testfloat_gen

# Berkeley TestFloat Release 3e: `testfloat_gen`

John R. Hauser
2018 January 20

## Overview

The `testfloat_gen` program generates test cases for testing that an implementation of floating-point arithmetic conforms to the IEEE Standard for Binary Floating-Point Arithmetic. `testfloat_gen` is part of the Berkeley TestFloat package, a small collection of programs for performing such tests. For general information about TestFloat, see file `TestFloat-general.html`.

A single execution of `testfloat_gen` generates test cases for only a single floating-point operation and associated options. The `testfloat_gen` program must be repeatedly executed to generate test cases for each operation to be tested.

The `testfloat_gen` program writes the test cases it generates to standard output. This output can either be captured in a file through redirection, or be piped to another program that exercises a floating-point operation using the test cases as they are supplied. Depending on use, the total output from `testfloat_gen` can be large, so piping to another program may be the best choice to avoid using inordinate file space. The format of `testfloat_gen`’s output is raw hexadecimal text, described in the section below titled Output Format.

## Command Syntax

The `testfloat_gen` program is executed as a command in one of these forms:

>     testfloat_gen [<option>...] <type>
>     testfloat_gen [<option>...] <function>

Square brackets (`[ ]`) denote optional arguments, and `<option>` is a supported option, documented below. A `testfloat_gen` command expects either a `<type>` specifying the type and number of outputs or a `<function>` naming a floating-point operation. If `testfloat_gen` is executed without any arguments, a summary of usage is written.

A `<type>` can be one of the following:

> `ui32` | unsigned 32-bit integers
> `ui64` | unsigned 64-bit integers
> `i32` | signed 32-bit integers
> `i64` | signed 64-bit integers
> `f16 [<num>]` | one or more 16-bit half-precision floating-point values
> `f32 [<num>]` | one or more 32-bit single-precision floating-point values
> `f64 [<num>]` | one or more 64-bit double-precision floating-point values
> `extF80 [<num>]` | one or more 80-bit double-extended-precision floating-point values
> `f128 [<num>]` | one or more 128-bit quadruple-precision floating-point values

Optional `<num>` is one of 1, 2, or 3. If a `<type>` is given without `<num>` (such as `ui32` or `f64`), `testfloat_gen` outputs a list of values of the specified type, one value per line, appropriate for testing a floating-point operation with exactly one operand of the given type. If a floating-point type and number are given (such as `f32` `2` or `extF80` `1`), `testfloat_gen` outputs the specified number of values per line, appropriate for testing a floating-point operation with that number of operands. Although the exact operation being tested is not specified, the test cases output by `testfloat_gen` cover all standard floating-point operations, to the degree explained in `TestFloat-general.html`.

If a `<function>` operation name is given, then each line of output from `testfloat_gen` contains not only the operands for that operation (as would be generated by an appropriate `<type>` argument) but also the expected results as determined by `testfloat_gen`’s internal floating-point emulation (Berkeley SoftFloat). The available operation names are listed in `TestFloat-general.html`. In all cases, floating-point operations have two results: first, a value, which may be floating-point, integer, or Boolean, and, second, the floating-point exception flags raised by the operation. If the output from a tested floating-point operation does not match the expected output specified by `testfloat_gen`, this may or may not indicate an error in the floating-point operation. For further explanation, see `TestFloat-general.html`, especially the section titled Variations Allowed by the IEEE Floating-Point Standard.

## Options

The `testfloat_gen` 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.

### `-prefix <text>`

The `-prefix` option causes `testfloat_gen` to write the supplied text argument verbatim as the first line of output before any test cases. This can be used, for example, to indicate to a downstream program what kind of test to perform for the test cases that follow.

### `-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 `testfloat_gen` program with the same arguments (including the same pseudo-random number seed) should always generate the same sequence of test cases, whereas changing the pseudo-random number seed should result in a different sequence of test cases. 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 causes many more test cases to be generated, with better coverage, than level 1.

