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Rollup merge of #103456 - scottmcm:fix-unchecked-shifts, r=scottmcm

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`unchecked_{shl|shr}` should use `u32` as the RHS

The other shift methods, such as https://doc.rust-lang.org/nightly/std/primitive.u64.html#method.checked_shr and https://doc.rust-lang.org/nightly/std/primitive.i16.html#method.wrapping_shl, use `u32` for the shift amount.  That's consistent with other things, like `count_ones`, which also always use `u32` for a bit count, regardless of the size of the type.

This PR changes `unchecked_shl` and `unchecked_shr` to also use `u32` for the shift amount (rather than Self).

cc #85122, the `unchecked_math` tracking issue
This commit is contained in:
Manish Goregaokar 2022-11-18 17:48:17 -05:00 • committed by GitHub
commit e2301154e3
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5 changed files with 88 additions and 12 deletions
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16
library/core/src/num/int_macros.rs
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@ -761,10 +761,11 @@ macro_rules! int_impl {
#[rustc_const_unstable(feature = "const_inherent_unchecked_arith", issue = "85122")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn unchecked_shl(self, rhs: Self) -> Self {
pub const unsafe fn unchecked_shl(self, rhs: u32) -> Self {
// SAFETY: the caller must uphold the safety contract for
// `unchecked_shl`.
unsafe { intrinsics::unchecked_shl(self, rhs) }
// Any legal shift amount is losslessly representable in the self type.
unsafe { intrinsics::unchecked_shl(self, rhs.try_into().ok().unwrap_unchecked()) }
}
/// Checked shift right. Computes `self >> rhs`, returning `None` if `rhs` is
@ -808,10 +809,11 @@ macro_rules! int_impl {
#[rustc_const_unstable(feature = "const_inherent_unchecked_arith", issue = "85122")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn unchecked_shr(self, rhs: Self) -> Self {
pub const unsafe fn unchecked_shr(self, rhs: u32) -> Self {
// SAFETY: the caller must uphold the safety contract for
// `unchecked_shr`.
unsafe { intrinsics::unchecked_shr(self, rhs) }
// Any legal shift amount is losslessly representable in the self type.
unsafe { intrinsics::unchecked_shr(self, rhs.try_into().ok().unwrap_unchecked()) }
}
/// Checked absolute value. Computes `self.abs()`, returning `None` if
@ -1358,11 +1360,12 @@ macro_rules! int_impl {
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline(always)]
#[rustc_allow_const_fn_unstable(const_inherent_unchecked_arith)]
pub const fn wrapping_shl(self, rhs: u32) -> Self {
// SAFETY: the masking by the bitsize of the type ensures that we do not shift
// out of bounds
unsafe {
intrinsics::unchecked_shl(self, (rhs & ($BITS - 1)) as $SelfT)
self.unchecked_shl(rhs & ($BITS - 1))
}
}
@ -1387,11 +1390,12 @@ macro_rules! int_impl {
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline(always)]
#[rustc_allow_const_fn_unstable(const_inherent_unchecked_arith)]
pub const fn wrapping_shr(self, rhs: u32) -> Self {
// SAFETY: the masking by the bitsize of the type ensures that we do not shift
// out of bounds
unsafe {
intrinsics::unchecked_shr(self, (rhs & ($BITS - 1)) as $SelfT)
self.unchecked_shr(rhs & ($BITS - 1))
}
}