445 lines
20 KiB
Plaintext
445 lines
20 KiB
Plaintext
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TestFloat Release 2a Source Documentation
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John R. Hauser
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1998 December 16
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-------------------------------------------------------------------------------
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Introduction
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TestFloat is a program for testing that a floating-point implementation
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conforms to the IEC/IEEE Standard for Binary Floating-Point Arithmetic.
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All standard operations supported by the system can be tested, except for
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conversions to and from decimal. Any of the following machine formats can
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be tested: single precision, double precision, extended double precision,
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and/or quadruple precision. Testing extended double-precision or quadruple-
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precision formats requires a C compiler that supports 64-bit integer
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arithmetic.
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This document gives information needed for compiling and/or porting
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TestFloat.
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The source code for TestFloat is intended to be relatively machine-
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independent. TestFloat is written in C, and should be compilable using
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any ISO/ANSI C compiler. At the time of this writing, the program has
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been successfully compiled using the GNU C Compiler (`gcc') for several
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platforms. Because ISO/ANSI C does not provide access to some features
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of IEC/IEEE floating-point such as the exception flags, porting TestFloat
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unfortunately involves some machine-dependent coding.
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TestFloat depends on SoftFloat, which is a software implementation of
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floating-point that conforms to the IEC/IEEE Standard. SoftFloat is not
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included with the TestFloat sources. It can be obtained from the Web
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page `http://HTTP.CS.Berkeley.EDU/~jhauser/arithmetic/SoftFloat.html'.
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In addition to a program for testing a machine's floating-point, the
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TestFloat package includes a variant for testing SoftFloat called
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`testsoftfloat'. The sources for both programs are intermixed, and both are
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described here.
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The first release of TestFloat (Release 1) was called _FloatTest_. The old
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name has been obsolete for some time.
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-------------------------------------------------------------------------------
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Limitations
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TestFloat as written requires an ISO/ANSI-style C compiler. No attempt has
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been made to accommodate compilers that are not ISO-conformant. Older ``K&R-
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style'' compilers are not adequate for compiling TestFloat. All testing I
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have done so far has been with the GNU C Compiler. Compilation with other
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compilers should be possible but has not been tested.
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The TestFloat sources assume that source code file names can be longer than
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8 characters. In order to compile under an MS-DOS-style system, many of the
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source files will need to be renamed, and the source and makefiles edited
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appropriately. Once compiled, the TestFloat program does not depend on the
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existence of long file names.
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The underlying machine is assumed to be binary with a word size that is a
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power of 2. Bytes are 8 bits. Testing of extended double-precision and
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quadruple-precision formats depends on the C compiler implementing a 64-bit
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integer type. If the largest integer type supported by the C compiler is
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32 bits, only single- and double-precision operations can be tested.
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-------------------------------------------------------------------------------
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Contents
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Introduction
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Limitations
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Contents
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Legal Notice
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TestFloat Source Directory Structure
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Target-Independent Modules
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Target-Specific Modules
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Target-Specific Header Files
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processors/*.h
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testfloat/*/milieu.h
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Target-Specific Floating-Point Subroutines
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Steps to Creating the TestFloat Executables
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Improving the Random Number Generator
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Contact Information
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-------------------------------------------------------------------------------
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Legal Notice
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TestFloat was written by John R. Hauser.
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THIS SOFTWARE IS DISTRIBUTED AS IS, FOR FREE. Although reasonable effort
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has been made to avoid it, THIS SOFTWARE MAY CONTAIN FAULTS THAT WILL AT
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TIMES RESULT IN INCORRECT BEHAVIOR. USE OF THIS SOFTWARE IS RESTRICTED TO
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PERSONS AND ORGANIZATIONS WHO CAN AND WILL TAKE FULL RESPONSIBILITY FOR ANY
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AND ALL LOSSES, COSTS, OR OTHER PROBLEMS ARISING FROM ITS USE.
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-------------------------------------------------------------------------------
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TestFloat Source Directory Structure
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Because TestFloat is targeted to multiple platforms, its source code
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is slightly scattered between target-specific and target-independent
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directories and files. The directory structure is as follows:
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processors
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testfloat
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templates
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386-Win32-gcc
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SPARC-Solaris-gcc
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The two topmost directories and their contents are:
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testfloat - Most of the source code needed for TestFloat.
