FPCore 1.0

Syntax

The syntax is a simple S-expression syntax with the following grammar.

In this grammar, an FPCore term describes a single benchmark, with a set of free variables, a collection of metadata properties, and the floating-point expression defining the benchmark. White-space is ignored, and lines starting with the semicolon (;) are treated as comments and ignored. The basic tokens are defined as expected:

symbol

Any sequence of letters, digits, or characters from the set ~!@$%^&*_-+=<>.?/: not starting with a digit, implemented for ASCII by the regular expression:

[a-zA-Z~!@$%^&*_\-+=<>.?/:][a-zA-Z0-9~!@$%^&*_\-+=<>.?/:]*

number

An optional plus (+) or minus (-) sign followed by any sequence of digits. These may be optionally followed by a period (.) and another sequence of digits, which themselves may be optionally followed by an e, optional plus or minus sign, and a sequence of digits, implemented for ASCII by the regular expression:

[-+]?[0-9]+(\.[0-9]+)?(e[-+]?[0-9]+)?

string

Any sequence of printable characters, spaces, tabs, or carriage returns, delimited by double quotes ("). Within the double quotes, backslashes (\) have special meaning. A backslash followed by a double quote represents a double quote and does not terminate the string; a backslash followed by a backslash represents a backslash; other escapes may also be supported by implementations, but their meaning is not defined in this standard. We recommend that implementations only use escapes defined in the C or Matlab standard libraries. This definition is implemented for ASCII by the regular expression:

"([\x20-\x5b\x5d-\x7e]|\\["\\])+?"

Supported operations

The following operations are supported:

All operations have the same signature as the equivalent operations in C11. The arithmetic functions are all binary operators, except that unary - represents negation. The comparison operators and boolean and and or allow an arbitrary number of arguments.

A comparison operator with more than two operators is interpreted as the conjuction of all ordered pairs of arguments. In other words, == tests that all its arguments are equal; != tests that all its arguments are distinct; and <, >, <=, and >= test that their arguments are sorted (in the appropriate order), with equal elements allowed for <= and >=, and disallowed for < and >.

Following IEEE-754 and common C and Fortran implementations, FPCore does not prescribe an accuracy to any mathematical functions except the arithmetic operators, sqrt, and fma. If the exact accuracy is important, we recommend that benchmark users declare the implementation used with the :math-library property.

Supported constants

The following constants are supported:

The floating-point constants defined just like their analogs in GNU libc. All constants must evaluate to a value as close as possible to their mathematically-accurate real value.

Semantics

FPCore expressions can describe concrete floating-point computations, abstract specifications of those computations, or intermediates between the two. The semantics of FPCore are correspondingly flexible.

FPCore does not restrict the representation used to represent values when evaluating FPCore expressions. Numeric values can be floating point values of various precision, fixed point values, or (for abstract uses) mathematical reals, though individual FPCore expressions can use the :precision property to clarify what representation is expected. Evaluation nonetheless proceeds by fixed rules.

Expressions return either numeric values or boolean values. Operations that receive values of mixed or incorrect types, such as (+ 1 TRUE), are illegal and the results of evaluating them undefined.

Function application

The semantics of function application are standard.

if expressions

An if expression evaluates the conditional to a boolean and then returns the result of the first branch if the conditional is true or the second branch if the conditional is false.

let expressions

Bindings in a let expression are evaluated simultaneously, as in a simultaneous substitution. Thus, (let ([a b] [b a]) (- a b)) is the same as (- b a) and (let ([a 1] [b a]) b) is illegal unless a is available in the context. For sequentially binding variables, use nested lets.

while expressions

A while loop contains a conditional, a list of bound variables, and a return expression. Both the conditional and the return expression may refer to the bound variables. While loops are evaluated according the equality:

(while cond ([x init update] ...) body)
(let ([x init] ...)
  (if cond)
    (while cond ([x update update] ...) body)
    body)

In other words, the list of bound variables gives the variable's name, its initial value, and the value it is updated to after each iteration. The loop is executed by initializing all bound variables and then evaluating the condition and simultaneously updating the variables until the condition returns false. Once the condition returns false, the return expression is evaluated and its value is returned.