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init_expr.rs
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init_expr.rs
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//! Handling wasm constant values
use crate::emit::{Emit, EmitContext};
use crate::ir::Value;
use crate::parse::IndicesToIds;
use crate::{GlobalId, Result};
use anyhow::bail;
/// A constant which is produced in WebAssembly, typically used in global
/// initializers or element/data offsets.
#[derive(Debug, Copy, Clone)]
pub enum InitExpr {
/// An immediate constant value
Value(Value),
/// A constant value referenced by the global specified
Global(GlobalId),
}
impl InitExpr {
pub(crate) fn eval(init: &wasmparser::InitExpr, ids: &IndicesToIds) -> Result<InitExpr> {
use wasmparser::Operator::*;
let mut reader = init.get_operators_reader();
let val = match reader.read()? {
I32Const { value } => InitExpr::Value(Value::I32(value)),
I64Const { value } => InitExpr::Value(Value::I64(value)),
F32Const { value } => InitExpr::Value(Value::F32(f32::from_bits(value.bits()))),
F64Const { value } => InitExpr::Value(Value::F64(f64::from_bits(value.bits()))),
V128Const { value } => InitExpr::Value(Value::V128(v128_to_u128(&value))),
GlobalGet { global_index } => InitExpr::Global(ids.get_global(global_index)?),
_ => bail!("invalid constant expression"),
};
match reader.read()? {
End => {}
_ => bail!("invalid constant expression"),
}
reader.ensure_end()?;
Ok(val)
}
}
impl Emit for InitExpr {
fn emit(&self, cx: &mut EmitContext) {
match *self {
InitExpr::Value(val) => val.emit(&mut cx.encoder),
InitExpr::Global(id) => {
let idx = cx.indices.get_global_index(id);
cx.encoder.byte(0x23); // global.get
cx.encoder.u32(idx);
}
}
cx.encoder.byte(0x0b); // end
}
}
pub(crate) fn v128_to_u128(value: &wasmparser::V128) -> u128 {
let n = value.bytes();
((n[0] as u128) << 0)
| ((n[1] as u128) << 8)
| ((n[2] as u128) << 16)
| ((n[3] as u128) << 24)
| ((n[4] as u128) << 32)
| ((n[5] as u128) << 40)
| ((n[6] as u128) << 48)
| ((n[7] as u128) << 56)
| ((n[8] as u128) << 64)
| ((n[9] as u128) << 72)
| ((n[10] as u128) << 80)
| ((n[11] as u128) << 88)
| ((n[12] as u128) << 96)
| ((n[13] as u128) << 104)
| ((n[14] as u128) << 112)
| ((n[15] as u128) << 120)
}