1 files changed, 92 insertions, 0 deletions
diff --git a/src/char.rs b/src/char.rs
new file mode 100644
index 0000000..939b6b4
--- /dev/null
+++ b/src/char.rs
@@ -0,0 +1,92 @@
+// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//
+// Original authors: alexchrichton, bluss
+
+// UTF-8 ranges and tags for encoding characters
+const TAG_CONT: u8    = 0b1000_0000;
+const TAG_TWO_B: u8   = 0b1100_0000;
+const TAG_THREE_B: u8 = 0b1110_0000;
+const TAG_FOUR_B: u8  = 0b1111_0000;
+const MAX_ONE_B: u32   =     0x80;
+const MAX_TWO_B: u32   =    0x800;
+const MAX_THREE_B: u32 =  0x10000;
+
+/// Placeholder
+pub struct EncodeUtf8Error;
+
+/// Encode a char into buf using UTF-8.
+///
+/// On success, return the byte length of the encoding (1, 2, 3 or 4).<br>
+/// On error, return `EncodeUtf8Error` if the buffer was too short for the char.
+///
+/// Safety: `ptr` must be writable for `len` bytes.
+#[inline]
+pub unsafe fn encode_utf8(ch: char, ptr: *mut u8, len: usize) -> Result<usize, EncodeUtf8Error>
+{
+    let code = ch as u32;
+    if code < MAX_ONE_B && len >= 1 {
+        ptr.add(0).write(code as u8);
+        return Ok(1);
+    } else if code < MAX_TWO_B && len >= 2 {
+        ptr.add(0).write((code >> 6 & 0x1F) as u8 | TAG_TWO_B);
+        ptr.add(1).write((code & 0x3F) as u8 | TAG_CONT);
+        return Ok(2);
+    } else if code < MAX_THREE_B && len >= 3 {
+        ptr.add(0).write((code >> 12 & 0x0F) as u8 | TAG_THREE_B);
+        ptr.add(1).write((code >>  6 & 0x3F) as u8 | TAG_CONT);
+        ptr.add(2).write((code & 0x3F) as u8 | TAG_CONT);
+        return Ok(3);
+    } else if len >= 4 {
+        ptr.add(0).write((code >> 18 & 0x07) as u8 | TAG_FOUR_B);
+        ptr.add(1).write((code >> 12 & 0x3F) as u8 | TAG_CONT);
+        ptr.add(2).write((code >>  6 & 0x3F) as u8 | TAG_CONT);
+        ptr.add(3).write((code & 0x3F) as u8 | TAG_CONT);
+        return Ok(4);
+    };
+    Err(EncodeUtf8Error)
+}
+
+
+#[test]
+#[cfg_attr(miri, ignore)] // Miri is too slow
+fn test_encode_utf8() {
+    // Test that all codepoints are encoded correctly
+    let mut data = [0u8; 16];
+    for codepoint in 0..=(std::char::MAX as u32) {
+        if let Some(ch) = std::char::from_u32(codepoint) {
+            for elt in &mut data { *elt = 0; }
+            let ptr = data.as_mut_ptr();
+            let len = data.len();
+            unsafe {
+                let res = encode_utf8(ch, ptr, len).ok().unwrap();
+                assert_eq!(res, ch.len_utf8());
+            }
+            let string = std::str::from_utf8(&data).unwrap();
+            assert_eq!(string.chars().next(), Some(ch));
+        }
+    }
+}
+
+#[test]
+fn test_encode_utf8_oob() {
+    // test that we report oob if the buffer is too short
+    let mut data = [0u8; 16];
+    let chars = ['a', 'α', '�', '𐍈'];
+    for (len, &ch) in (1..=4).zip(&chars) {
+        assert_eq!(len, ch.len_utf8(), "Len of ch={}", ch);
+        let ptr = data.as_mut_ptr();
+        unsafe {
+            assert!(matches::matches!(encode_utf8(ch, ptr, len - 1), Err(_)));
+            assert!(matches::matches!(encode_utf8(ch, ptr, len), Ok(_)));
+        }
+    }
+}
+