Auto merge of #132191 - Urgau:midpoint_signed_towards_zero, r=dtolnay · qinheping/verify-rust-std@c667683 (original) (raw)
`@@ -124,6 +124,37 @@ macro_rules! midpoint_impl {
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`((self ^ rhs) >> 1) + (self & rhs)
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`}
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`};
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($SelfT:ty, signed) => {
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/// Calculates the middle point of self and rhs.
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///
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/// midpoint(a, b) is (a + b) / 2 as if it were performed in a
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/// sufficiently-large signed integral type. This implies that the result is
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/// always rounded towards zero and that no overflow will ever occur.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(num_midpoint)]
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#[doc = concat!("assert_eq!(0", stringify!($SelfT), ".midpoint(4), 2);")]
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#[doc = concat!("assert_eq!((-1", stringify!($SelfT), ").midpoint(2), 0);")]
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#[doc = concat!("assert_eq!((-7", stringify!($SelfT), ").midpoint(0), -3);")]
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#[doc = concat!("assert_eq!(0", stringify!($SelfT), ".midpoint(-7), -3);")]
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#[doc = concat!("assert_eq!(0", stringify!($SelfT), ".midpoint(7), 3);")]
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/// ```
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#[unstable(feature = "num_midpoint", issue = "110840")]
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#[rustc_const_unstable(feature = "const_num_midpoint", issue = "110840")]
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#[must_use = "this returns the result of the operation, \
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without modifying the original"]
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#[inline]
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pub const fn midpoint(self, rhs: Self) -> Self {
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// Use the well known branchless algorithm from Hacker's Delight to compute
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// (a + b) / 2 without overflowing: ((a ^ b) >> 1) + (a & b).
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let t = ((self ^ rhs) >> 1) + (self & rhs);
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// Except that it fails for integers whose sum is an odd negative number as
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// their floor is one less than their average. So we adjust the result.
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t + (if t < 0 { 1 } else { 0 } & (self ^ rhs))
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}
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};
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`($SelfT:ty, $WideT:ty, unsigned) => {
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`` /// Calculates the middle point of self and rhs.
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`///
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`@@ -147,6 +178,32 @@ macro_rules! midpoint_impl {
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`((self as WideT+rhsasWideT + rhs as WideT+rhsasWideT) / 2) as $SelfT
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`}
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`};
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($SelfT:ty, $WideT:ty, signed) => {
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/// Calculates the middle point of self and rhs.
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///
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/// midpoint(a, b) is (a + b) / 2 as if it were performed in a
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/// sufficiently-large signed integral type. This implies that the result is
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/// always rounded towards zero and that no overflow will ever occur.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(num_midpoint)]
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#[doc = concat!("assert_eq!(0", stringify!($SelfT), ".midpoint(4), 2);")]
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#[doc = concat!("assert_eq!((-1", stringify!($SelfT), ").midpoint(2), 0);")]
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#[doc = concat!("assert_eq!((-7", stringify!($SelfT), ").midpoint(0), -3);")]
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#[doc = concat!("assert_eq!(0", stringify!($SelfT), ".midpoint(-7), -3);")]
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#[doc = concat!("assert_eq!(0", stringify!($SelfT), ".midpoint(7), 3);")]
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/// ```
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#[unstable(feature = "num_midpoint", issue = "110840")]
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#[rustc_const_unstable(feature = "const_num_midpoint", issue = "110840")]
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#[must_use = "this returns the result of the operation, \
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without modifying the original"]
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#[inline]
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pub const fn midpoint(self, rhs: SelfT)−>SelfT) -> SelfT)−>SelfT {
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((self as WideT+rhsasWideT + rhs as WideT+rhsasWideT) / 2) as $SelfT
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}
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};
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`}
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``
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`macro_rules! widening_impl {
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`@@ -300,6 +357,7 @@ impl i8 {
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` from_xe_bytes_doc = "",
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` bound_condition = "",
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`}
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midpoint_impl! { i8, i16, signed }
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`}
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``
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`impl i16 {
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` from_xe_bytes_doc = "",
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` bound_condition = "",
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`}
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midpoint_impl! { i16, i32, signed }
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`}
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``
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`impl i32 {
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`@@ -346,6 +405,7 @@ impl i32 {
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` from_xe_bytes_doc = "",
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` bound_condition = "",
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`}
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midpoint_impl! { i32, i64, signed }
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`}
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``
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`impl i64 {
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`@@ -369,6 +429,7 @@ impl i64 {
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` from_xe_bytes_doc = "",
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` bound_condition = "",
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`}
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midpoint_impl! { i64, i128, signed }
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`}
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``
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`impl i128 {
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`@@ -394,6 +455,7 @@ impl i128 {
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` from_xe_bytes_doc = "",
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` bound_condition = "",
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`}
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midpoint_impl! { i128, signed }
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`}
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``
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`#[cfg(target_pointer_width = "16")]
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`@@ -418,6 +480,7 @@ impl isize {
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` from_xe_bytes_doc = usize_isize_from_xe_bytes_doc!(),
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` bound_condition = " on 16-bit targets",
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`}
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midpoint_impl! { isize, i32, signed }
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`}
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`#[cfg(target_pointer_width = "32")]
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`@@ -442,6 +505,7 @@ impl isize {
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` from_xe_bytes_doc = usize_isize_from_xe_bytes_doc!(),
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` bound_condition = " on 32-bit targets",
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`}
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midpoint_impl! { isize, i64, signed }
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`}
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`#[cfg(target_pointer_width = "64")]
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`@@ -466,6 +530,7 @@ impl isize {
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` from_xe_bytes_doc = usize_isize_from_xe_bytes_doc!(),
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` bound_condition = " on 64-bit targets",
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`}
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midpoint_impl! { isize, i128, signed }
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`}
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`/// If the 6th bit is set ascii is lower case.
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