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processors - Target-specific header files that are not specific to
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TestFloat.
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Within the `testfloat' directory are subdirectories for each of the
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targeted platforms. The TestFloat source code is distributed with targets
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`386-Win32-gcc' and `SPARC-Solaris-gcc' (and perhaps others) already
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prepared. These can be used as examples for porting to new targets. Source
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files that are not within these target-specific subdirectories are intended
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to be target-independent.
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The naming convention used for the target-specific directories is
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`<processor>-<executable-type>-<compiler>'. The names of the supplied
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target directories should be interpreted as follows:
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<processor>:
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386 - Intel 386-compatible processor.
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SPARC - SPARC processor (as used by Sun machines).
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<executable-type>:
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Win32 - Microsoft Win32 executable.
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Solaris - Sun Solaris executable.
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<compiler>:
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gcc - GNU C Compiler.
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You do not need to maintain this convention if you do not want to.
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Alongside the supplied target-specific directories there is a `templates'
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directory containing a set of ``generic'' target-specific source files.
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A new target directory can be created by copying the `templates' directory
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and editing the files inside. (Complete instructions for porting TestFloat
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to a new target are in the section _Steps_to_Creating_the_TestFloat_
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_Executables_.) Note that the `templates' directory will not work as a
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target directory without some editing. To avoid confusion, it would be wise
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to refrain from editing the files inside `templates' directly.
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In addition to the distributed sources, TestFloat depends on the existence
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of an appropriately-compiled SoftFloat binary and the corresponding header
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file `softfloat.h'. SoftFloat is not included with the TestFloat sources.
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It can be obtained from the Web page `http://HTTP.CS.Berkeley.EDU/~jhauser/
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arithmetic/SoftFloat.html'.
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As distributed, the makefiles for TestFloat assume the existence of three
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sibling directories:
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processors
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softfloat
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testfloat
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Only the `processors' and `testfloat' directories are included in the
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TestFloat package. The `softfloat' directory is assumed to contain a
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target-specific subdirectory within which the SoftFloat header file and
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compiled binary can be found. (See the source documentation accompanying
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SoftFloat.) The `processors' directory distributed with TestFloat is
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intended to be identical to that included with the SoftFloat source.
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These are the defaults, but other organizations of the sources are possible.
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The TestFloat makefiles and `milieu.h' files (see below) are easily edited
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to accommodate other arrangements.
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-------------------------------------------------------------------------------
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Target-Independent Modules
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The TestFloat program is composed of a number of modules, some target-
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specific and some target-independent. The target-independent modules are as
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follows:
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-- The `fail' module provides a common routine for writing an error message
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and aborting.
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-- The `random' module generates random integer values.
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-- The `writeHex' module defines routines for writing the various types in
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the hexadecimal form used by TestFloat.
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-- The `testCases' module generates test cases for the various types.
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-- The `testLoops' module contains various routines for exercising two
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implementations of a function and reporting any differences observed.
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-- The `slowfloat' module provides the simple floating-point implementation
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used by `testsoftfloat' for comparing against SoftFloat. The heart
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of `slowfloat' is found in either `slowfloat-32' or `slowfloat-64',
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depending on whether the `BITS64' macro is defined.
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-- The `systfloat' module gives a SoftFloat-like interface to the machine's
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floating-point.
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-- The `testFunction' module implements `testfloat's main loop for testing a
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function for all of the relevant rounding modes and rounding precisions.
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(The `testsoftfloat' program contains its own version of this code.)
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-- The `testfloat' and `testsoftfloat' modules are the main modules for the
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`testfloat' and `testsoftfloat' programs.
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Except possibly for `systfloat', these modules should not need to be
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modified.
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The `systfloat' module uses the floating-point operations of the C language
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to access a machine's floating-point. Unfortunately, some IEC/IEEE
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floating-point operations are not accessible within ISO/ANSI C. The
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following machine functions cannot be tested unless an alternate `systfloat'
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module is provided:
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<float>_to_int32 (rounded according to rounding mode)
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<float>_to_int64 (rounded according to rounding mode)
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<float>_round_to_int
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<float>_rem
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<float>_sqrt, except float64_sqrt
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<float>_eq_signaling
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<float>_le_quiet
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<float>_lt_quiet
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The `-list' option to `testfloat' will show the operations the program is
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prepared to test. The section _Target-Specific_Floating-Point_Subroutines_
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later in this document explains how to create a target-specific `systfloat'
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module to change the set of testable functions.
