Crate awint_macros

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Accompanying procedural macros to awint

Scope Dependencies

All of the macros often require Bits and InlAwi to be in scope. This could be from awint_core or be a reexport from awint. extawi! and similar always requires ExtAwi to be in scope, which could be imported from awint_ext or be a reexport from awint. cc! may require none, one, or both storage types depending on the input. Macros with fallible inputs require Option<T> variants to be in scope.

Inputs

Macros accepting only usize literals: inlawi_ty

Macros accepting only concatenations of components: inlawi, extawi

Macros accepting both: inlawi_zero, inlawi_umax, inlawi_imax, inlawi_imin, inlawi_uone, extawi_zero, extawi_umax, extawi_imax, extawi_imin, extawi_uone

The macros that accept both work by first trying to parse the whole input as a usize literal, then if the parsing fails attempt to interpret the input as concatenations of components.

Concatenations of Components

Some of the macros accept “concatenations of components”. A component can be a literal, a variable, or a filler. Components are written in a big endian order (like literals), and concatenations are written in a little endian order (because large concatentations will usually be formatted on different lines, and we want the data flow to be downwards), so the general layout of the input to a macro is:

macro!(
    ..., component 2, component 1, component 0; // concatenation 0
    ..., component 2, component 1, component 0; // concatenation 1
    ..., component 2, component 1, component 0; // concatenation 2
                            ⋮
)

The first concatenation, or concatenation 0, is the “source” concatenation, and the following concatenations are “sink” concatenations. Either statically at compile time or dynamically at run time, the macro will check if the concatenations all have the same bitwidths. If so, the corresponding bits from the source get copied to the corresponding bits of the sinks. The construction macros additionally return the source concatenation in a storage type such as InlAwi or ExtAwi. The sink concatenations are optional. If there is only a source concatenation, inlawi_ and extawi_ will just construct the value of the source, and cc_ will just perform bounds checks.

These macros automate a large number of things for the user:

  • Using only const capable constructions and functions if possible
  • All bounds checks are run before any fielding happens, so that no mutation or allocation occurs when an error is returned, matching the common behavior of functions in the awint system.
  • Trying to optimize away as many bounds checks as possible
  • Trying to optimize away intermediate buffers
  • Concatenating literals together at compile time, and even returning infallibly if possible
  • Trying to use the most efficient copying method

Before going into detail on each component type, we will first explain all the error conditions for the index bounds checks. Even though cc_ macros with only a source concatenation do no construction or copying, they are useful for bounds checks. Here, we pass the simplest variable input to the cc! macro, a single concatenation with a single component.

use awint::prelude::*;

let x = ExtAwi::zero(bw(10));
let r0 = 2;
let r1 = 8;
let r2 = 20;

// The input is just the variable `x`. The macro is able to determine that
// no bounds checks are needed, so it returns `()`.
assert_eq!(cc!(x), ());

// This component is the variable `x` indexed with the bit range `r0..r1`.
// The bounds checks succeed, so the macro returns `Some(())`.
assert!(cc!(x[r0..r1]).is_some());

// We could also use a static range. We call it "static" because the macro
// is able to know the value of the range at compile time.
assert!(cc!(x[2..8]).is_some());

// The first kind of invalid bound is a reversed range, in which the
// start of the range is larger than the end of the range.
assert!(cc!(x[r1..r0]).is_none());

// Here, the macro is able to determine at compile time that the range is
// reversed
//cc!(x[8..2]); // error: ... has a reversed range

// The second kind of invalid bound is a range that extends beyond the
// width of the variable or literal. Earlier, the values of 2 and 8 were
// less than or equal to `x.bw()`, so the check succeeded. Here the value
// of 20 causes the macro to return `None`.
assert!(cc!(x[r0..r2]).is_none());

// Note: the widths of concatenations can be zero for the `cc_` macros.
// Static zero width ranges will cause a compile-time panic as a warning
// about components that do nothing, but they are achievable with dynamic
// ranges.
let r = 5;
assert!(cc!(x[r..r]).is_some());
let r = 10;
assert!(cc!(x[r..r]).is_some());
// The restriction about values not being larger than `x.bw()` still
// applies.
let r = 11;
assert!(cc!(x[r..r]).is_none());

