scratch/hash-table-perf ef0323e9029 30/35: Adapt hash functions to produce a hash_hash_t eventually

[Mattias Engdegård]

branch: scratch/hash-table-perf
commit ef0323e9029dd8612a8fc5144b0a243245465bcd
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Adapt hash functions to produce a hash_hash_t eventually
    
    This eliminates some useless and information-destroying intermediate
    hash reduction steps.
    
    We still use EMACS_UINT for most of the actual hashing steps before
    producing the final value; this may be slightly wasteful on 32-bit
    platforms with 64-bit EMACS_UINT.
    
    * src/fns.c (reduce_emacs_uint_to_hash_hash): New.
    (hashfn_eq, hashfn_equal, hashfn_user_defined): Reduce return values
    to hash_hash_t.
    (sxhash_string): Remove.  Caller changed to hash_string.
    (sxhash_float, sxhash_list, sxhash_vector, sxhash_bool_vector)
    (sxhash_bignum): Remove wasteful calls to SXHASH_REDUCE.
    (hash_hash_to_fixnum): New.
    (Fsxhash_eq, Fsxhash_eql, Fsxhash_equal)
    (Fsxhash_equal_including_properties): Convert return values to fixnum.
---
 src/fns.c | 77 ++++++++++++++++++++++++++++++++++-----------------------------
 1 file changed, 42 insertions(+), 35 deletions(-)

diff --git a/src/fns.c b/src/fns.c
index 4acef3f5682..7eb780cb839 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -4452,6 +4452,16 @@ cmpfn_user_defined (Lisp_Object key1, Lisp_Object key2,
   return hash_table_user_defined_call (ARRAYELTS (args), args, h);
 }
 
+/* Reduce an EMACS_UINT hash value to hash_hash_t.  */
+static inline hash_hash_t
+reduce_emacs_uint_to_hash_hash (EMACS_UINT x)
+{
+  verify (sizeof x <= 2 * sizeof (hash_hash_t));
+  return (sizeof x == sizeof (hash_hash_t)
+         ? x
+         : x ^ (x >> (8 * (sizeof x - sizeof (hash_hash_t)))));
+}
+
 /* Ignore H and return a hash code for KEY which uses 'eq' to compare keys.  */
 
 static hash_hash_t
@@ -4459,21 +4469,18 @@ hashfn_eq (Lisp_Object key, struct Lisp_Hash_Table *h)
 {
   if (symbols_with_pos_enabled && SYMBOL_WITH_POS_P (key))
     key = SYMBOL_WITH_POS_SYM (key);
-  return XHASH (key) ^ XTYPE (key);
+  return reduce_emacs_uint_to_hash_hash (XHASH (key) ^ XTYPE (key));
 }
 
-/* Ignore H and return a hash code for KEY which uses 'equal' to compare keys.
-   The hash code is at most INTMASK.  */
-
+/* Ignore H and return a hash code for KEY which uses 'equal' to
+   compare keys.  */
 static hash_hash_t
 hashfn_equal (Lisp_Object key, struct Lisp_Hash_Table *h)
 {
-  return sxhash (key);
+  return reduce_emacs_uint_to_hash_hash (sxhash (key));
 }
 
-/* Ignore H and return a hash code for KEY which uses 'eql' to compare keys.
-   The hash code is at most INTMASK.  */
-
+/* Ignore H and return a hash code for KEY which uses 'eql' to compare keys.  
*/
 static hash_hash_t
 hashfn_eql (Lisp_Object key, struct Lisp_Hash_Table *h)
 {
@@ -4489,7 +4496,8 @@ hashfn_user_defined (Lisp_Object key, struct 
Lisp_Hash_Table *h)
 {
   Lisp_Object args[] = { h->test->user_hash_function, key };
   Lisp_Object hash = hash_table_user_defined_call (ARRAYELTS (args), args, h);
-  return FIXNUMP (hash) ? XUFIXNUM(hash) : sxhash (hash);
+  return reduce_emacs_uint_to_hash_hash (FIXNUMP (hash)
+                                        ? XUFIXNUM(hash) : sxhash (hash));
 }
 
 struct hash_table_test const
@@ -5042,16 +5050,6 @@ hash_string (char const *ptr, ptrdiff_t len)
   return hash;
 }
 
-/* Return a hash for string PTR which has length LEN.  The hash
-   code returned is at most INTMASK.  */
-
-static EMACS_UINT
-sxhash_string (char const *ptr, ptrdiff_t len)
-{
-  EMACS_UINT hash = hash_string (ptr, len);
-  return SXHASH_REDUCE (hash);
-}
-
 /* Return a hash for the floating point value VAL.  */
 
 static EMACS_UINT
@@ -5061,7 +5059,7 @@ sxhash_float (double val)
   union double_and_words u = { .val = val };
   for (int i = 0; i < WORDS_PER_DOUBLE; i++)
     hash = sxhash_combine (hash, u.word[i]);
-  return SXHASH_REDUCE (hash);
+  return hash;
 }
 
 /* Return a hash for list LIST.  DEPTH is the current depth in the
@@ -5088,7 +5086,7 @@ sxhash_list (Lisp_Object list, int depth)
       hash = sxhash_combine (hash, hash2);
     }
 
-  return SXHASH_REDUCE (hash);
+  return hash;
 }
 
 
@@ -5108,7 +5106,7 @@ sxhash_vector (Lisp_Object vec, int depth)
       hash = sxhash_combine (hash, hash2);
     }
 
