Auto merge of #43248 - llogiq:num-try-from, r=nagisa

improve the TryFrom implementations

This removes the need for a 128 bit storage by making use of the fact that there can be either no over/underflow, either one or both, and each time the target type suffices to hold the limit for comparison. This also means that the implementation will work in targets without 128bit support (unless it's for 128bit types, of course).

The downside is that the code looks a bit more complex.

Author: bors

src/libcore/num/mod.rs

@@ -2504,76 +2504,209 @@ impl fmt::Display for TryFromIntError {
     }
 }
 
-macro_rules! same_sign_try_from_int_impl {
-    ($storage:ty, $target:ty, $($source:ty),*) => {$(
+// no possible bounds violation
+macro_rules! try_from_unbounded {
+    ($source:ty, $($target:ty),*) => {$(
         #[unstable(feature = "try_from", issue = "33417")]
         impl TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
+            #[inline]
             fn try_from(u: $source) -> Result<$target, TryFromIntError> {
-                let min = <$target as FromStrRadixHelper>::min_value() as $storage;
-                let max = <$target as FromStrRadixHelper>::max_value() as $storage;
-                if u as $storage < min || u as $storage > max {
-                    Err(TryFromIntError(()))
-                } else {
+                Ok(u as $target)
+            }
+        }
+    )*}
+}
+
+// only negative bounds
+macro_rules! try_from_lower_bounded {
+    ($source:ty, $($target:ty),*) => {$(
+        #[unstable(feature = "try_from", issue = "33417")]
+        impl TryFrom<$source> for $target {
+            type Error = TryFromIntError;
+
+            #[inline]
+            fn try_from(u: $source) -> Result<$target, TryFromIntError> {
+                if u >= 0 {
                     Ok(u as $target)
+                } else {
+                    Err(TryFromIntError(()))
                 }
             }
         }
     )*}
 }
 
-same_sign_try_from_int_impl!(u128, u8, u8, u16, u32, u64, u128, usize);
-same_sign_try_from_int_impl!(i128, i8, i8, i16, i32, i64, i128, isize);
-same_sign_try_from_int_impl!(u128, u16, u8, u16, u32, u64, u128, usize);
-same_sign_try_from_int_impl!(i128, i16, i8, i16, i32, i64, i128, isize);
-same_sign_try_from_int_impl!(u128, u32, u8, u16, u32, u64, u128, usize);
-same_sign_try_from_int_impl!(i128, i32, i8, i16, i32, i64, i128, isize);
-same_sign_try_from_int_impl!(u128, u64, u8, u16, u32, u64, u128, usize);
-same_sign_try_from_int_impl!(i128, i64, i8, i16, i32, i64, i128, isize);
-same_sign_try_from_int_impl!(u128, u128, u8, u16, u32, u64, u128, usize);
-same_sign_try_from_int_impl!(i128, i128, i8, i16, i32, i64, i128, isize);
-same_sign_try_from_int_impl!(u128, usize, u8, u16, u32, u64, u128, usize);
-same_sign_try_from_int_impl!(i128, isize, i8, i16, i32, i64, i128, isize);
-
-macro_rules! cross_sign_from_int_impl {
-    ($unsigned:ty, $($signed:ty),*) => {$(
+// unsigned to signed (only positive bound)
+macro_rules! try_from_upper_bounded {
+    ($source:ty, $($target:ty),*) => {$(
         #[unstable(feature = "try_from", issue = "33417")]
-        impl TryFrom<$unsigned> for $signed {
+        impl TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
-            fn try_from(u: $unsigned) -> Result<$signed, TryFromIntError> {
-                let max = <$signed as FromStrRadixHelper>::max_value() as u128;
-                if u as u128 > max {
+            #[inline]
+            fn try_from(u: $source) -> Result<$target, TryFromIntError> {
+                if u > (<$target>::max_value() as $source) {
                     Err(TryFromIntError(()))
                 } else {
-                    Ok(u as $signed)
+                    Ok(u as $target)
                 }
             }
         }
+    )*}
+}
 