// `InlAwi`s and `ExtAwi`s cannot have zero bitwidths, so zero width
// concatenations will cause their macros to panic at compile time or
// return `None`.
let r = 5;
assert!(extawi!(x[r..r]).is_none());
// error: determined statically that this has zero bitwidth
//let _ = inlawi!(x[5..5]);

// The third error condition occurs when concatenation bitwidths are
// unequal, but first we need to go into more detail on the component
// types.

Literals

When the parser sees that the first character of a component is ‘-’ or ‘0’..=‘9’, and it isn’t part of a lone range, it will assume the component is a literal and pass it to the FromStr implementation of ExtAwi. See that documentation for more details.

Note: The FromStr implementation allows for signed and unsigned values, binary, octal, decimal, and hexadecimal bases, but for the remainder of this documentation we will mainly be using unsigned hexadecimal. This is because it neatly divides along bit multiples of 4, and the large base allows one to easily see where different groups of 4 bits are being copied.

use awint::prelude::*;

// Here, we pass a single concatenation of 3 literals to the `inlawi!`
// construction macro. constructs an `InlAwi` out of a 4 bit signed
// negative 1, a 16 bit binary string, and a 8 bit unsigned 42. The
// total bitwidth is 4 + 16 + 8 = 28.
let awi: inlawi_ty!(28) = inlawi!(-1i4, 0000_0101_0011_1001, 42u8);
assert_eq!(awi, inlawi!(1111_0000010100111001_00101010));

// Literals can have static ranges applied to them, which might be useful
// in some circumstances for readability.
assert_eq!(inlawi!(0x654321_u24[4..16]), inlawi!(0x432_u12));

// Arbitrary dynamic ranges using things from outside the macro can also
// be applied. The macros will assume the range bounds to result in `usize`.
let x: usize = 8;
let awi = ExtAwi::zero(bw(12));
// At runtime, `x` evaluates to 8 and `x + awi.bw()` evaluates to 20
assert_eq!(
    extawi!(0x98765_u20[x..(x + awi.bw())]).unwrap(),
    extawi!(0x987u12)
);

Variables

Anything that has well defined bw() -> usize, const_as_ref() -> &Bits, and const_as_mut() -> &mut Bits functions can be used as a variable. Arbitrary Bits references (Bits itself has these functions, they are just hidden from the documentation), ExtAwi, InlAwi, and other well defined arbitrary width integer types can thus be used as variables.

use awint::prelude::*;

let source = inlawi!(0xc4di64);
// a bunch of zeroed 64 bit arbitrary width integers from different
// storage types and construction methods.
let mut awi = ExtAwi::zero(bw(64));
let a = awi.const_as_mut();
let mut b = extawi!(0i64);
let mut c = <inlawi_ty!(64)>::zero();

// Use the `cc` macro to copy the source concatenation `source` to the sink
// concatenations `a`, `b`, and `c`. Here, every concatenation is just a
// single variable component.
cc!(source; a; b; c).unwrap();

assert_eq!(a, inlawi!(0xc4di64).const_as_ref());
assert_eq!(b, extawi!(0xc4di64));
assert_eq!(c, inlawi!(0xc4di64));

let awi = inlawi!(0xau4);
let a = awi.const_as_ref();
let b = extawi!(0xbu4);
let c = inlawi!(0xcu4);

// Use `extawi` to infallibly concatenate variables together. Here, there
// is only one concatenation with multiple variable components.
assert_eq!(extawi!(a, b, c), extawi!(0xabcu12));

Now that we have both literals and variables, we can demonstrate more complicated interactions. In case it still isn’t clear what the “corresponding copying” means, here we have a source concatenation of 4 components each with 3 hexadecimal digits being copied onto a sink concatenation of 3 components each with 4 hexadecimal digits.

