Reject attempts to clear pure strings

* src/fns.c (Ffillarray, Fclear_string):
Add CHECK_IMPURE here, to be consistent with Faset etc.
(Ffillarray): Prefer memset when the fill is a single byte.

1 files changed, 32 insertions, 19 deletions

diff --git a/src/fns.c b/src/fns.c
index 301bd59ab90..b2f84b202de 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -2508,26 +2508,36 @@ ARRAY is a vector, string, char-table, or bool-vector.  */)
     }
   else if (STRINGP (array))
     {
-      register unsigned char *p = SDATA (array);
-      int charval;
+      unsigned char *p = SDATA (array);
       CHECK_CHARACTER (item);
-      charval = XFIXNAT (item);
+      int charval = XFIXNAT (item);
       size = SCHARS (array);
-      if (STRING_MULTIBYTE (array))
+      if (size != 0)
         {
+          CHECK_IMPURE (array, XSTRING (array));
           unsigned char str[MAX_MULTIBYTE_LENGTH];
-          int len = CHAR_STRING (charval, str);
-          ptrdiff_t size_byte = SBYTES (array);
-          ptrdiff_t product;
+          int len;
+          if (STRING_MULTIBYTE (array))
+            len = CHAR_STRING (charval, str);
+          else
+            {
+              str[0] = charval;
+              len = 1;
+            }
 
-          if (INT_MULTIPLY_WRAPV (size, len, &product) || product != size_byte)
-            error ("Attempt to change byte length of a string");
-          for (idx = 0; idx < size_byte; idx++)
-            *p++ = str[idx % len];
+          ptrdiff_t size_byte = SBYTES (array);
+          if (len == 1 && size == size_byte)
+            memset (p, str[0], size);
+          else
+            {
+              ptrdiff_t product;
+              if (INT_MULTIPLY_WRAPV (size, len, &product)
+                  || product != size_byte)
+                error ("Attempt to change byte length of a string");
+              for (idx = 0; idx < size_byte; idx++)
+                *p++ = str[idx % len];
+            }
         }
-      else
-        for (idx = 0; idx < size; idx++)
-          p[idx] = charval;
     }
   else if (BOOL_VECTOR_P (array))
     return bool_vector_fill (array, item);
@@ -2542,12 +2552,15 @@ DEFUN ("clear-string", Fclear_string, Sclear_string,
 This makes STRING unibyte and may change its length.  */)
   (Lisp_Object string)
 {
-  ptrdiff_t len;
   CHECK_STRING (string);
-  len = SBYTES (string);
-  memset (SDATA (string), 0, len);
-  STRING_SET_CHARS (string, len);
-  STRING_SET_UNIBYTE (string);
+  ptrdiff_t len = SBYTES (string);
+  if (len != 0 || STRING_MULTIBYTE (string))
+    {
+      CHECK_IMPURE (string, XSTRING (string));
+      memset (SDATA (string), 0, len);
+      STRING_SET_CHARS (string, len);
+      STRING_SET_UNIBYTE (string);
+    }
   return Qnil;
 }