Rollup merge of rust-lang#87500 - Smittyvb:min-max-docs, r=kennytm

Document math behind MIN/MAX consts on integers Currently the documentation for `[integer]::{MIN, MAX}` doesn't explain where the constants come from. This documents how the values of those constants are related to powers of 2.
JohnTitor · Jul 28, 2021 · ca62d19 · ca62d19
2 parents e5677a6 + 0e01749
commit ca62d19
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Showing 3 changed files with 15 additions and 12 deletions.
diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
@@ -1,9 +1,10 @@
 macro_rules! int_impl {
-    ($SelfT:ty, $ActualT:ident, $UnsignedT:ty, $BITS:expr, $Min:expr, $Max:expr,
+    ($SelfT:ty, $ActualT:ident, $UnsignedT:ty, $BITS:expr, $BITS_MINUS_ONE:expr, $Min:expr, $Max:expr,
      $rot:expr, $rot_op:expr, $rot_result:expr, $swap_op:expr, $swapped:expr,
      $reversed:expr, $le_bytes:expr, $be_bytes:expr,
      $to_xe_bytes_doc:expr, $from_xe_bytes_doc:expr) => {
-        /// The smallest value that can be represented by this integer type.
+        /// The smallest value that can be represented by this integer type,
+        #[doc = concat!("-2<sup>", $BITS_MINUS_ONE, "</sup>.")]
         ///
         /// # Examples
         ///
@@ -15,7 +16,8 @@ macro_rules! int_impl {
         #[stable(feature = "assoc_int_consts", since = "1.43.0")]
         pub const MIN: Self = !0 ^ ((!0 as $UnsignedT) >> 1) as Self;
 
-        /// The largest value that can be represented by this integer type.
+        /// The largest value that can be represented by this integer type,
+        #[doc = concat!("2<sup>", $BITS_MINUS_ONE, "</sup> - 1.")]
         ///
         /// # Examples
         ///

diff --git a/library/core/src/num/mod.rs b/library/core/src/num/mod.rs
@@ -91,34 +91,34 @@ depending on the target pointer size.
 
 #[lang = "i8"]
 impl i8 {
-    int_impl! { i8, i8, u8, 8, -128, 127, 2, "-0x7e", "0xa", "0x12", "0x12", "0x48",
+    int_impl! { i8, i8, u8, 8, 7, -128, 127, 2, "-0x7e", "0xa", "0x12", "0x12", "0x48",
     "[0x12]", "[0x12]", "", "" }
 }
 
 #[lang = "i16"]
 impl i16 {
-    int_impl! { i16, i16, u16, 16, -32768, 32767, 4, "-0x5ffd", "0x3a", "0x1234", "0x3412",
+    int_impl! { i16, i16, u16, 16, 15, -32768, 32767, 4, "-0x5ffd", "0x3a", "0x1234", "0x3412",
     "0x2c48", "[0x34, 0x12]", "[0x12, 0x34]", "", "" }
 }
 
 #[lang = "i32"]
 impl i32 {
-    int_impl! { i32, i32, u32, 32, -2147483648, 2147483647, 8, "0x10000b3", "0xb301",
+    int_impl! { i32, i32, u32, 32, 31, -2147483648, 2147483647, 8, "0x10000b3", "0xb301",
     "0x12345678", "0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]",
     "[0x12, 0x34, 0x56, 0x78]", "", "" }
 }
 
 #[lang = "i64"]
 impl i64 {
-    int_impl! { i64, i64, u64, 64, -9223372036854775808, 9223372036854775807, 12,
+    int_impl! { i64, i64, u64, 64, 63, -9223372036854775808, 9223372036854775807, 12,
     "0xaa00000000006e1", "0x6e10aa", "0x1234567890123456", "0x5634129078563412",
     "0x6a2c48091e6a2c48", "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
     "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]", "", "" }
 }
 
 #[lang = "i128"]
 impl i128 {
-    int_impl! { i128, i128, u128, 128, -170141183460469231731687303715884105728,
+    int_impl! { i128, i128, u128, 128, 127, -170141183460469231731687303715884105728,
     170141183460469231731687303715884105727, 16,
     "0x13f40000000000000000000000004f76", "0x4f7613f4", "0x12345678901234567890123456789012",
     "0x12907856341290785634129078563412", "0x48091e6a2c48091e6a2c48091e6a2c48",
@@ -131,15 +131,15 @@ impl i128 {
 #[cfg(target_pointer_width = "16")]
 #[lang = "isize"]
 impl isize {
-    int_impl! { isize, i16, usize, 16, -32768, 32767, 4, "-0x5ffd", "0x3a", "0x1234",
+    int_impl! { isize, i16, usize, 16, 15, -32768, 32767, 4, "-0x5ffd", "0x3a", "0x1234",
     "0x3412", "0x2c48", "[0x34, 0x12]", "[0x12, 0x34]",
     usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!() }
 }
 
 #[cfg(target_pointer_width = "32")]
 #[lang = "isize"]
 impl isize {
-    int_impl! { isize, i32, usize, 32, -2147483648, 2147483647, 8, "0x10000b3", "0xb301",
+    int_impl! { isize, i32, usize, 32, 31, -2147483648, 2147483647, 8, "0x10000b3", "0xb301",
     "0x12345678", "0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]",
     "[0x12, 0x34, 0x56, 0x78]",
     usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!() }
@@ -148,7 +148,7 @@ impl isize {
 #[cfg(target_pointer_width = "64")]
 #[lang = "isize"]
 impl isize {
-    int_impl! { isize, i64, usize, 64, -9223372036854775808, 9223372036854775807,
+    int_impl! { isize, i64, usize, 64, 63, -9223372036854775808, 9223372036854775807,
     12, "0xaa00000000006e1", "0x6e10aa",  "0x1234567890123456", "0x5634129078563412",
      "0x6a2c48091e6a2c48", "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
      "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",

diff --git a/library/core/src/num/uint_macros.rs b/library/core/src/num/uint_macros.rs
@@ -15,7 +15,8 @@ macro_rules! uint_impl {
         #[stable(feature = "assoc_int_consts", since = "1.43.0")]
         pub const MIN: Self = 0;
 
-        /// The largest value that can be represented by this integer type.
+        /// The largest value that can be represented by this integer type,
+        #[doc = concat!("2<sup>", $BITS, "</sup> - 1.")]
         ///
         /// # Examples
         ///