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-------------------------------------------------------------------------------
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Target-Specific Modules
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No target-specific modules are needed for `testsoftfloat'.
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The `testfloat' program uses two target-specific modules:
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-- The `systmodes' module defines functions for setting the modes
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controlling the system's floating-point, including the rounding mode and
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the rounding precision for extended double precision.
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-- The `systflags' module provides a function for clearing and examining the
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system's floating-point exception flags.
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These modules must be supplied for each target. They can be implemented in
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any way desired, so long as all is reflected in the target's makefile. For
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the targets that come with the distributed source, each of these modules is
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implemented as a single assembly language or C language source file.
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-------------------------------------------------------------------------------
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Target-Specific Header Files
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The purpose of the two target-specific header files is detailed below.
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In the following, the `*' symbol is used in place of the name of a specific
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target, such as `386-Win32-gcc' or `SPARC-Solaris-gcc', or in place of some
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other text as explained below.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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processors/*.h
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The target-specific `processors' header file defines integer types
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of various sizes, and also defines certain C preprocessor macros that
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characterize the target. The two examples supplied are `386-gcc.h' and
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`SPARC-gcc.h'. The naming convention used for processor header files is
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`<processor>-<compiler>.h'. The `processors' header file used to compile
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TestFloat should be the same as that used to compile SoftFloat.
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If 64-bit integers are supported by the compiler, the macro name `BITS64'
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should be defined here along with the corresponding 64-bit integer
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types. In addition, the function-like macro `LIT64' must be defined for
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constructing 64-bit integer literals (constants). The `LIT64' macro is used
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consistently in the TestFloat code to annotate 64-bit literals.
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If an inlining attribute (such as an `inline' keyword) is provided by the
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compiler, the macro `INLINE' should be defined to the appropriate keyword.
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If not, `INLINE' can be set to the keyword `static'. The `INLINE' macro
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appears in the TestFloat source code before every function that should be
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inlined by the compiler.
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For maximum flexibility, the TestFloat source files do not include the
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`processors' header file directly; rather, this file is included by the
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target-specific `milieu.h' header, and `milieu.h' is included by the source
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files.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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testfloat/*/milieu.h
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The `milieu.h' header file provides declarations that are needed to
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compile TestFloat. In particular, it is through this header file that
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the appropriate `processors' header is included to characterize the target
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processor. In addition, deviations from ISO/ANSI C by the compiler (such as
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names not properly declared in system header files) are corrected in this
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header if possible.
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If the preprocessor macro `BITS64' is defined in the `processors' header
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file but only the 32-bit version of SoftFloat is actually used, the `BITS64'
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macro should be undefined here after the `processors' header has defined it.
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If the C compiler implements the `long double' floating-point type of C
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as extended double precision, then `LONG_DOUBLE_IS_FLOATX80' should be
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defined here. Alternatively, if the C `long double' type is implemented as
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quadruple precision, `LONG_DOUBLE_IS_FLOAT128' should be defined. At most
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one of these macros should be defined. A C compiler is allowed to implement
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`long double' the same as `double', in which case neither of these macros
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should be defined.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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-------------------------------------------------------------------------------
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Target-Specific Floating-Point Subroutines
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This section applies only to `testfloat' and not to `testsoftfloat'.
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By default, TestFloat tests a machine's floating-point by testing the
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floating-point operations of the C language. Unfortunately, some IEC/IEEE
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floating-point operations are not defined within ISO/ANSI C. If a machine
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implements such ``non-C'' operations, target-specific subroutines for
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the operations can be supplied to allow TestFloat to test these machine
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features. Typically, such subroutines will need to be written in assembly
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language, although equivalent functions can sometimes be found among the
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system's software libraries.
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The following machine functions cannot be tested by TestFloat unless target-
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specific subroutines are supplied for them:
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<float>_to_int32 (rounded according to rounding mode)
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<float>_to_int64 (rounded according to rounding mode)
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<float>_round_to_int
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<float>_rem
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<float>_sqrt, except float64_sqrt
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<float>_eq_signaling
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<float>_le_quiet
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<float>_lt_quiet
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In addition to these, none of the `floatx80' functions can be tested by
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default if the C `long double' type is something other than extended double
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precision; and likewise, none of the `float128' functions can be tested by
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default if `long double' is not quadruple precision. Since `long double'
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cannot be both extended double precision and quadruple precision at the
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same time, at least one of these types cannot be tested by TestFloat without
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appropriate subroutines being supplied for that type. (On the other hand,
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few systems implement _both_ extended double-precision and quadruple-
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precision floating-point; and unless a system does implement both, it does
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not need both tested.)