### `-n <num>`

Option `-n` specifies the number of test cases to generate. For each `<type>` or `<function>` and each testing level (set by `-level`), there is a minimum value that `testfloat_gen` will accept for `<num>`. If no `-n` option is given, the number of test cases generated by `testfloat_gen` equals the minimum value acceptable for the `-n` argument. Option `-n` cannot be used to reduce this number, but can increase it, without changing the testing level.

### `-forever`

The `-forever` option causes test cases to be generated indefinitely, without limit (until the program is terminated by some external cause). The testing level is set to 2 by this option.

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

When a `<function>` is specified that is an 80-bit double-extended-precision operation affected by rounding precision control, the `-precision32` option sets the rounding precision to 32 bits, equivalent to 32-bit single-precision. Likewise, `-precision64` sets the rounding precision to 64 bits, equivalent to 64-bit double-precision, and `-precision80` sets 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. When rounding precision is applicable but not specified, the default is the full 80 bits, same as `-precision80`.

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

When a `<function>` is specified that requires rounding, the `-rnear_even` option sets the rounding mode to nearest/even; `-rnear_maxMag` sets rounding to nearest/maximum magnitude (nearest-away); `-rminMag` sets rounding to minimum magnitude (toward zero); `-rmin` sets rounding to minimum (down, toward negative infinity); `-rmax` sets rounding to maximum (up, toward positive infinity); and `-rodd`, if supported, sets rounding to odd. These options are ignored for operations that are exact and thus do not round. When rounding mode is relevant but not specified, the default is to round to nearest/even, same as `-rnear_even`.

### `-tininessbefore, -tininessafter`

When a `<function>` is specified that requires rounding, the `-tininessbefore` option indicates that tininess on underflow will be detected before rounding, while `-tininessafter` indicates that tininess on underflow will be detected after rounding. These options are ignored for operations that are exact and thus do not round. When the method of tininess detection matters but is not specified, the default is to detect tininess on underflow after rounding, same as `-tininessafter`.

### `-notexact, -exact`

When a `<function>` is specified that rounds to an integer (either conversion to an integer type or a `roundToInt` operation), the `-notexact` option indicates that the inexact exception flag is never raised, while `-exact` indicates that the inexact exception flag is to be raised if the result is inexact. For other operations, these options are ignored. If neither option is specified, the default is not to raise the inexact exception flag when rounding to an integer, same as `-notexact`.

## Output Format

For each test case generated, `testfloat_gen` writes a single line of text to standard output. When the `testfloat_gen` command is given a `<type>` argument, each test case consists of either one integer value or one, two, or three floating-point values. Each value is written to output as a raw hexadecimal number. When there is more than one value per line, they are separated by spaces. For example, output from executing

>     testfloat_gen f64 2

might look like this:

>     3F90EB5825D6851E C3E0080080000000
>     41E3C00000000000 C182024F8AE474A8
>     7FD80FFFFFFFFFFF 7FEFFFFFFFFFFF80
>     3FFFED6A25C534BE 3CA1000000020000
>     ...

with each hexadecimal number being one 64-bit floating-point value. Note that, for floating-point values, the sign and exponent are at the most-significant end of the number. Thus, for the first number on the first line above, the leading hexadecimal digits `3F9` are the sign and encoded exponent of the 64-bit floating-point value, and the remaining digits are the encoded significand.

When `testfloat_gen` is given a `<function>` operation name, each line of output has not only the operands for the operation but also the expected output, consisting of a result value and the exception flags that are raised. For example, the output from

>     testfloat_gen f64_add

could include these lines:

>     3F90EB5825D6851E C3E0080080000000 C3E0080080000000 01
>     41E3C00000000000 C182024F8AE474A8 41E377F6C1D46E2D 01
>     7FD80FFFFFFFFFFF 7FEFFFFFFFFFFF80 7FF0000000000000 05
>     3FFFED6A25C534BE 3CA1000000020000 3FFFED6A25C534BF 01
>     ...

On each line, the first two numbers are the operands for the floating-point addition, and the third and fourth numbers are the expected floating-point result (the sum) and the exception flags raised. Exception flags are encoded with one bit per flag as follows:

> bit 0`` | inexact exception
> bit 1 | underflow exception
> bit 2 | overflow exception
> bit 3 | infinite exception (“divide by zero”)
> bit 4 | invalid exception