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use clippy_utils::diagnostics::span_lint;
use clippy_utils::ty::is_isize_or_usize;
use rustc_hir::Expr;
use rustc_lint::LateContext;
use rustc_middle::ty::{self, FloatTy, Ty};
use super::{utils, CAST_PRECISION_LOSS};
pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
if !cast_from.is_integral() || cast_to.is_integral() {
return;
}
let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
let to_nbits = if cast_to.kind() == &ty::Float(FloatTy::F32) {
32
} else {
64
};
if !(is_isize_or_usize(cast_from) || from_nbits >= to_nbits) {
return;
}
let cast_to_f64 = to_nbits == 64;
let mantissa_nbits = if cast_to_f64 { 52 } else { 23 };
let arch_dependent = is_isize_or_usize(cast_from) && cast_to_f64;
let arch_dependent_str = "on targets with 64-bit wide pointers ";
let from_nbits_str = if arch_dependent {
"64".to_owned()
} else if is_isize_or_usize(cast_from) {
"32 or 64".to_owned()
} else {
utils::int_ty_to_nbits(cast_from, cx.tcx).to_string()
};
span_lint(
cx,
CAST_PRECISION_LOSS,
expr.span,
&format!(
"casting `{0}` to `{1}` causes a loss of precision {2}(`{0}` is {3} bits wide, \
but `{1}`'s mantissa is only {4} bits wide)",
cast_from,
if cast_to_f64 { "f64" } else { "f32" },
if arch_dependent { arch_dependent_str } else { "" },
from_nbits_str,
mantissa_nbits
),
);
}
|
