should be interpreted as follows:

  <processor>:
    386          - Intel 386-compatible processor.
    SPARC        - SPARC processor (as used by Sun machines).
  <executable-type>:
    Win32        - Microsoft Win32 executable.
    Solaris      - Sun Solaris executable.
  <compiler>:
    gcc          - GNU C Compiler.

You do not need to maintain this convention if you do not want to.

Alongside the supplied target-specific directories there is a `templates'
directory containing a set of ``generic'' target-specific source files.
A new target directory can be created by copying the `templates' directory
and editing the files inside.  (Complete instructions for porting TestFloat
to a new target are in the section _Steps_to_Creating_the_TestFloat_
_Executables_.)  Note that the `templates' directory will not work as a
target directory without some editing.  To avoid confusion, it would be wise
to refrain from editing the files inside `templates' directly.

In addition to the distributed sources, TestFloat depends on the existence
of an appropriately-compiled SoftFloat binary and the corresponding header
file `softfloat.h'.  SoftFloat is not included with the TestFloat sources.
It can be obtained from the Web page `http://HTTP.CS.Berkeley.EDU/~jhauser/
arithmetic/SoftFloat.html'.

As distributed, the makefiles for TestFloat assume the existence of three
sibling directories:

    processors
    softfloat
    testfloat

Only the `processors' and `testfloat' directories are included in the
TestFloat package.  The `softfloat' directory is assumed to contain a
target-specific subdirectory within which the SoftFloat header file and
compiled binary can be found.  (See the source documentation accompanying
SoftFloat.)  The `processors' directory distributed with TestFloat is
intended to be identical to that included with the SoftFloat source.

These are the defaults, but other organizations of the sources are possible.
The TestFloat makefiles and `milieu.h' files (see below) are easily edited
to accommodate other arrangements.


-------------------------------------------------------------------------------
Target-Independent Modules

The TestFloat program is composed of a number of modules, some target-
specific and some target-independent.  The target-independent modules are as
follows:

-- The `fail' module provides a common routine for writing an error message
   and aborting.

-- The `random' module generates random integer values.

-- The `writeHex' module defines routines for writing the various types in
   the hexadecimal form used by TestFloat.

-- The `testCases' module generates test cases for the various types.

-- The `testLoops' module contains various routines for exercising two
   implementations of a function and reporting any differences observed.

-- The `slowfloat' module provides the simple floating-point implementation
   used by `testsoftfloat' for comparing against SoftFloat.  The heart
   of `slowfloat' is found in either `slowfloat-32' or `slowfloat-64',
   depending on whether the `BITS64' macro is defined.

-- The `systfloat' module gives a SoftFloat-like interface to the machine's
   floating-point.

-- The `testFunction' module implements `testfloat's main loop for testing a
   function for all of the relevant rounding modes and rounding precisions.
   (The `testsoftfloat' program contains its own version of this code.)

-- The `testfloat' and `testsoftfloat' modules are the main modules for the
   `testfloat' and `testsoftfloat' programs.

Except possibly for `systfloat', these modules should not need to be
modified.

The `systfloat' module uses the floating-point operations of the C language
to access a machine's floating-point.  Unfortunately, some IEC/IEEE
floating-point operations are not accessible within ISO/ANSI C.  The
following machine functions cannot be tested unless an alternate `systfloat'
module is provided:

    <float>_to_int32 (rounded according to rounding mode)
    <float>_to_int64 (rounded according to rounding mode)
    <float>_round_to_int
    <float>_rem
    <float>_sqrt, except float64_sqrt
    <float>_eq_signaling
    <float>_le_quiet
    <float>_lt_quiet

The `-list' option to `testfloat' will show the operations the program is
prepared to test.  The section _Target-Specific_Floating-Point_Subroutines_
later in this document explains how to create a target-specific `systfloat'
module to change the set of testable functions.


-------------------------------------------------------------------------------
Target-Specific Modules

No target-specific modules are needed for `testsoftfloat'.

