From 763efbb3041d108ca0813485f3ec30bca5d61a2c Mon Sep 17 00:00:00 2001
From: "Shane F. Carr" <shane@unicode.org>
Date: Wed, 18 Aug 2021 03:01:09 -0500
Subject: [PATCH] Add Writeable impls for u8 and u16 for another small code
 size improvement

---
 provider/core/src/resource.rs | 23 +++------
 utils/writeable/src/impls.rs  | 91 +++++++++++++++++++++++++++++++++++
 utils/writeable/src/lib.rs    |  1 +
 3 files changed, 99 insertions(+), 16 deletions(-)
 create mode 100644 utils/writeable/src/impls.rs

diff --git a/provider/core/src/resource.rs b/provider/core/src/resource.rs
index b3a357de323..a425bc8fb09 100644
--- a/provider/core/src/resource.rs
+++ b/provider/core/src/resource.rs
@@ -16,6 +16,7 @@ use core::fmt;
 use core::fmt::Write;
 use icu_locid::LanguageIdentifier;
 use tinystr::{TinyStr16, TinyStr4};
+use writeable::{LengthHint, Writeable};
 
 /// A top-level collection of related resource keys.
 #[non_exhaustive]
@@ -133,35 +134,25 @@ impl fmt::Debug for ResourceKey {
 
 impl fmt::Display for ResourceKey {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        writeable::Writeable::write_to(self, f)
+        Writeable::write_to(self, f)
     }
 }
 
-impl writeable::Writeable for ResourceKey {
+impl Writeable for ResourceKey {
     fn write_to<W: core::fmt::Write + ?Sized>(&self, sink: &mut W) -> core::fmt::Result {
         sink.write_str(&self.category.as_str())?;
         sink.write_char('/')?;
         sink.write_str(self.sub_category.as_str())?;
         sink.write_char('@')?;
-        write!(sink, "{}", self.version)?;
+        self.version.write_to(sink)?;
         Ok(())
     }
 
-    fn write_len(&self) -> writeable::LengthHint {
-        writeable::LengthHint::Exact(2)
+    fn write_len(&self) -> LengthHint {
+        LengthHint::Exact(2)
             + self.category.as_str().len()
             + self.sub_category.len()
-            + if self.version < 10 {
-                1
-            } else if self.version < 100 {
-                2
-            } else if self.version < 1000 {
-                3
-            } else if self.version < 10000 {
-                4
-            } else {
-                5
-            }
+            + self.version.write_len()
     }
 }
 
diff --git a/utils/writeable/src/impls.rs b/utils/writeable/src/impls.rs
new file mode 100644
index 00000000000..4d4f6d2244f
--- /dev/null
+++ b/utils/writeable/src/impls.rs
@@ -0,0 +1,91 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+use crate::LengthHint;
+use crate::Writeable;
+use core::convert::TryFrom;
+use core::fmt;
+use core::str;
+
+impl Writeable for u8 {
+    fn write_to<W: fmt::Write + ?Sized>(&self, sink: &mut W) -> fmt::Result {
+        let mut buf = [b'0'; 3];
+        let mut n = *self;
+        let mut i = 3usize;
+        while n != 0 {
+            i -= 1;
+            buf[i] = b'0' + (n % 10);
+            n /= 10;
+        }
+        if i == 3 {
+            debug_assert_eq!(*self, 0);
+            i = 2;
+        }
+        let s = unsafe { str::from_utf8_unchecked(&buf[i..]) };
+        sink.write_str(s)
+    }
+
+    fn write_len(&self) -> LengthHint {
+        if *self < 10 {
+            LengthHint::Exact(1)
+        } else if *self < 100 {
+            LengthHint::Exact(2)
+        } else {
+            LengthHint::Exact(3)
+        }
+    }
+}
+
+impl Writeable for u16 {
+    fn write_to<W: fmt::Write + ?Sized>(&self, sink: &mut W) -> fmt::Result {
+        let mut buf = [b'0'; 5];
+        let mut n = *self;
+        let mut i = 5usize;
+        while n != 0 {
+            i -= 1;
+            buf[i] = b'0' + u8::try_from(n % 10).expect("<10");
+            n /= 10;
+        }
+        if i == 5 {
+            debug_assert_eq!(*self, 0);
+            i = 4;
+        }
+        let s = unsafe { str::from_utf8_unchecked(&buf[i..]) };
+        sink.write_str(s)
+    }
+
+    fn write_len(&self) -> LengthHint {
+        if *self < 10 {
+            LengthHint::Exact(1)
+        } else if *self < 100 {
+            LengthHint::Exact(2)
+        } else if *self < 1000 {
+            LengthHint::Exact(3)
+        } else if *self < 10000 {
+            LengthHint::Exact(4)
+        } else {
+            LengthHint::Exact(5)
+        }
+    }
+}
+
+#[test]
+fn test_u8() {
+    use crate::assert_writeable_eq;
+    assert_writeable_eq!("0", &0u8);
+    assert_writeable_eq!("1", &1u8);
+    assert_writeable_eq!("10", &10u8);
+    assert_writeable_eq!("99", &99u8);
+    assert_writeable_eq!("255", &255u8);
+}
+
+#[test]
+fn test_u16() {
+    use crate::assert_writeable_eq;
+    assert_writeable_eq!("0", &0u16);
+    assert_writeable_eq!("1", &1u16);
+    assert_writeable_eq!("10", &10u16);
+    assert_writeable_eq!("99", &99u16);
+    assert_writeable_eq!("65535", &65535u16);
+}
diff --git a/utils/writeable/src/lib.rs b/utils/writeable/src/lib.rs
index 3bf9712804c..7b8cb88f517 100644
--- a/utils/writeable/src/lib.rs
+++ b/utils/writeable/src/lib.rs
@@ -53,6 +53,7 @@
 
 extern crate alloc;
 
+mod impls;
 mod ops;
 
 use alloc::string::String;