Auto merge of #65107 - llogiq:const-checked, r=<try>

constify some checked arithmetics

This makes the `checked_`{`add`, `sub`, `mul`, "neg", "shl", "shr"} operations const fns. Division is a bit more involved. I guess I could solve it with some trickery, but I'm not sure if it would negatively affect performance, so I stopped there.

Author: bors

src/libcore/num/mod.rs

@@ -626,9 +626,9 @@ $EndFeature, "
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_add(self, rhs: Self) -> Option<Self> {
+            pub const fn checked_add(self, rhs: Self) -> Option<Self> {
                 let (a, b) = self.overflowing_add(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -650,9 +650,9 @@ $EndFeature, "
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_sub(self, rhs: Self) -> Option<Self> {
+            pub const fn checked_sub(self, rhs: Self) -> Option<Self> {
                 let (a, b) = self.overflowing_sub(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -674,9 +674,9 @@ $EndFeature, "
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_mul(self, rhs: Self) -> Option<Self> {
+            pub const fn checked_mul(self, rhs: Self) -> Option<Self> {
                 let (a, b) = self.overflowing_mul(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -808,9 +808,9 @@ $EndFeature, "
 ```"),
             #[stable(feature = "wrapping", since = "1.7.0")]
             #[inline]
-            pub fn checked_neg(self) -> Option<Self> {
+            pub const fn checked_neg(self) -> Option<Self> {
                 let (a, b) = self.overflowing_neg();
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -831,9 +831,9 @@ $EndFeature, "
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_shl(self, rhs: u32) -> Option<Self> {
+            pub const fn checked_shl(self, rhs: u32) -> Option<Self> {
                 let (a, b) = self.overflowing_shl(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -854,9 +854,9 @@ $EndFeature, "
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_shr(self, rhs: u32) -> Option<Self> {
+            pub const fn checked_shr(self, rhs: u32) -> Option<Self> {
                 let (a, b) = self.overflowing_shr(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -2679,9 +2679,9 @@ assert_eq!((", stringify!($SelfT), "::max_value() - 2).checked_add(3), None);",
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_add(self, rhs: Self) -> Option<Self> {
+            pub const fn checked_add(self, rhs: Self) -> Option<Self> {
                 let (a, b) = self.overflowing_add(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -2701,9 +2701,9 @@ assert_eq!(0", stringify!($SelfT), ".checked_sub(1), None);", $EndFeature, "
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_sub(self, rhs: Self) -> Option<Self> {
+            pub const fn checked_sub(self, rhs: Self) -> Option<Self> {
                 let (a, b) = self.overflowing_sub(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -2723,9 +2723,9 @@ assert_eq!(", stringify!($SelfT), "::max_value().checked_mul(2), None);", $EndFe
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_mul(self, rhs: Self) -> Option<Self> {
+            pub const fn checked_mul(self, rhs: Self) -> Option<Self> {
                 let (a, b) = self.overflowing_mul(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -2845,9 +2845,9 @@ assert_eq!(1", stringify!($SelfT), ".checked_neg(), None);", $EndFeature, "
 ```"),
             #[stable(feature = "wrapping", since = "1.7.0")]
             #[inline]
-            pub fn checked_neg(self) -> Option<Self> {
+            pub const fn checked_neg(self) -> Option<Self> {
                 let (a, b) = self.overflowing_neg();
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -2867,9 +2867,9 @@ assert_eq!(0x10", stringify!($SelfT), ".checked_shl(129), None);", $EndFeature,
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_shl(self, rhs: u32) -> Option<Self> {
+            pub const fn checked_shl(self, rhs: u32) -> Option<Self> {
                 let (a, b) = self.overflowing_shl(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }
 
@@ -2889,9 +2889,9 @@ assert_eq!(0x10", stringify!($SelfT), ".checked_shr(129), None);", $EndFeature,
             #[must_use = "this returns the result of the operation, \
                           without modifying the original"]
             #[inline]
-            pub fn checked_shr(self, rhs: u32) -> Option<Self> {
+            pub const fn checked_shr(self, rhs: u32) -> Option<Self> {
                 let (a, b) = self.overflowing_shr(rhs);
-                if b {None} else {Some(a)}
+                [Some(a), None][b as usize]
             }
         }