Code Style
==========

This document is an incomplete description of the predominant style used in the
RISC-V Sail model.
Where something is not specified, please look for existing code similar to what
is being added and copy the predominant style.

For C and OCaml, the formatting rules should be followed where applicable.
For other languages, follow the standard style for that language if it exists;
for example, Python should follow the standard PEP-8 style.

Formatting
----------

* Block-level indentation uses two spaces

* There should be no trailing spaces on any lines

* All files should end with a newline character

* Unix-style line endings should be used

* Files should be free from leading, trailing and double blank lines

* There should be one space either side of operators such as `=` and `+`

* There should be no spaces before and one space after `,`

* There should be one space after control flow keywords such as `if`, `foreach`
  and `match`

* There should be no spaces between a function name and its arguments, for both
  definitions (valspecs, function definitions and function clauses) and calls,
  nor should there be any spaces immediately within the parentheses

* There should be no spaces between a vector and the opening square bracket for
  indexing or slicing, nor should there be any spaces immediately within the
  square brackets

* For large blocks of code with repetitive structure where it improves
  readability, additional whitespace may be inserted to align corresponding
  elements horizontally with each other, within reason

* Avoid unnecessary parentheses and curly braces unless doing so seriously
  hurts readability

* When modifying existing code that does not conform to this style, prefer
  matching the existing style

* Files should have suitable copyright headers.

Implementation
--------------

* Since this is the official model intended to be included as part of the
  RISC-V specifications, readability is paramount, including to those not
  already familiar with the details of that field of Computer Science (e.g.
  floating-point or cryptography)

* All instructions should be built as part of both the RV32 and RV64 models so
  as to provide a path to supporting mutable MXL/SXL/UXL; if necessary,
  constructs like `assert(sizeof(xlen) == 32)` at the start of the body can be
  used to suppress any type errors that arise as a result

* Avoid the use of hard-coded constants like 32 even if the instruction is
  RV32-specific, instead favouring `sizeof(xlen)` or a computed constant to
  more clearly express the underlying intent

* Local variables should be made immutable whenever possible, but short
  imperative loops with a small amount of local mutable state are preferred
  over less-readable functional-style recursive equivalents

* Choose carefully between integer and bitvector types, and avoid multiple
  round-trips between the two; for example, if counting something, use a `nat`
  and convert it to an appropriately-sized bitvector at the point it is stored
  in a register, but keep register source values as bitvectors until they are
  needed to be interpreted as integers (see the implementation of `MUL` as an
  example)

* Prefer `bool` over `bits(1)` when a value logically represents true or false
  rather than being a single bit with a numeric meaning, and vice-versa

* No new compile-time warnings from the Sail compiler should be introduced
  (this does not include C or OCaml warnings for the code generated by the Sail
  compiler)

* Do not use the `ext*` types and hooks for standard extensions unless
  providing a stub implementation; these are reserved for use by out-of-tree
  extensions that provide their own non-stub implementations
