Port multibyte-char-to-unibyte

rust_src/src/character.rs

@@ -1,7 +1,7 @@
 //! Operations on characters.
 
 use lisp::LispObject;
-use multibyte::{MAX_CHAR, make_char_multibyte};
+use multibyte::{MAX_CHAR, make_char_multibyte, raw_byte_from_codepoint_safe};
 use remacs_macros::lisp_fn;
 use remacs_sys::{EmacsInt, error};
 
@@ -38,3 +38,17 @@ fn unibyte_char_to_multibyte(ch: LispObject) -> LispObject {
     }
     LispObject::from_fixnum(make_char_multibyte(c) as EmacsInt)
 }
+
+/// Convert the multibyte character CH to a byte.
+/// If the multibyte character does not represent a byte, return -1.
+#[lisp_fn]
+fn multibyte_char_to_unibyte(ch: LispObject) -> LispObject {
+    let c = ch.as_character_or_error();
+    if c < 256 {
+        // Can't distinguish a byte read from a unibyte buffer from
+        // a latin1 char, so let's let it slide.
+        ch
+    } else {
+        LispObject::from_fixnum(raw_byte_from_codepoint_safe(c))
+    }
+}

rust_src/src/lib.rs

@@ -202,6 +202,7 @@ pub extern "C" fn rust_init_syms() {
         defsubr(&*character::Scharacterp);
         defsubr(&*character::Schar_or_string_p);
         defsubr(&*character::Sunibyte_char_to_multibyte);
+        defsubr(&*character::Smultibyte_char_to_unibyte);
         defsubr(&*vectors::Sarrayp);
         defsubr(&*vectors::Sbool_vector_p);
         defsubr(&*vectors::Sbufferp);

rust_src/src/multibyte.rs

@@ -191,6 +191,20 @@ fn raw_byte_from_codepoint(cp: Codepoint) -> c_uchar {
     (cp - 0x3F_FF00) as c_uchar
 }
 
+/// Same as the CHAR_TO_BYTE_SAFE macro.
+/// Return the raw 8-bit byte for character CP,
+/// or -1 if CP doesn't correspond to a byte.
+#[inline]
+pub fn raw_byte_from_codepoint_safe(cp: Codepoint) -> EmacsInt {
+    if cp < 0x80 {
+        cp as EmacsInt
+    } else if cp > MAX_5_BYTE_CHAR {
+        raw_byte_from_codepoint(cp) as EmacsInt
+    } else {
+        -1
+    }
+}
+
 /// UNIBYTE_TO_CHAR macro
 #[inline]
 pub fn unibyte_to_char(cp: Codepoint) -> Codepoint {

src/character.c

@@ -67,28 +67,6 @@ translate_char (Lisp_Object table, int c)
   return c;
 }
 
-DEFUN ("multibyte-char-to-unibyte", Fmultibyte_char_to_unibyte,
-       Smultibyte_char_to_unibyte, 1, 1, 0,
-       doc: /* Convert the multibyte character CH to a byte.
-If the multibyte character does not represent a byte, return -1.  */)
-  (Lisp_Object ch)
-{
-  int cm;
-
-  CHECK_CHARACTER (ch);
-  cm = XFASTINT (ch);
-  if (cm < 256)
-    /* Can't distinguish a byte read from a unibyte buffer from
-       a latin1 char, so let's let it slide.  */
-    return ch;
-  else
-    {
-      int cu = CHAR_TO_BYTE_SAFE (cm);
-      return make_number (cu);
-    }
-}
-
-
 /* Return width (columns) of C considering the buffer display table DP. */
 
 static ptrdiff_t
@@ -632,7 +610,6 @@ syms_of_character (void)
   staticpro (&Vchar_unify_table);
   Vchar_unify_table = Qnil;
 
-  defsubr (&Smultibyte_char_to_unibyte);
   defsubr (&Schar_width);
   defsubr (&Sstring_width);
   defsubr (&Sstring);