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Fix an off-by-one modelling

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This commit is contained in:
Ayaz Hafiz 2022-11-01 22:42:52 -05:00
parent 63abc4096d
commit fc52e9582e
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GPG Key ID: 0E2A37416A25EF58
1 changed files with 6 additions and 15 deletions
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21
crates/compiler/mono/src/ir.rs
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@ -7390,31 +7390,22 @@ pub(crate) struct ListIndex(
impl ListIndex {
pub fn from_pattern_index(index: usize, arity: ListArity) -> Self {
match arity {
ListArity::Exact(_) => ListIndex::nth_head(index as _),
ListArity::Exact(_) => Self(index as _),
ListArity::Slice(head, tail) => {
if index < head {
ListIndex::nth_head(index as _)
Self(index as _)
} else {
// Slice(2, 6)
// Slice(head=2, tail=5)
//
// s t ... w y z x q
// 0 1 2 3 4 5 6 index
// 0 1 2 3 4 (index - head)
// 4 3 2 1 0 tail - (index - head)
ListIndex::nth_tail((tail - (index - head)) as _)
// 5 4 3 2 1 (tail - (index - head))
Self(-((tail - (index - head)) as i64))
}
}
}
}
fn nth_head(offset: u64) -> Self {
Self(offset as _)
}
fn nth_tail(offset: u64) -> Self {
let offset = offset as i64;
Self(-1 - offset)
}
}
pub(crate) type Store<'a> = (Symbol, Layout<'a>, Expr<'a>);
@ -7447,7 +7438,7 @@ pub(crate) fn build_list_index_probe<'a>(
arguments: env.arena.alloc([list_sym]),
});
let offset = (list_index + 1).abs();
let offset = list_index.abs();
let offset_sym = env.unique_symbol();
let offset_expr = Expr::Literal(Literal::Int((offset as i128).to_ne_bytes()));