use awint::prelude::*;

let y3 = inlawi!(0xba9u12);
let y2 = inlawi!(0x876u12);
let y1 = inlawi!(0x543u12);
let y0 = inlawi!(0x210u12);

let mut z2 = inlawi!(0u16);
let mut z1 = inlawi!(0u16);
let mut z0 = inlawi!(0u16);

cc!(
    y3, y2, y1, y0;
    z2, z1, z0;
).unwrap();

assert_eq!(z2, inlawi!(0xba98u16));
assert_eq!(z1, inlawi!(0x7654u16));
assert_eq!(z0, inlawi!(0x3210u16));

Visually, the components in the two concatenations are being aligned like this:

|-----y3----|-----y2----|-----y1----|-----y0----|
| b   a   9 | 8   7   6 | 5   4   3 | 2   1   0 |
| b   a   9   8 | 7   6   5   4 | 3   2   1   0 |
|-------z2------|-------z1------|-------z0------|

Again, arbitrary ranges can be applied to variables:

use awint::prelude::*;

let mut a = inlawi!(0x9876543210u40);

let b = extawi!(
    a[..=7], a[(a.bw() - 16)..];
    a[(5 * 4)..(9 * 4)], a[..(2 * 4)];
).unwrap();
assert_eq!(a, inlawi!(0x9109843276u40));
assert_eq!(b, extawi!(0x109876_u24));

Fillers

The third type of component is written as a range with no variable or literal attached. When used in sources, corresponding sink bits are left unmutated. When used in sinks, corresponding source bits have no effect.

When used in the source bits of specified initialization construction macros (inlawi_zero!, extawi_zero, inlawi_umax!, etc), fillers adopt what the corresponding bits would be normally initialized to (zero, unsigned maximum value, etc).

The unspecified initialization macros inlawi! and extawi! do not allow fillers in their source concatenations, because it would be ambiguous what those bits should initially be set to.

use awint::prelude::*;

let x = inlawi!(0x1234u16);
let mut y = inlawi!(0x5678u16);

// note: because the range bounds cannot be negative, ranges starting
// with 0 (e.x. `0..r`) can have the zero omitted and just use `..r`.
cc!(
    x, ..8;
    ..8, y;
).unwrap();

assert_eq!(y, inlawi!(0x3478u16));

The ..8 filler in the source aligned with the two digits 0x78u8 in the y component in the sink, so they were left unmutated. The digits 0x34u8 in the source aligned with and overwrote 0x56u8 in the sink. The 0x12u8 aligned with the ..8 filler in the sink, so they did nothing.

Fillers are also useful in cases where all concatenations lack a needed degree of determinable width, and we want a cheap way to specify it:

use awint::prelude::*;

let x = extawi!(-99i44);

// error: `InlAwi` construction macros need at least one concatenation to
// have a width that can be determined statically by the macro
//inlawi!(x);

assert_eq!(inlawi!(x; ..44).unwrap(), inlawi!(-99i44));

// error: there is a only a source concatenation that has no statically
// or dynamically determinable width
//extawi_umax!(.., x);

let r = 128;
assert_eq!(extawi_umax!(.., x; ..r).unwrap(), extawi!(-99i128));

Unbounded fillers

Unbounded fillers can be thought as dynamically resizing fillers that try to expand until the bitwidths of different concatenations match. To understand how unbounded fillers interact, consider these three cases:

use awint::prelude::*;

// This first case has no fillers in the first concatenation, so the filler
// in the second concatenation will expand to be of bitwidth `12 - y.bw()`.

let mut y = extawi!(0u8);
cc!(
    0x321u12;
    .., y;
).unwrap();
assert_eq!(y, extawi!(0x21u8));

// Do the same call again, but with `y.bw() == 4`
let mut y = extawi!(0u4);
cc!(
    0x321u12;
    .., y;
).unwrap();
assert_eq!(y, extawi!(0x1u4));

// The 12 bits of the first concatenation cannot correspond with
// the minimum 16 bits of the second, so this call returns `None`.
let mut y = extawi!(0u16);
assert!(cc!(0x321u12; .., y).is_none());

