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Improve some comments for non-zero ops

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This commit is contained in:
Maybe Waffle 2023-11-26 11:47:08 +00:00
parent 274b5249eb
commit c860ba1994
1 changed files with 44 additions and 14 deletions
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58
library/core/src/num/nonzero.rs
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@ -353,8 +353,13 @@ macro_rules! nonzero_unsigned_operations {
#[inline]
pub const fn checked_add(self, other: $Int) -> Option<$Ty> {
if let Some(result) = self.get().checked_add(other) {
// SAFETY: $Int::checked_add returns None on overflow
// so the result cannot be zero.
// SAFETY:
// - `checked_add` returns `None` on overflow
// - `self` and `other` are non-zero
// - the only way to get zero from an addition without overflow is for both
// sides to be zero
//
// So the result cannot be zero.
Some(unsafe { $Ty::new_unchecked(result) })
} else {
None
@ -386,8 +391,13 @@ macro_rules! nonzero_unsigned_operations {
without modifying the original"]
#[inline]
pub const fn saturating_add(self, other: $Int) -> $Ty {
// SAFETY: $Int::saturating_add returns $Int::MAX on overflow
// so the result cannot be zero.
// SAFETY:
// - `saturating_add` returns `u*::MAX` on overflow, which is non-zero
// - `self` and `other` are non-zero
// - the only way to get zero from an addition without overflow is for both
// sides to be zero
//
// So the result cannot be zero.
unsafe { $Ty::new_unchecked(self.get().saturating_add(other)) }
}
@ -1000,9 +1010,13 @@ macro_rules! nonzero_unsigned_signed_operations {
#[inline]
pub const fn checked_mul(self, other: $Ty) -> Option<$Ty> {
if let Some(result) = self.get().checked_mul(other.get()) {
// SAFETY: checked_mul returns None on overflow
// and `other` is also non-null
// so the result cannot be zero.
// SAFETY:
// - `checked_mul` returns `None` on overflow
// - `self` and `other` are non-zero
// - the only way to get zero from a multiplication without overflow is for one
// of the sides to be zero
//
// So the result cannot be zero.
Some(unsafe { $Ty::new_unchecked(result) })
} else {
None
@ -1034,9 +1048,14 @@ macro_rules! nonzero_unsigned_signed_operations {
without modifying the original"]
#[inline]
pub const fn saturating_mul(self, other: $Ty) -> $Ty {
// SAFETY: saturating_mul returns u*::MAX on overflow
// and `other` is also non-null
// so the result cannot be zero.
// SAFETY:
// - `saturating_mul` returns `u*::MAX`/`i*::MAX`/`i*::MIN` on overflow/underflow,
// all of which are non-zero
// - `self` and `other` are non-zero
// - the only way to get zero from a multiplication without overflow is for one
// of the sides to be zero
//
// So the result cannot be zero.
unsafe { $Ty::new_unchecked(self.get().saturating_mul(other.get())) }
}
@ -1107,8 +1126,13 @@ macro_rules! nonzero_unsigned_signed_operations {
#[inline]
pub const fn checked_pow(self, other: u32) -> Option<$Ty> {
if let Some(result) = self.get().checked_pow(other) {
// SAFETY: checked_pow returns None on overflow
// so the result cannot be zero.
// SAFETY:
// - `checked_pow` returns `None` on overflow/underflow
// - `self` is non-zero
// - the only way to get zero from an exponentiation without overflow is
// for base to be zero
//
// So the result cannot be zero.
Some(unsafe { $Ty::new_unchecked(result) })
} else {
None
@ -1149,8 +1173,14 @@ macro_rules! nonzero_unsigned_signed_operations {
without modifying the original"]
#[inline]
pub const fn saturating_pow(self, other: u32) -> $Ty {
// SAFETY: saturating_pow returns u*::MAX on overflow
// so the result cannot be zero.
// SAFETY:
// - `saturating_pow` returns `u*::MAX`/`i*::MAX`/`i*::MIN` on overflow/underflow,
// all of which are non-zero
// - `self` is non-zero
// - the only way to get zero from an exponentiation without overflow is
// for base to be zero
//
// So the result cannot be zero.
unsafe { $Ty::new_unchecked(self.get().saturating_pow(other)) }
}
}