Rollup merge of #140172 - bjoernager:const-float-algebraic, r=RalfJung

Make algebraic functions into `const fn` items.

Tracking issue: #136469

This PR makes the algebraic intrinsics and the unstable, algebraic functions of `f16`, `f32`, `f64`, and `f128` into `const fn` items:

```rust
impl f16 {
    pub const fn algebraic_add(self, rhs: f16) -> f16;
    pub const fn algebraic_sub(self, rhs: f16) -> f16;
    pub const fn algebraic_mul(self, rhs: f16) -> f16;
    pub const fn algebraic_div(self, rhs: f16) -> f16;
    pub const fn algebraic_rem(self, rhs: f16) -> f16;
}

impl f32 {
    pub const fn algebraic_add(self, rhs: f32) -> f32;
    pub const fn algebraic_sub(self, rhs: f32) -> f32;
    pub const fn algebraic_mul(self, rhs: f32) -> f32;
    pub const fn algebraic_div(self, rhs: f32) -> f32;
    pub const fn algebraic_rem(self, rhs: f32) -> f32;
}

impl f64 {
    pub const fn algebraic_add(self, rhs: f64) -> f64;
    pub const fn algebraic_sub(self, rhs: f64) -> f64;
    pub const fn algebraic_mul(self, rhs: f64) -> f64;
    pub const fn algebraic_div(self, rhs: f64) -> f64;
    pub const fn algebraic_rem(self, rhs: f64) -> f64;
}

impl f128 {
    pub const fn algebraic_add(self, rhs: f128) -> f128;
    pub const fn algebraic_sub(self, rhs: f128) -> f128;
    pub const fn algebraic_mul(self, rhs: f128) -> f128;
    pub const fn algebraic_div(self, rhs: f128) -> f128;
    pub const fn algebraic_rem(self, rhs: f128) -> f128;
}

// core::intrinsics

pub const fn fadd_algebraic<T: Copy>(a: T, b: T) -> T;
pub const fn fsub_algebraic<T: Copy>(a: T, b: T) -> T;
pub const fn fmul_algebraic<T: Copy>(a: T, b: T) -> T;
pub const fn fdiv_algebraic<T: Copy>(a: T, b: T) -> T;
pub const fn frem_algebraic<T: Copy>(a: T, b: T) -> T;
```

This PR does not preserve the initial behaviour of these functions yielding non-deterministic output under Miri; it is most likely desired to reimplement this behaviour at some point.

5 files changed, 45 insertions, 25 deletions

diff --git a/library/core/src/intrinsics/mod.rs b/library/core/src/intrinsics/mod.rs
index 79f300c295b..a7563f918a2 100644
--- a/library/core/src/intrinsics/mod.rs
+++ b/library/core/src/intrinsics/mod.rs
@@ -2430,35 +2430,35 @@ pub unsafe fn float_to_int_unchecked<Float: Copy, Int: Copy>(value: Float) -> In
 /// Stabilized as [`f16::algebraic_add`], [`f32::algebraic_add`], [`f64::algebraic_add`] and [`f128::algebraic_add`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
-pub fn fadd_algebraic<T: Copy>(a: T, b: T) -> T;
+pub const fn fadd_algebraic<T: Copy>(a: T, b: T) -> T;
 
 /// Float subtraction that allows optimizations based on algebraic rules.
 ///
 /// Stabilized as [`f16::algebraic_sub`], [`f32::algebraic_sub`], [`f64::algebraic_sub`] and [`f128::algebraic_sub`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
-pub fn fsub_algebraic<T: Copy>(a: T, b: T) -> T;
+pub const fn fsub_algebraic<T: Copy>(a: T, b: T) -> T;
 
 /// Float multiplication that allows optimizations based on algebraic rules.
 ///
 /// Stabilized as [`f16::algebraic_mul`], [`f32::algebraic_mul`], [`f64::algebraic_mul`] and [`f128::algebraic_mul`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
-pub fn fmul_algebraic<T: Copy>(a: T, b: T) -> T;
+pub const fn fmul_algebraic<T: Copy>(a: T, b: T) -> T;
 
 /// Float division that allows optimizations based on algebraic rules.
 ///
 /// Stabilized as [`f16::algebraic_div`], [`f32::algebraic_div`], [`f64::algebraic_div`] and [`f128::algebraic_div`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
-pub fn fdiv_algebraic<T: Copy>(a: T, b: T) -> T;
+pub const fn fdiv_algebraic<T: Copy>(a: T, b: T) -> T;
 
 /// Float remainder that allows optimizations based on algebraic rules.
 ///
 /// Stabilized as [`f16::algebraic_rem`], [`f32::algebraic_rem`], [`f64::algebraic_rem`] and [`f128::algebraic_rem`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
-pub fn frem_algebraic<T: Copy>(a: T, b: T) -> T;
+pub const fn frem_algebraic<T: Copy>(a: T, b: T) -> T;
 
 /// Returns the number of bits set in an integer type `T`
 ///
diff --git a/library/core/src/num/f128.rs b/library/core/src/num/f128.rs
index 8a72779ce87..b1119d4899b 100644
--- a/library/core/src/num/f128.rs
+++ b/library/core/src/num/f128.rs
@@ -1382,8 +1382,9 @@ impl f128 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_add(self, rhs: f128) -> f128 {
+    pub const fn algebraic_add(self, rhs: f128) -> f128 {
         intrinsics::fadd_algebraic(self, rhs)
     }
 
