Bitvector Literal

Overview

In the Sail ISA Specification Language, a bitvector literal is a lexical literal form that directly denotes a bitvector value of a specific width. Bitvector literals are part of Sail's general lit category, which appears in expressions (<exp>, <atomic_exp>), patterns (<pat>, <atomic_pat>), and atomic type contexts (<atomic_typ>).

Grammar Position

The <lit> non-terminal in the Sail grammar is the single production point at which bitvector literals are introduced. From the Sail grammar, <lit> is defined as:

<lit> ::= true
        | false
        | ()
        | NUMBER
        | undefined
        | bitzero
        | bitone
        | BINARY_LITERAL
        | HEXADECIMAL_LITERAL
        | STRING_LITERAL

Within this production, the members that denote bitvector values are:

• BINARY_LITERAL — a binary-formatted bitvector literal.
• HEXADECIMAL_LITERAL — a hexadecimal-formatted bitvector literal.
• bitzero — a named literal whose value is a bitvector consisting entirely of zero bits.
• bitone — a named literal whose value is a bitvector consisting entirely of one bits.

The two numeric literal forms (BINARY_LITERAL, HEXADECIMAL_LITERAL) provide explicit, width-carrying representations of bitvectors in source code, while bitzero and bitone provide convenient names for the all-zero and all-one bitvectors.

Occurrences in the Grammar

The <lit> production containing bitvector literals appears in several places in the Sail grammar:

• In atomic patterns (<atomic_pat>), allowing bitvector literals to be used as pattern matches.
• In atomic expressions (<atomic_exp>), allowing bitvector literals as values in expressions.
• In atomic types (<atomic_typ>), allowing bitvector literals to be used in type-level contexts.

These appearances mean bitvector literals can be written both as values and within pattern-matching positions during match expressions.

Related Concepts

• Sail ISA Specification Language — The language in which bitvector literals are defined.
• BNF Grammar — The grammar formalism used to specify the syntax of bitvector literals.

References

• Sail language specification (grammar excerpt).