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Note that the `-list' option to `testfloat' will show the operations
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TestFloat is prepared to test.
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TestFloat's `systfloat' module supplies the system version of the functions
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to be tested. The names of the `systfloat' subroutines are the same as the
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function names used as arguments to the `testfloat' command but with `syst_'
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prefixed--thus, for example, `syst_float32_add' and `syst_int32_to_float32'.
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The default `systfloat' module maps these system functions to the standard
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C operations; so `syst_float32_add', for example, is implemented using the
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C `+' operation for the single-precision `float' type. For each system
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function supplied by `systfloat', a corresponding `SYST_<function>'
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preprocessor macro is defined in `systfloat.h' to indicate that the function
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exists to be tested (e.g., `SYST_FLOAT32_ADD'). The `systfloat.h' header
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file also declares function prototypes for the `systfloat' functions.
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(The `systfloat.h' file that comes with the TestFloat package declares
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prototypes for all of the possible `systfloat' functions, whether defined in
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`systfloat' or not. There is no penalty for declaring a function prototype
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that is never used.)
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A target-specific version of the `systfloat' module can easily be created to
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replace the generic one. This in fact has been done for the example targets
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`386-Win32-gcc' and `SPARC-Solaris-gcc'. For each target, an assembly
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language `systfloat.S' has been created in the target directory along with
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a corresponding `systfloat.h' header file defining the `SYST_<function>'
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macros for the functions implemented. The makefiles of the targets have
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been edited to use these target-specific versions of `systfloat' rather than
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the generic one.
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The `systfloat' modules of the example targets have been written entirely
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in assembly language in order to bypass any peculiarities of the C compiler.
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Although this is probably a good idea, it is certainly not required.
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-------------------------------------------------------------------------------
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Steps to Creating the TestFloat Executables
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Porting and/or compiling TestFloat involves the following steps:
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1. Port SoftFloat and create a SoftFloat binary. (Refer to the
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documentation accompanying SoftFloat.)
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2. If one does not already exist, create an appropriate target-specific
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subdirectory under `testfloat' by copying the given `templates'
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directory. The remaining steps occur within the target-specific
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subdirectory.
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3. Edit the files `milieu.h' and `Makefile' to reflect the current
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environment.
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4. Make `testsoftfloat' by executing `make testsoftfloat' (or `make
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testsoftfloat.exe', or whatever the `testsoftfloat' executable is
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called). Verify that SoftFloat is working correctly by testing it with
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`testsoftfloat'.
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If you only wanted `testsoftfloat', you are done. The steps for `testfloat'
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continue:
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5. In the target-specific subdirectory, implement the `systmodes' and
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`systflags' modules. (The `syst_float_set_rounding_precision' function
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need not do anything if the system does not support extended double
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precision.)
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6. If the target machine supports standard floating-point functions that are
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not accessible within ISO/ANSI C, or if the C compiler cannot be trusted
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to use the machine's floating-point directly, create a target-specific
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`systfloat' module.
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7. In the target-specific subdirectory, execute `make'.
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-------------------------------------------------------------------------------
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Improving the Random Number Generator
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If you are serious about using TestFloat for testing floating-point, you
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should consider replacing the supplied `random.c' with a better target-
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specific one. The standard C `rand' function is rather poor on some
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systems, and consequently `random.c' has been written to assume very little
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about the quality of `rand'. As a result, the `rand' function is called
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more frequently than it might need to be, shortening the time before
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the random number generator repeats, and possibly wasting time as well.
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If `rand' is better on your system, or if another better random number
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generator is available (such as `rand48' on most Unix systems), TestFloat
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can be improved by overriding the given `random.c' with a target-specific
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one.
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-------------------------------------------------------------------------------
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Contact Information
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At the time of this writing, the most up-to-date information about
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TestFloat and the latest release can be found at the Web page `http://
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HTTP.CS.Berkeley.EDU/~jhauser/arithmetic/TestFloat.html'.
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