@@ -1392,8 +1393,9 @@ impl f128 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_sub(self, rhs: f128) -> f128 {
+    pub const fn algebraic_sub(self, rhs: f128) -> f128 {
         intrinsics::fsub_algebraic(self, rhs)
     }
 
@@ -1402,8 +1404,9 @@ impl f128 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_mul(self, rhs: f128) -> f128 {
+    pub const fn algebraic_mul(self, rhs: f128) -> f128 {
         intrinsics::fmul_algebraic(self, rhs)
     }
 
@@ -1412,8 +1415,9 @@ impl f128 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_div(self, rhs: f128) -> f128 {
+    pub const fn algebraic_div(self, rhs: f128) -> f128 {
         intrinsics::fdiv_algebraic(self, rhs)
     }
 
@@ -1422,8 +1426,9 @@ impl f128 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_rem(self, rhs: f128) -> f128 {
+    pub const fn algebraic_rem(self, rhs: f128) -> f128 {
         intrinsics::frem_algebraic(self, rhs)
     }
 }
diff --git a/library/core/src/num/f16.rs b/library/core/src/num/f16.rs
index afed6f04059..54e38d9e1a6 100644
--- a/library/core/src/num/f16.rs
+++ b/library/core/src/num/f16.rs
@@ -1358,8 +1358,9 @@ impl f16 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_add(self, rhs: f16) -> f16 {
+    pub const fn algebraic_add(self, rhs: f16) -> f16 {
         intrinsics::fadd_algebraic(self, rhs)
     }
 
@@ -1368,8 +1369,9 @@ impl f16 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_sub(self, rhs: f16) -> f16 {
+    pub const fn algebraic_sub(self, rhs: f16) -> f16 {
         intrinsics::fsub_algebraic(self, rhs)
     }
 
@@ -1378,8 +1380,9 @@ impl f16 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_mul(self, rhs: f16) -> f16 {
+    pub const fn algebraic_mul(self, rhs: f16) -> f16 {
         intrinsics::fmul_algebraic(self, rhs)
     }
 
@@ -1388,8 +1391,9 @@ impl f16 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_div(self, rhs: f16) -> f16 {
+    pub const fn algebraic_div(self, rhs: f16) -> f16 {
         intrinsics::fdiv_algebraic(self, rhs)
     }
 
@@ -1398,8 +1402,9 @@ impl f16 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_rem(self, rhs: f16) -> f16 {
+    pub const fn algebraic_rem(self, rhs: f16) -> f16 {
         intrinsics::frem_algebraic(self, rhs)
     }
 }
diff --git a/library/core/src/num/f32.rs b/library/core/src/num/f32.rs
index 44d87f3c93a..e66fd3bb52b 100644
--- a/library/core/src/num/f32.rs
+++ b/library/core/src/num/f32.rs
@@ -1523,8 +1523,9 @@ impl f32 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_add(self, rhs: f32) -> f32 {
+    pub const fn algebraic_add(self, rhs: f32) -> f32 {
         intrinsics::fadd_algebraic(self, rhs)
     }
 
@@ -1533,8 +1534,9 @@ impl f32 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_sub(self, rhs: f32) -> f32 {
+    pub const fn algebraic_sub(self, rhs: f32) -> f32 {
         intrinsics::fsub_algebraic(self, rhs)
     }
 
@@ -1543,8 +1545,9 @@ impl f32 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_mul(self, rhs: f32) -> f32 {
+    pub const fn algebraic_mul(self, rhs: f32) -> f32 {
         intrinsics::fmul_algebraic(self, rhs)
     }
 
@@ -1553,8 +1556,9 @@ impl f32 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_div(self, rhs: f32) -> f32 {
+    pub const fn algebraic_div(self, rhs: f32) -> f32 {
         intrinsics::fdiv_algebraic(self, rhs)
     }
 
@@ -1563,8 +1567,9 @@ impl f32 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_rem(self, rhs: f32) -> f32 {
+    pub const fn algebraic_rem(self, rhs: f32) -> f32 {
         intrinsics::frem_algebraic(self, rhs)
     }
 }
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs
index e90af8774e4..2d791437b28 100644
--- a/library/core/src/num/f64.rs
+++ b/library/core/src/num/f64.rs
@@ -1522,8 +1522,9 @@ impl f64 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_add(self, rhs: f64) -> f64 {
+    pub const fn algebraic_add(self, rhs: f64) -> f64 {
         intrinsics::fadd_algebraic(self, rhs)
     }
 
@@ -1532,8 +1533,9 @@ impl f64 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_sub(self, rhs: f64) -> f64 {
+    pub const fn algebraic_sub(self, rhs: f64) -> f64 {
         intrinsics::fsub_algebraic(self, rhs)
     }
 
@@ -1542,8 +1544,9 @@ impl f64 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_mul(self, rhs: f64) -> f64 {
+    pub const fn algebraic_mul(self, rhs: f64) -> f64 {
         intrinsics::fmul_algebraic(self, rhs)
     }
 
@@ -1552,8 +1555,9 @@ impl f64 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_div(self, rhs: f64) -> f64 {
+    pub const fn algebraic_div(self, rhs: f64) -> f64 {
         intrinsics::fdiv_algebraic(self, rhs)
     }
 
@@ -1562,8 +1566,9 @@ impl f64 {
     /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[rustc_const_unstable(feature = "float_algebraic", issue = "136469")]
     #[inline]
-    pub fn algebraic_rem(self, rhs: f64) -> f64 {
+    pub const fn algebraic_rem(self, rhs: f64) -> f64 {
         intrinsics::frem_algebraic(self, rhs)
     }
 }