+// all other cases
+macro_rules! try_from_both_bounded {
+    ($source:ty, $($target:ty),*) => {$(
         #[unstable(feature = "try_from", issue = "33417")]
-        impl TryFrom<$signed> for $unsigned {
+        impl TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
-            fn try_from(u: $signed) -> Result<$unsigned, TryFromIntError> {
-                let max = <$unsigned as FromStrRadixHelper>::max_value() as u128;
-                if u < 0 || u as u128 > max {
+            #[inline]
+            fn try_from(u: $source) -> Result<$target, TryFromIntError> {
+                let min = <$target>::min_value() as $source;
+                let max = <$target>::max_value() as $source;
+                if u < min || u > max {
                     Err(TryFromIntError(()))
                 } else {
-                    Ok(u as $unsigned)
+                    Ok(u as $target)
                 }
             }
         }
     )*}
 }
 
-cross_sign_from_int_impl!(u8, i8, i16, i32, i64, i128, isize);
-cross_sign_from_int_impl!(u16, i8, i16, i32, i64, i128, isize);
-cross_sign_from_int_impl!(u32, i8, i16, i32, i64, i128, isize);
-cross_sign_from_int_impl!(u64, i8, i16, i32, i64, i128, isize);
-cross_sign_from_int_impl!(u128, i8, i16, i32, i64, i128, isize);
-cross_sign_from_int_impl!(usize, i8, i16, i32, i64, i128, isize);
+macro_rules! rev {
+    ($mac:ident, $source:ty, $($target:ty),*) => {$(
+        $mac!($target, $source);
+    )*}
+}
+
+/// intra-sign conversions
+try_from_unbounded!(u8, u8, u16, u32, u64, u128);
+try_from_unbounded!(u16, u16, u32, u64, u128);
+try_from_unbounded!(u32, u32, u64, u128);
+try_from_unbounded!(u64, u64, u128);
+try_from_unbounded!(u128, u128);
+try_from_upper_bounded!(u16, u8);
+try_from_upper_bounded!(u32, u16, u8);
+try_from_upper_bounded!(u64, u32, u16, u8);
+try_from_upper_bounded!(u128, u64, u32, u16, u8);
+
+try_from_unbounded!(i8, i8, i16, i32, i64, i128);
+try_from_unbounded!(i16, i16, i32, i64, i128);
+try_from_unbounded!(i32, i32, i64, i128);
+try_from_unbounded!(i64, i64, i128);
+try_from_unbounded!(i128, i128);
+try_from_both_bounded!(i16, i8);
+try_from_both_bounded!(i32, i16, i8);
+try_from_both_bounded!(i64, i32, i16, i8);
+try_from_both_bounded!(i128, i64, i32, i16, i8);
+
+// unsigned-to-signed
+try_from_unbounded!(u8, i16, i32, i64, i128);
+try_from_unbounded!(u16, i32, i64, i128);
+try_from_unbounded!(u32, i64, i128);
+try_from_unbounded!(u64, i128);
+try_from_upper_bounded!(u8, i8);
+try_from_upper_bounded!(u16, i8, i16);
+try_from_upper_bounded!(u32, i8, i16, i32);
+try_from_upper_bounded!(u64, i8, i16, i32, i64);
+try_from_upper_bounded!(u128, i8, i16, i32, i64, i128);
+
+// signed-to-unsigned
+try_from_lower_bounded!(i8, u8, u16, u32, u64, u128);
+try_from_lower_bounded!(i16, u16, u32, u64, u128);
+try_from_lower_bounded!(i32, u32, u64, u128);
+try_from_lower_bounded!(i64, u64, u128);
+try_from_lower_bounded!(i128, u128);
+try_from_both_bounded!(i16, u8);
+try_from_both_bounded!(i32, u16, u8);
+try_from_both_bounded!(i64, u32, u16, u8);
+try_from_both_bounded!(i128, u64, u32, u16, u8);
+
+#[unstable(feature = "try_from", issue = "33417")]
+pub use self::ptr_try_from_impls::*;
+
+#[cfg(target_pointer_width = "16")]
+mod ptr_try_from_impls {
+    use super::TryFromIntError;
+    use convert::TryFrom;
+
+    try_from_upper_bounded!(usize, u8);
+    try_from_unbounded!(usize, usize, u16, u32, u64, u128);
+    try_from_upper_bounded!(usize, i8, i16, isize);
