Optimize `ToString` implementation for integers

1 files changed, 48 insertions, 0 deletions

diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index 9a161d057db..1a0b3b43eb6 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -2824,7 +2824,54 @@ impl SpecToString for bool {
     }
 }
 
+macro_rules! impl_to_string {
+    ($($signed:ident, $unsigned:ident,)*) => {
+        $(
+        #[cfg(not(no_global_oom_handling))]
+        #[cfg(not(feature = "optimize_for_size"))]
+        impl SpecToString for $signed {
+            #[inline]
+            fn spec_to_string(&self) -> String {
+                const SIZE: usize = $signed::MAX.ilog(10) as usize + 1;
+                let mut buf = [core::mem::MaybeUninit::<u8>::uninit(); SIZE];
+                // Only difference between signed and unsigned are these 8 lines.
+                let mut out;
+                if *self < 0 {
+                    out = String::with_capacity(SIZE + 1);
+                    out.push('-');
+                } else {
+                    out = String::with_capacity(SIZE);
+                }
+
+                out.push_str(self.unsigned_abs()._fmt(&mut buf));
+                out
+            }
+        }
+        #[cfg(not(no_global_oom_handling))]
+        #[cfg(not(feature = "optimize_for_size"))]
+        impl SpecToString for $unsigned {
+            #[inline]
+            fn spec_to_string(&self) -> String {
+                const SIZE: usize = $unsigned::MAX.ilog(10) as usize + 1;
+                let mut buf = [core::mem::MaybeUninit::<u8>::uninit(); SIZE];
+
+                self._fmt(&mut buf).to_string()
+            }
+        }
+        )*
+    }
+}
+
+impl_to_string! {
+    i8, u8,
+    i16, u16,
+    i32, u32,
+    i64, u64,
+    isize, usize,
+}
+
 #[cfg(not(no_global_oom_handling))]
+#[cfg(feature = "optimize_for_size")]
 impl SpecToString for u8 {
     #[inline]
     fn spec_to_string(&self) -> String {
@@ -2844,6 +2891,7 @@ impl SpecToString for u8 {
 }
 
 #[cfg(not(no_global_oom_handling))]
+#[cfg(feature = "optimize_for_size")]
 impl SpecToString for i8 {
     #[inline]
     fn spec_to_string(&self) -> String {