// This second case ends up enforcing that `y.bw()` is at least 12. The 12
// bits of the literal always get copied to the least significant bits of
// `y`.

let mut y = extawi!(0u20);
cc!(
    .., 0x321u12;
    y;
).unwrap();
assert_eq!(y, extawi!(0x00321u20));

let mut y = extawi_umax!(32);
cc!(
    .., 0x321u12;
    y;
).unwrap();
assert_eq!(y, extawi!(0xffff_f321_u32));

let mut y = extawi_umax!(8);
assert!(cc!(.., 0x321u12; y).is_none());

// The third case allows `y.bw()` to be any possible bitwidth. If
// `y.bw() < 12` it will act like the first case, otherwise it acts like the
// second case. Because there are no restrictions on concatenation widths
// and there are no ranges that could index the variables out of bounds,
// these calls are infallible and no `Option` is returned.

let mut y = extawi!(0u20);
cc!(
    .., 0x321u12;
    .., y;
);
assert_eq!(y, extawi!(0x00321u20));

let mut y = extawi!(0u4);
cc!(
    .., 0x321u12;
    .., y;
);
assert_eq!(y, extawi!(0x1u4));

// Unbounded fillers are also allowed in less significant positions, in
// which case alignment of the components occurs starting from the most
// significant bit.

let mut y = extawi!(0u20);
cc!(
    0x321u12, ..;
    y, ..;
);
assert_eq!(y, extawi!(0x32100u20));

// The macros are even smart enough to do this:

let mut y = extawi_umax!(24);
cc!(0x3u4, .., 0x21u8; y).unwrap();
assert_eq!(y, extawi!(0x3fff21u24));

// Note again that filler widths cannot be negative, and so this will cause
// an error because we are trying to compress the 4 bit and 8 bit components
// into a less than 12 bit space.

let mut y = extawi!(0u8);
assert!(cc!(0x3u4, .., 0x21u8; y).is_none());

Only one unbounded filler per concatenation is allowed. Consider this case, in which it would be ambiguous about how the middle component should be aligned.

cc!(
    .., 0x321u12, ..;
    y;
); // Error: there is more than one unbounded filler

Additionally, multiple concatenations with unbounded fillers must all have their fillers aligned to the same end or have a concatenation without an unbounded filler.

// all allowed:
cc!(
    .., x;
    .., y;
    .., z;
);
cc!(
    x, ..;
    y, ..;
    z, ..;
);
// allowed, because the macro can infer the alignment by using the bitwidth
// of `var`
cc!(
    .., x;
    y, .., z;
    a, ..;
    var;
);
// disallowed, because the overlaps are ambiguous:
cc!(
    .., x;
    y, ..;
);
cc!(
    a, .., x;
    b, .., y;
    c, .., z;
);

It is technically possible to infer that ambiguous overlap could not occur in this case, but this is still disallowed by the macro, and it is more readable to just split the macro into two for both alignments.

cc!(
    0x4567u16, .., 0x123u12;
    y0[..4], .., y1[..4];
);
// the above macro is semantically equivalent to these two macros combined:
cc!(
    0x4567u16, ..;
    y0[..4], ..;
);
cc!(
    .., 0x123u12;
    .., y1[..4];
);