-  return SXHASH_REDUCE (hash);
+  return hash;
 }
 
 /* Return a hash for bool-vector VECTOR.  */
@@ -5124,7 +5122,7 @@ sxhash_bool_vector (Lisp_Object vec)
   for (i = 0; i < n; ++i)
     hash = sxhash_combine (hash, bool_vector_data (vec)[i]);
 
-  return SXHASH_REDUCE (hash);
+  return hash;
 }
 
 /* Return a hash for a bignum.  */
@@ -5139,19 +5137,18 @@ sxhash_bignum (Lisp_Object bignum)
   for (i = 0; i < nlimbs; ++i)
     hash = sxhash_combine (hash, mpz_getlimbn (*n, i));
 
-  return SXHASH_REDUCE (hash);
+  return hash;
 }
 
-
-/* Return a hash code for OBJ.  DEPTH is the current depth in the Lisp
-   structure.  Value is an unsigned integer clipped to INTMASK.  */
-
 EMACS_UINT
 sxhash (Lisp_Object obj)
 {
   return sxhash_obj (obj, 0);
 }
 
+/* Return a hash code for OBJ.  DEPTH is the current depth in the Lisp
+   structure.  */
+
 static EMACS_UINT
 sxhash_obj (Lisp_Object obj, int depth)
 {
@@ -5167,7 +5164,7 @@ sxhash_obj (Lisp_Object obj, int depth)
       return XHASH (obj);
 
     case Lisp_String:
-      return sxhash_string (SSDATA (obj), SBYTES (obj));
+      return hash_string (SSDATA (obj), SBYTES (obj));
 
     case Lisp_Vectorlike:
       {
@@ -5194,7 +5191,7 @@ sxhash_obj (Lisp_Object obj, int depth)
              = XMARKER (obj)->buffer ? XMARKER (obj)->bytepos : 0;
            EMACS_UINT hash
              = sxhash_combine ((intptr_t) XMARKER (obj)->buffer, bytepos);
-           return SXHASH_REDUCE (hash);
+           return hash;
          }
        else if (pvec_type == PVEC_BOOL_VECTOR)
          return sxhash_bool_vector (obj);
@@ -5203,7 +5200,7 @@ sxhash_obj (Lisp_Object obj, int depth)
            EMACS_UINT hash = OVERLAY_START (obj);
            hash = sxhash_combine (hash, OVERLAY_END (obj));
            hash = sxhash_combine (hash, sxhash_obj (XOVERLAY (obj)->plist, 
depth));
-           return SXHASH_REDUCE (hash);
+           return hash;
          }
        else if (symbols_with_pos_enabled && pvec_type == PVEC_SYMBOL_WITH_POS)
          return sxhash_obj (XSYMBOL_WITH_POS (obj)->sym, depth + 1);
@@ -5239,6 +5236,15 @@ collect_interval (INTERVAL interval, Lisp_Object 
collector)
                            Lisp Interface
  ***********************************************************************/
 
+/* Reduce X to a Lisp fixnum.  */
+static inline Lisp_Object
+hash_hash_to_fixnum (hash_hash_t x)
+{
+  return make_ufixnum (FIXNUM_BITS < 8 * sizeof x
+                      ? (x ^ x >> (8 * sizeof x - FIXNUM_BITS)) & INTMASK
+                      : x);
+}
+
 DEFUN ("sxhash-eq", Fsxhash_eq, Ssxhash_eq, 1, 1, 0,
        doc: /* Return an integer hash code for OBJ suitable for `eq'.
 If (eq A B), then (= (sxhash-eq A) (sxhash-eq B)).
@@ -5246,7 +5252,7 @@ If (eq A B), then (= (sxhash-eq A) (sxhash-eq B)).
 Hash codes are not guaranteed to be preserved across Emacs sessions.  */)
   (Lisp_Object obj)
 {
-  return make_ufixnum (hashfn_eq (obj, NULL));
+  return hash_hash_to_fixnum (hashfn_eq (obj, NULL));
 }
 
 DEFUN ("sxhash-eql", Fsxhash_eql, Ssxhash_eql, 1, 1, 0,
@@ -5257,7 +5263,7 @@ isn't necessarily true.
 Hash codes are not guaranteed to be preserved across Emacs sessions.  */)
   (Lisp_Object obj)
 {
-  return make_ufixnum (hashfn_eql (obj, NULL));
+  return hash_hash_to_fixnum (hashfn_eql (obj, NULL));
 }
 
 DEFUN ("sxhash-equal", Fsxhash_equal, Ssxhash_equal, 1, 1, 0,
@@ -5268,7 +5274,7 @@ opposite isn't necessarily true.
 Hash codes are not guaranteed to be preserved across Emacs sessions.  */)
   (Lisp_Object obj)
 {
-  return make_ufixnum (hashfn_equal (obj, NULL));
+  return hash_hash_to_fixnum (hashfn_equal (obj, NULL));
 }
 
 DEFUN ("sxhash-equal-including-properties", Fsxhash_equal_including_properties,
@@ -5283,6 +5289,7 @@ Hash codes are not guaranteed to be preserved across 
Emacs sessions.  */)
 {
   if (STRINGP (obj))
     {
+      /* FIXME: This is very wasteful.  We needn't cons at all.  */
       Lisp_Object collector = Fcons (Qnil, Qnil);
       traverse_intervals (string_intervals (obj), 0, collect_interval,
                          collector);
@@ -5292,7 +5299,7 @@ Hash codes are not guaranteed to be preserved across 
Emacs sessions.  */)
                                         sxhash (CDR (collector)))));
     }
 
-  return make_ufixnum (hashfn_equal (obj, NULL));
+  return hash_hash_to_fixnum (hashfn_equal (obj, NULL));
 }