New primitives sxhash-eq, sxhash-eql

* doc/lispref/hash.texi (Defining Hash), etc/NEWS: Document this.
* lisp/emacs-lisp/byte-opt.el (side-effect-free-fns):
Add sxhash-equal, sxhash-eq, sxhash-eql.
* lisp/subr.el (sxhash): Now an alias for sxhash-equal.
* src/fns.c (Fsxhash_eq, Fsxhash_eql): New functions.n

doc/lispref/hash.texi

@@ -268,18 +268,43 @@ under the property @code{hash-table-test}; the property value's form is
 @code{(@var{test-fn} @var{hash-fn})}.
 @end defun
 
-@defun sxhash obj
+@defun sxhash-equal obj
 This function returns a hash code for Lisp object @var{obj}.
 This is an integer which reflects the contents of @var{obj}
 and the other Lisp objects it points to.
 
-If two objects @var{obj1} and @var{obj2} are equal, then @code{(sxhash
+If two objects @var{obj1} and @var{obj2} are @code{equal}, then
-@var{obj1})} and @code{(sxhash @var{obj2})} are the same integer.
+@code{(sxhash-equal @var{obj1})} and @code{(sxhash-equal @var{obj2})}
+are the same integer.
 
-If the two objects are not equal, the values returned by @code{sxhash}
+If the two objects are not @code{equal}, the values returned by
-are usually different, but not always; once in a rare while, by luck,
+@code{sxhash-equal} are usually different, but not always; once in a
-you will encounter two distinct-looking objects that give the same
+rare while, by luck, you will encounter two distinct-looking objects
-result from @code{sxhash}.
+that give the same result from @code{sxhash-equal}.
+
+@b{Common Lisp note:} In Common Lisp a similar function is called
+@code{sxhash}.  Emacs provides this name as a compatibility alias for
+@code{sxhash-equal}.
+@end defun
+
+@defun sxhash-eq obj
+This function returns a hash code for Lisp object @var{obj}.  Its
+result reflects identity of @var{obj}, but not its contents.
+
+If two objects @var{obj1} and @var{obj2} are @code{eq}, then
+@code{(xhash @var{obj1})} and @code{(xhash @var{obj2})} are the same
+integer.
+@end defun
+
+@defun sxhash-eql obj
+This function returns a hash code for Lisp object @var{obj} suitable
+for @code{eql} comparison.  I.e. it reflects identity of @var{obj}
+except for the case where the object is a float number, in which case
+hash code is generated for the value.
+
+If two objects @var{obj1} and @var{obj2} are @code{eql}, then
+@code{(xhash @var{obj1})} and @code{(xhash @var{obj2})} are the same
+integer.
 @end defun
 
   This example creates a hash table whose keys are strings that are
@@ -289,7 +314,7 @@ compared case-insensitively.
 (defun case-fold-string= (a b)
   (eq t (compare-strings a nil nil b nil nil t)))
 (defun case-fold-string-hash (a)
-  (sxhash (upcase a)))
+  (sxhash-equal (upcase a)))
 
 (define-hash-table-test 'case-fold
   'case-fold-string= 'case-fold-string-hash)
@@ -302,7 +327,7 @@ predefined test value @code{equal}.  The keys can be any Lisp object,
 and equal-looking objects are considered the same key.
 
 @example
-(define-hash-table-test 'contents-hash 'equal 'sxhash)
+(define-hash-table-test 'contents-hash 'equal 'sxhash-equal)
 
 (make-hash-table :test 'contents-hash)
 @end example

etc/NEWS

@@ -217,6 +217,17 @@ outermost parenthesis.
 ** The function 'redirect-debugging-output' now works on platforms
 other than GNU/Linux.
 
++++
+** New functions 'sxhash-eq' and 'sxhash-eql' return hash codes of a
+Lisp object suitable for use with 'eq' and 'eql' correspondingly.  If
+two objects are 'eq' ('eql'), then the result of 'sxhash-eq'
+('sxhash-eql') on them will be the same.
+
++++
+** Function 'sxhash' has been renamed to 'sxhash-equal' for
+consistency with the new functions.  For compatibility, 'sxhash'
+remains as an alias to 'sxhash-equal'.
+
 
 * Changes in Emacs 25.2 on Non-Free Operating Systems
 

lisp/emacs-lisp/byte-opt.el

@@ -1209,8 +1209,9 @@
 	 radians-to-degrees rassq rassoc read-from-string regexp-quote
 	 region-beginning region-end reverse round
 	 sin sqrt string string< string= string-equal string-lessp string-to-char
-	 string-to-int string-to-number substring sxhash symbol-function
+	 string-to-int string-to-number substring
-	 symbol-name symbol-plist symbol-value string-make-unibyte
+	 sxhash sxhash-equal sxhash-eq sxhash-eql
+	 symbol-function symbol-name symbol-plist symbol-value string-make-unibyte
 	 string-make-multibyte string-as-multibyte string-as-unibyte
 	 string-to-multibyte
 	 tan truncate

lisp/subr.el

@@ -66,6 +66,7 @@ For more information, see Info node `(elisp)Declaring Functions'."
 ;;;; Basic Lisp macros.
 
 (defalias 'not 'null)
+(defalias 'sxhash 'sxhash-equal)
 
 (defmacro noreturn (form)
   "Evaluate FORM, expecting it not to return.

src/fns.c

@@ -4447,8 +4447,26 @@ sxhash (Lisp_Object obj, int depth)
 			    Lisp Interface
  ***********************************************************************/
 
+DEFUN ("sxhash-eq", Fsxhash_eq, Ssxhash_eq, 1, 1, 0,
+       doc: /* Compute identity hash code for OBJ and return it as integer.
+In other words, hash codes of two non-`eq' lists will be (most likely)
+different, even if the lists contain the same elements. */)
+  (Lisp_Object obj)
+{
+  return make_number (hashfn_eq (NULL, obj));
+}
 
-DEFUN ("sxhash", Fsxhash, Ssxhash, 1, 1, 0,
+DEFUN ("sxhash-eql", Fsxhash_eql, Ssxhash_eql, 1, 1, 0,
+       doc: /* Compute identity hash code for OBJ and return it as integer.
+In comparison to `sxhash-eq', it is also guaranteed that hash codes
+of equal float numbers will be the same, even if the numbers are not
+the same Lisp object. */)
+  (Lisp_Object obj)
+{
+  return make_number (hashfn_eql (NULL, obj));
+}
+
+DEFUN ("sxhash-equal", Fsxhash_equal, Ssxhash_equal, 1, 1, 0,
        doc: /* Compute a hash code for OBJ and return it as integer.  */)
   (Lisp_Object obj)
 {
@@ -5066,7 +5084,9 @@ syms_of_fns (void)
   DEFSYM (Qkey_or_value, "key-or-value");
   DEFSYM (Qkey_and_value, "key-and-value");
 
-  defsubr (&Ssxhash);
+  defsubr (&Ssxhash_eq);
+  defsubr (&Ssxhash_eql);
+  defsubr (&Ssxhash_equal);
   defsubr (&Smake_hash_table);
   defsubr (&Scopy_hash_table);
   defsubr (&Shash_table_count);