Other Notes

  • If dynamic values are used in ranges, they should not use generator like behavior (e.x. using a function that changes its output between calls in x[f()..=f()]), or else you may get unexpected behavior. The parser and code generator treats identical strings like they produce the same value every time, and would call f() only once.
  • In general, the macros use the Bits::field operation to copy different bitfields independently to a buffer, then field from the buffer to the sink components. When concatenations take the form variable or constant with full range; var_1[..]; var_2[..]; var_3[..], ..., the macros use Bits::copy_assign to directly copy without an intermediate buffer. This copy assigning mode cannot copy between Bits references that point to the same underlying storage, because it results in aliasing. Thus, trying to do something like cc!(x; x) results in the borrow checker complaining about macro generated variables within the macro being borrowed as both immutable and mutable. cc!(x; x) is semantically a no-op anyway, so it should not be used.
  • The code generated by the macros takes special care to avoid panicking or overflowing. If a range is reversed (the start value is larger than the end value), the macro will will return a compile time error or None at runtime before trying to calculate something like end - start. The only way to overflow is to exceed usize::MAX in concatenation widths, or the individual arbitrary expressions entered into the macro overflow (e.x. ..(usize::MAX + 1)).
  • Under some conditions, warnings about unused Option<()>s are not produced from procedural macros. If a fallible macro is called without appending .unwrap() or otherwise handling the Option, it will silently do nothing if None is returned.
  • The macros have to be unsanitized to support using arbitrary variables and ranges. It is still very hard to escape the scoping by some kind of injection, because all arbitrary values are individually assigned to a let _: usize = ...; statement, all variable names are individually referenced like let _: &Bits = (...).const_as_ref();, and all semicolons are eliminated early in the parsing process. Only obviously bad inputs using things such as multiple unmatched parenthesis, other specially designed macros, or fake structs could cause compiling broken checks or problems that extend beyond the immediate scope of the macro.
  • In case you want to see the code generated by a macro, you can use the awint_macro_internals::code_gen function and call it with the same arguments as the respective macro in awint_macros/src/lib.rs.

Macros

cc

Copy Corresponding Concatenations of Components Dynamically. Takes concatenations of components as an input, and copies bits of the source to corresponding bits of the sinks. Returns nothing if the operation is infallible, otherwise returns Option<()>. Returns None if component indexes are out of bounds or if concatenation bitwidths mismatch. Performs allocation in general, but will try to avoid allocation if the common bitwdith can be determined statically, or if concatenations are all of single components. See the documentation of awint_macros for more.

cc_imax

The same as cc! but with Signed-maximum-value specified initialization.

cc_imin

The same as cc! but with Signed-minimum-value specified initialization.

cc_umax

The same as cc! but with Unsigned-maximum-value specified initialization.

cc_uone

The same as cc! but with Unsigned-one-value specified initialization.

cc_zero

The same as cc! but with Zero-value specified initialization.

extawi

Takes concatenations of components as an input, and copies bits of the source to corresponding bits of the sinks. The source value is also used to construct an ExtAwi. The common width must be dynamically determinable by the macro (e.g. not all concatenations can have unbounded fillers), and the source cannot contain fillers. Returns a plain ExtAwi if infallible from what the macro can statically determine, otherwise returns Option<ExtAwi>. Returns None if component indexes are invalid or if concatenation bitwidths mismatch. See the documentation of awint_macros for more.

extawi_imax

The same as extawi! but with Signed-maximum-value specified initialization.

extawi_imin

The same as extawi! but with Signed-minimum-value specified initialization.

extawi_umax

The same as extawi! but with Unsigned-maximum-value specified initialization.

extawi_uone

The same as extawi! but with Unsigned-one-value specified initialization.

extawi_zero

The same as extawi! but with Zero-value specified initialization.

inlawi

Takes concatenations of components as an input, and copies bits of the source to corresponding bits of the sinks. The source value is also used to construct an InlAwi. The common width must be statically determinable by the macro (e.g. at least one concatenation must have only literal ranges), and the source cannot contain fillers. Returns a plain InlAwi if infallible from what the macro can statically determine, otherwise returns Option<InlAwi>. Returns None if component indexes are invalid or if concatenation bitwidths mismatch. See the documentation of awint_macros for more.

inlawi_imax

The same as inlawi! but with Signed-maximum-value specified initialization.

inlawi_imin

The same as inlawi! but with Signed-minimum-value specified initialization.

inlawi_ty

Specifies an InlAwi type in terms of its bitwidth as a usize literal.

inlawi_umax

The same as inlawi! but with Unsigned-maximum-value specified initialization.

inlawi_uone

The same as inlawi! but with Unsigned-one-value specified initialization.

inlawi_zero

The same as inlawi! but with Zero-value specified initialization.