timesoftfloat

# Berkeley TestFloat Release 3e: `timesoftfloat`

John R. Hauser
2018 January 20

## Overview

The `timesoftfloat` program provides a simple way to evaluate the speed of the floating-point operations of the Berkeley SoftFloat library. Program `timesoftfloat` is included with the Berkeley TestFloat package, a small collection of programs for testing that an implementation of floating-point conforms to the IEEE Standard for Binary Floating-Point Arithmetic. Although `timesoftfloat` does not test floating-point correctness like the other TestFloat programs, nevertheless `timesoftfloat` is a partner to TestFloat’s `testsoftfloat` program. For more about TestFloat generally and `testsoftfloat` specifically, see file `TestFloat-general.html`.

Ordinarily, `timesoftfloat` will measure a function’s speed separately for each of the 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 `timesoftfloat` was compiled). If an operation is not supposed to require rounding, it will by default be timed 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, `timesoftfloat` times the function with tininess detected both before rounding and after rounding. For 80-bit double-extended-precision operations affected by rounding precision control, `timesoftfloat` also times the function for each of the three rounding precision modes, one after the other. Evaluation of a function can be limited to a single rounding mode, a single tininess mode, and/or a single rounding precision with appropriate command-line options.

For each function and mode evaluated, `timesoftfloat` reports the measured speed of the function in Mop/s, or “millions of operations per second”. The speeds reported by `timesoftfloat` may be affected somewhat by other software executing at the same time as `timesoftfloat`. Be aware also that the exact execution time of any SoftFloat function depends partly on the values of arguments and the state of the processor’s caches at the time the function is called. Your actual experience with SoftFloat may differ from the speeds reported by `timesoftfloat` for all these reasons.

Note that the remainder operations for larger formats (`f64_rem`, `extF80_rem`, and `f128_rem`) can be markedly slower than other operations, particularly for double-extended-precision (`extF80_rem`) and quadruple precision (`f128_rem`). This is inherent to the remainder operation itself and is not a failing of the SoftFloat implementation.

## Command Syntax

The `timesoftfloat` program is executed as a command with this syntax:

>     timesoftfloat [<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 `timesoftfloat` is executed without any arguments, a summary of usage is written.

## Options

The `timesoftfloat` 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.

### `-precision32, -precision64, -precision80`

For 80-bit double-extended-precision funcions affected by rounding precision control, the `-precision32` option restricts timing of an operation to only the cases in which the rounding precision is 32 bits, equivalent to 32-bit single-precision. Other rounding precision choices are not timed. 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 timing of an operation to only the cases in which the rounding mode is nearest/even. Other rounding mode choices are not timed. 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 timing of an operation to only the cases in which tininess on underflow is detected before rounding. Likewise, `-tininessafter` restricts measurement 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 timing of an operation 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 measurement to only the cases for which the `exact` operand is `true`.

## Function Sets

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

>     timesoftfloat [<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 timed by `-all1`.