The `testfloat' program uses two target-specific modules:

-- The `systmodes' module defines functions for setting the modes
   controlling the system's floating-point, including the rounding mode and
   the rounding precision for extended double precision.

-- The `systflags' module provides a function for clearing and examining the
   system's floating-point exception flags.

These modules must be supplied for each target.  They can be implemented in
any way desired, so long as all is reflected in the target's makefile.  For
the targets that come with the distributed source, each of these modules is
implemented as a single assembly language or C language source file.


-------------------------------------------------------------------------------
Target-Specific Header Files

The purpose of the two target-specific header files is detailed below.
In the following, the `*' symbol is used in place of the name of a specific
target, such as `386-Win32-gcc' or `SPARC-Solaris-gcc', or in place of some
other text as explained below.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
processors/*.h

The target-specific `processors' header file defines integer types
of various sizes, and also defines certain C preprocessor macros that
characterize the target.  The two examples supplied are `386-gcc.h' and
`SPARC-gcc.h'.  The naming convention used for processor header files is
`<processor>-<compiler>.h'.  The `processors' header file used to compile
TestFloat should be the same as that used to compile SoftFloat.

If 64-bit integers are supported by the compiler, the macro name `BITS64'
should be defined here along with the corresponding 64-bit integer
types.  In addition, the function-like macro `LIT64' must be defined for
constructing 64-bit integer literals (constants).  The `LIT64' macro is used
consistently in the TestFloat code to annotate 64-bit literals.

If an inlining attribute (such as an `inline' keyword) is provided by the
compiler, the macro `INLINE' should be defined to the appropriate keyword.
If not, `INLINE' can be set to the keyword `static'.  The `INLINE' macro
appears in the TestFloat source code before every function that should be
inlined by the compiler.

For maximum flexibility, the TestFloat source files do not include the
`processors' header file directly; rather, this file is included by the
target-specific `milieu.h' header, and `milieu.h' is included by the source
files.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
testfloat/*/milieu.h

The `milieu.h' header file provides declarations that are needed to
compile TestFloat.  In particular, it is through this header file that
the appropriate `processors' header is included to characterize the target
processor.  In addition, deviations from ISO/ANSI C by the compiler (such as
names not properly declared in system header files) are corrected in this
header if possible.

If the preprocessor macro `BITS64' is defined in the `processors' header
file but only the 32-bit version of SoftFloat is actually used, the `BITS64'
macro should be undefined here after the `processors' header has defined it.

If the C compiler implements the `long double' floating-point type of C
as extended double precision, then `LONG_DOUBLE_IS_FLOATX80' should be
defined here.  Alternatively, if the C `long double' type is implemented as
quadruple precision, `LONG_DOUBLE_IS_FLOAT128' should be defined.  At most
one of these macros should be defined.  A C compiler is allowed to implement
`long double' the same as `double', in which case neither of these macros
should be defined.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


-------------------------------------------------------------------------------
Target-Specific Floating-Point Subroutines

This section applies only to `testfloat' and not to `testsoftfloat'.

By default, TestFloat tests a machine's floating-point by testing the
floating-point operations of the C language.  Unfortunately, some IEC/IEEE
floating-point operations are not defined within ISO/ANSI C.  If a machine
implements such ``non-C'' operations, target-specific subroutines for
the operations can be supplied to allow TestFloat to test these machine
features.  Typically, such subroutines will need to be written in assembly
language, although equivalent functions can sometimes be found among the
system's software libraries.

The following machine functions cannot be tested by TestFloat unless target-
specific subroutines are supplied for them:

    <float>_to_int32 (rounded according to rounding mode)
    <float>_to_int64 (rounded according to rounding mode)
    <float>_round_to_int
    <float>_rem
    <float>_sqrt, except float64_sqrt
    <float>_eq_signaling
    <float>_le_quiet
    <float>_lt_quiet

In addition to these, none of the `floatx80' functions can be tested by
default if the C `long double' type is something other than extended double
precision; and likewise, none of the `float128' functions can be tested by
default if `long double' is not quadruple precision.  Since `long double'
cannot be both extended double precision and quadruple precision at the
same time, at least one of these types cannot be tested by TestFloat without
appropriate subroutines being supplied for that type.  (On the other hand,
few systems implement _both_ extended double-precision and quadruple-
precision floating-point; and unless a system does implement both, it does
not need both tested.)

