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use crate::{encode_section, ConstExpr, Encode, Section, SectionId, ValType};
/// An encoder for the global section.
///
/// Global sections are only supported for modules.
///
/// # Example
///
/// ```
/// use wasm_encoder::{ConstExpr, Module, GlobalSection, GlobalType, Instruction, ValType};
///
/// let mut globals = GlobalSection::new();
/// globals.global(
/// GlobalType {
/// val_type: ValType::I32,
/// mutable: false,
/// shared: false,
/// },
/// &ConstExpr::i32_const(42),
/// );
///
/// let mut module = Module::new();
/// module.section(&globals);
///
/// let wasm_bytes = module.finish();
/// ```
#[derive(Clone, Default, Debug)]
pub struct GlobalSection {
bytes: Vec<u8>,
num_added: u32,
}
impl GlobalSection {
/// Create a new global section encoder.
pub fn new() -> Self {
Self::default()
}
/// The number of globals in the section.
pub fn len(&self) -> u32 {
self.num_added
}
/// Determines if the section is empty.
pub fn is_empty(&self) -> bool {
self.num_added == 0
}
/// Define a global.
pub fn global(&mut self, global_type: GlobalType, init_expr: &ConstExpr) -> &mut Self {
global_type.encode(&mut self.bytes);
init_expr.encode(&mut self.bytes);
self.num_added += 1;
self
}
/// Add a raw byte slice into this code section as a global.
pub fn raw(&mut self, data: &[u8]) -> &mut Self {
self.bytes.extend(data);
self.num_added += 1;
self
}
}
impl Encode for GlobalSection {
fn encode(&self, sink: &mut Vec<u8>) {
encode_section(sink, self.num_added, &self.bytes);
}
}
impl Section for GlobalSection {
fn id(&self) -> u8 {
SectionId::Global.into()
}
}
/// A global's type.
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
pub struct GlobalType {
/// This global's value type.
pub val_type: ValType,
/// Whether this global is mutable or not.
pub mutable: bool,
/// Whether this global is shared or not.
pub shared: bool,
}
impl Encode for GlobalType {
fn encode(&self, sink: &mut Vec<u8>) {
self.val_type.encode(sink);
let mut flag = 0;
if self.mutable {
flag |= 0b01;
}
if self.shared {
flag |= 0b10;
}
sink.push(flag);
}
}