+    try_from_unbounded!(usize, i32, i64, i128);
+
+    try_from_both_bounded!(isize, u8);
+    try_from_lower_bounded!(isize, usize, u16, u32, u64, u128);
+    try_from_both_bounded!(isize, i8);
+    try_from_unbounded!(isize, i16, i32, i64, i128);
+
+    rev!(try_from_unbounded, usize, u8, u16);
+    rev!(try_from_upper_bounded, usize, u32, u64, u128);
+    rev!(try_from_lower_bounded, usize, i8, i16);
+    rev!(try_from_both_bounded, usize, i32, i64, i128);
+
+    rev!(try_from_unbounded, isize, u8);
+    rev!(try_from_upper_bounded, isize, u16, u32, u64, u128);
+    rev!(try_from_unbounded, isize, i8, i16);
+    rev!(try_from_both_bounded, isize, i32, i64, i128);
+}
+
+#[cfg(target_pointer_width = "32")]
+mod ptr_try_from_impls {
+    use super::TryFromIntError;
+    use convert::TryFrom;
+
+    try_from_upper_bounded!(usize, u8, u16);
+    try_from_unbounded!(usize, usize, u32, u64, u128);
+    try_from_upper_bounded!(usize, i8, i16, i32, isize);
+    try_from_unbounded!(usize, i64, i128);
+
+    try_from_both_bounded!(isize, u8, u16);
+    try_from_lower_bounded!(isize, usize, u32, u64, u128);
+    try_from_both_bounded!(isize, i8, i16);
+    try_from_unbounded!(isize, i32, i64, i128);
+
+    rev!(try_from_unbounded, usize, u8, u16, u32);
+    rev!(try_from_upper_bounded, usize, u64, u128);
+    rev!(try_from_lower_bounded, usize, i8, i16, i32);
+    rev!(try_from_both_bounded, usize, i64, i128);
+
+    rev!(try_from_unbounded, isize, u8, u16);
+    rev!(try_from_upper_bounded, isize, u32, u64, u128);
+    rev!(try_from_unbounded, isize, i8, i16, i32);
+    rev!(try_from_both_bounded, isize, i64, i128);
+}
+
+#[cfg(target_pointer_width = "64")]
+mod ptr_try_from_impls {
+    use super::TryFromIntError;
+    use convert::TryFrom;
+
+    try_from_upper_bounded!(usize, u8, u16, u32);
+    try_from_unbounded!(usize, usize, u64, u128);
+    try_from_upper_bounded!(usize, i8, i16, i32, i64, isize);
+    try_from_unbounded!(usize, i128);
+
+    try_from_both_bounded!(isize, u8, u16, u32);
+    try_from_lower_bounded!(isize, usize, u64, u128);
+    try_from_both_bounded!(isize, i8, i16, i32);
+    try_from_unbounded!(isize, i64, i128);
+
+    rev!(try_from_unbounded, usize, u8, u16, u32, u64);
+    rev!(try_from_upper_bounded, usize, u128);
+    rev!(try_from_lower_bounded, usize, i8, i16, i32, i64);
+    rev!(try_from_both_bounded, usize, i128);
+
+    rev!(try_from_unbounded, isize, u8, u16, u32);
+    rev!(try_from_upper_bounded, isize, u64, u128);
+    rev!(try_from_unbounded, isize, i8, i16, i32, i64);
+    rev!(try_from_both_bounded, isize, i128);
+}
 
 #[doc(hidden)]
 trait FromStrRadixHelper: PartialOrd + Copy {
@@ -2587,15 +2720,21 @@ trait FromStrRadixHelper: PartialOrd + Copy {
 
 macro_rules! doit {
     ($($t:ty)*) => ($(impl FromStrRadixHelper for $t {
+        #[inline]
         fn min_value() -> Self { Self::min_value() }
+        #[inline]
         fn max_value() -> Self { Self::max_value() }
+        #[inline]
         fn from_u32(u: u32) -> Self { u as Self }
+        #[inline]
         fn checked_mul(&self, other: u32) -> Option<Self> {
             Self::checked_mul(*self, other as Self)
         }
+        #[inline]
         fn checked_sub(&self, other: u32) -> Option<Self> {
             Self::checked_sub(*self, other as Self)
         }
+        #[inline]
         fn checked_add(&self, other: u32) -> Option<Self> {
             Self::checked_add(*self, other as Self)
         }