Note that the `-list' option to `testfloat' will show the operations
TestFloat is prepared to test.

TestFloat's `systfloat' module supplies the system version of the functions
to be tested.  The names of the `systfloat' subroutines are the same as the
function names used as arguments to the `testfloat' command but with `syst_'
prefixed--thus, for example, `syst_float32_add' and `syst_int32_to_float32'.
The default `systfloat' module maps these system functions to the standard
C operations; so `syst_float32_add', for example, is implemented using the
C `+' operation for the single-precision `float' type.  For each system
function supplied by `systfloat', a corresponding `SYST_<function>'
preprocessor macro is defined in `systfloat.h' to indicate that the function
exists to be tested (e.g., `SYST_FLOAT32_ADD').  The `systfloat.h' header
file also declares function prototypes for the `systfloat' functions.

(The `systfloat.h' file that comes with the TestFloat package declares
prototypes for all of the possible `systfloat' functions, whether defined in
`systfloat' or not.  There is no penalty for declaring a function prototype
that is never used.)

A target-specific version of the `systfloat' module can easily be created to
replace the generic one.  This in fact has been done for the example targets
`386-Win32-gcc' and `SPARC-Solaris-gcc'.  For each target, an assembly
language `systfloat.S' has been created in the target directory along with
a corresponding `systfloat.h' header file defining the `SYST_<function>'
macros for the functions implemented.  The makefiles of the targets have
been edited to use these target-specific versions of `systfloat' rather than
the generic one.

The `systfloat' modules of the example targets have been written entirely
in assembly language in order to bypass any peculiarities of the C compiler.
Although this is probably a good idea, it is certainly not required.


-------------------------------------------------------------------------------
Steps to Creating the TestFloat Executables

Porting and/or compiling TestFloat involves the following steps:

1. Port SoftFloat and create a SoftFloat binary.  (Refer to the
   documentation accompanying SoftFloat.)

2. If one does not already exist, create an appropriate target-specific
   subdirectory under `testfloat' by copying the given `templates'
   directory.  The remaining steps occur within the target-specific
   subdirectory.

3. Edit the files `milieu.h' and `Makefile' to reflect the current
   environment.

4. Make `testsoftfloat' by executing `make testsoftfloat' (or `make
   testsoftfloat.exe', or whatever the `testsoftfloat' executable is
   called).  Verify that SoftFloat is working correctly by testing it with
   `testsoftfloat'.

If you only wanted `testsoftfloat', you are done.  The steps for `testfloat'
continue:

5. In the target-specific subdirectory, implement the `systmodes' and
   `systflags' modules.  (The `syst_float_set_rounding_precision' function
   need not do anything if the system does not support extended double
   precision.)

6. If the target machine supports standard floating-point functions that are
   not accessible within ISO/ANSI C, or if the C compiler cannot be trusted
   to use the machine's floating-point directly, create a target-specific
   `systfloat' module.

7. In the target-specific subdirectory, execute `make'.


-------------------------------------------------------------------------------
Improving the Random Number Generator

If you are serious about using TestFloat for testing floating-point, you
should consider replacing the supplied `random.c' with a better target-
specific one.  The standard C `rand' function is rather poor on some
systems, and consequently `random.c' has been written to assume very little
about the quality of `rand'.  As a result, the `rand' function is called
more frequently than it might need to be, shortening the time before
the random number generator repeats, and possibly wasting time as well.
If `rand' is better on your system, or if another better random number
generator is available (such as `rand48' on most Unix systems), TestFloat
can be improved by overriding the given `random.c' with a target-specific
one.


-------------------------------------------------------------------------------
Contact Information

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 `http://
HTTP.CS.Berkeley.EDU/~jhauser/arithmetic/TestFloat.html'.