Struct VmData 

pub struct VmData<const N: usize = { u8::MAX as usize }> {
    pub vars: Arc<VarMap>,
    /* private fields */
}

A flattened math expression, ready for evaluation or further compilation.

Under the hood, VmData stores two different representations:

• A tape in single static assignment form (SsaTape), which is suitable for use during tape simplification
• A tape in register-allocated form (RegTape), which can be efficiently evaluated or lowered into machine assembly

Example

Consider the expression x + y. The SSA tape will look something like this:

$0 = INPUT 0   // X
$1 = INPUT 1   // Y
$2 = ADD $0 $1 // (X + Y)

This will be lowered into a tape using real (or VM) registers:

r0 = INPUT 0 // X
r1 = INPUT 1 // Y
r0 = ADD r0 r1 // (X + Y)

Note that in this form, registers are reused (e.g. r0 stores both X and X + Y).

We can peek at the internals and see this register-allocated tape:

use fidget_core::{
    compiler::RegOp,
    context::{Context, Tree},
    vm::VmData,
    var::Var,
};

let tree = Tree::x() + Tree::y();
let mut ctx = Context::new();
let sum = ctx.import(&tree);
let data = VmData::<255>::new(&ctx, &[sum])?;
assert_eq!(data.len(), 4); // X, Y, (X + Y), and output

let mut iter = data.iter_asm();
let vars = &data.vars; // map from var to index
assert_eq!(iter.next().unwrap(), RegOp::Input(0, vars[&Var::X] as u32));
assert_eq!(iter.next().unwrap(), RegOp::Input(1, vars[&Var::Y] as u32));
assert_eq!(iter.next().unwrap(), RegOp::AddRegReg(0, 0, 1));

Despite this peek at its internals, users are unlikely to touch VmData directly; a VmShape wraps the VmData and implements our common traits.

Fields

vars: Arc<VarMap>

Mapping from variables to indices during evaluation

This member is stored in a shared pointer because it’s passed down to children (constructed with VmData::simplify).

Implementations

impl<const N: usize> VmData<N>

pub fn new(context: &Context, nodes: &[Node]) -> Result<Self, Error>

Builds a new tape for the given node

pub fn len(&self) -> usize

Returns the length of the internal VM tape

pub fn is_empty(&self) -> bool

Returns true if the internal VM tape is empty

pub fn choice_count(&self) -> usize

Returns the number of choice (min/max) nodes in the tape.

This is required because some evaluators pre-allocate spaces for the choice array.

pub fn output_count(&self) -> usize

Returns the number of output nodes in the tape.

This is required because some evaluators pre-allocate spaces for the output array.

pub fn slot_count(&self) -> usize

Returns the number of slots used by the inner VM tape

pub fn simplify<const M: usize>( &self, choices: &[Choice], workspace: &mut VmWorkspace<M>, tape: VmData<M>, ) -> Result<VmData<M>, Error>

Simplifies both inner tapes, using the provided choice array

To minimize allocations, this function takes a VmWorkspace and spare VmData; it will reuse those allocations.

pub fn iter_asm(&self) -> impl Iterator<Item = RegOp> + '_

Produces an iterator that visits RegOp values in evaluation order

pub fn pretty_print(&self)

Pretty-prints the inner SSA tape

Trait Implementations

impl<const N: usize> Default for VmData<N>

fn default() -> VmData<N>

Returns the “default value” for a type.

impl<'de, const N: usize> Deserialize<'de> for VmData<N>

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<const N: usize> From<VmData<N>> for GenericVmFunction<N>

fn from(d: VmData<N>) -> Self

Converts to this type from the input type.

impl<const N: usize> Serialize for VmData<N>

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.