Berkeley TestFloat Release 3d: testsoftfloat

John R. Hauser
2017 August 18

Overview

The testsoftfloat program tests that a build of the Berkeley SoftFloat library conforms to the IEEE Standard for Binary Floating-Point Arithmetic as expected. Program testsoftfloat is part of the Berkeley TestFloat package, a small collection of programs for performing such tests. For general information about TestFloat, as well as for basics about the operation of testsoftfloat and how to interpret its output, see file TestFloat-general.html.

Note that, even if there are no bugs in the source code for SoftFloat (not guaranteed), a build of SoftFloat might still fail due to an issue with the build process, such as an incompatible compiler option or a compiler bug.

The testsoftfloat program will ordinarily test a function for all five rounding modes defined by the IEEE Floating-Point Standard, one after the other, plus possibly a sixth mode, round to odd (depending on the options selected when testsoftfloat was compiled). If an operation is not supposed to require rounding, it will by default be tested only with the rounding mode set to near_even (nearest/even). In the same way, if an operation is affected by the way in which underflow tininess is detected, testsoftfloat tests the function with tininess detected both before rounding and after rounding. For 80-bit double-extended-precision operations affected by rounding precision control, testsoftfloat also tests the function for all three rounding precision modes, one after the other. Testing can be limited to a single rounding mode, a single tininess mode, and/or a single rounding precision with appropriate command-line options.

Command Syntax

The testsoftfloat program is executed as a command with this syntax:

testsoftfloat [<option>...] <function>
Square brackets ([ ]) denote optional arguments, <option> is a supported option, and <function> is the name of either a testable function or a function set. The available options and function sets are documented below. If testsoftfloat is executed without any arguments, a summary of usage is written.

Options

The testsoftfloat program accepts several command options. If mutually contradictory options are given, the last one has priority.

-help

The -help option causes a summary of program usage to be written, after which the program exits.

-seed <num>

The -seed option sets the seed for the pseudo-random number generator used for generating test cases. The argument to -seed is a nonnegative integer. Executing the same testsoftfloat program with the same arguments (including the same pseudo-random number seed) should always perform the same sequence of tests, whereas changing the pseudo-random number seed should result in a different sequence of tests. The default seed number is 1.

-level <num>

The -level option sets the level of testing. The argument to -level can be either 1 or 2. The default is level 1. Level 2 performs many more tests than level 1 and thus can reveal bugs not found by level 1.

-errors <num>

The -errors option instructs testsoftfloat to report no more than the specified number of errors for any combination of function, rounding mode, etc. The argument to -errors must be a nonnegative decimal integer. Once the specified number of error reports has been generated, testsoftfloat ends the current test and begins the next one, if any. The default is -errors 20.

Against intuition, -errors 0 causes testsoftfloat to report every error it finds.

-errorstop

The -errorstop option causes the program to exit after the first function for which any errors are reported.

-forever

The -forever option causes a single function to be repeatedly tested. Only one rounding mode and/or rounding precision can be tested in a single execution. If not specified, the rounding mode defaults to nearest/even. For 80-bit double-extended-precision functions, the rounding precision defaults to full double-extended precision. The testing level is set to 2 by this option.

-precision32, -precision64, -precision80

For 80-bit double-extended-precision funcions affected by rounding precision control, the -precision32 option restricts testing to only the cases in which the rounding precision is 32 bits, equivalent to 32-bit single-precision. The other rounding precision choices are not tested. Likewise, -precision64 fixes the rounding precision to 64 bits, equivalent to 64-bit double-precision; and -precision80 fixes the rounding precision to the full 80 bits of the double-extended-precision format. All these options are ignored for operations not affected by rounding precision control.

-rnear_even, -rnear_maxMag, -rminMag, -rmin, -rmax, -rodd

The -rnear_even option restricts testing to only the cases in which the rounding mode is nearest/even. The other rounding mode choices are not tested. Likewise, -rnear_maxMag forces rounding to nearest/maximum magnitude (nearest-away), -rminMag forces rounding to minimum magnitude (toward zero), -rmin forces rounding to minimum (down, toward negative infinity), -rmax forces rounding to maximum (up, toward positive infinity), and -rodd, if supported, forces rounding to odd. These options are ignored for operations that are exact and thus do not round.

-tininessbefore, -tininessafter

The -tininessbefore option restricts testing to only the cases in which tininess on underflow is detected before rounding. Likewise, -tininessafter restricts testing to only the cases in which tininess on underflow is detected after rounding.

-notexact, -exact

For functions that round to an integer (conversions to integer types and the roundToInt functions), the -notexact option restricts testing to only the cases for which the exact operand (specifying whether the inexact exception flag may be raised) is false. Likewise, the -exact option restricts testing to only the cases for which the exact operand is true.

Function Sets

Just as testsoftfloat can test a function for all five or six rounding modes in sequence, multiple functions can be tested with a single execution of testsoftfloat. Two sets are recognized: -all1 and -all2. The set -all1 is all one-operand operations, while -all2 is all two-operand operations. A function set is used in place of a function name in the testsoftfloat command line, such as

testsoftfloat [<option>...] -all1

For the purpose of deciding the number of operands of an operation, any roundingMode and exact arguments are ignored. (Such arguments specify the rounding mode and whether the inexact exception flag may be raised, respectively.) Thus, functions that convert to integer type and the roundToInt functions are included in the set of one-operand operations tested by -all1.