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use crate::{BinaryReader, FromReader, Result, SectionLimited};
/// A reader for the `metadata.code.branch_hint` custom section.
pub type BranchHintSectionReader<'a> = SectionLimited<'a, BranchHintFunction<'a>>;
/// Branch hints for a single function.
///
/// Produced from [`BranchHintSectionReader`].
#[derive(Debug, Clone)]
pub struct BranchHintFunction<'a> {
/// The function that these branch hints apply to.
pub func: u32,
/// The branch hints available for this function.
pub hints: SectionLimited<'a, BranchHint>,
}
impl<'a> FromReader<'a> for BranchHintFunction<'a> {
fn from_reader(reader: &mut BinaryReader<'a>) -> Result<Self> {
let func = reader.read_var_u32()?;
// FIXME(#188) ideally wouldn't have to do skips here
let hints = reader.skip(|reader| {
let items_count = reader.read_var_u32()?;
for _ in 0..items_count {
reader.read::<BranchHint>()?;
}
Ok(())
})?;
Ok(BranchHintFunction {
func,
hints: SectionLimited::new(hints)?,
})
}
}
/// A hint for a single branch.
#[derive(Debug, Copy, Clone)]
pub struct BranchHint {
/// The byte offset, from the start of the function's body, of where the
/// hinted instruction lives.
pub func_offset: u32,
/// Whether or not the branch is hinted to be taken or not.
pub taken: bool,
}
impl<'a> FromReader<'a> for BranchHint {
fn from_reader(reader: &mut BinaryReader<'a>) -> Result<Self> {
let func_offset = reader.read_var_u32()?;
match reader.read_u8()? {
1 => {}
n => reader.invalid_leading_byte(n, "invalid branch hint byte")?,
}
let taken = match reader.read_u8()? {
0 => false,
1 => true,
n => reader.invalid_leading_byte(n, "invalid branch hint taken byte")?,
};
Ok(BranchHint { func_offset, taken })
}
}