Subject: [PATCH] Add logcount

From: Mark Oteiza <[email-masked]>
Date: Fri, 29 Sep 2017 13:41:34 -0400

Hi,

I made an attempt implementing this:

diff --git a/src/data.c b/src/data.c
index e070be6c20..1332173dcd 100644
--- a/src/data.c
+++ b/src/data.c
@@ -3069,6 +3069,57 @@ usage: (logxor &rest INTS-OR-MARKERS)  */)
   return arith_driver (Alogxor, nargs, args);
 }
 
+#if defined (__POPCNT__) && defined (__GNUC__) && (__GNUC__> 4 || (__GNUC__== 4 && __GNUC_MINOR__> 1))
+#define HAVE_BUILTIN_POPCOUNTLL
+#endif
+
+static uint32_t
+bitcount32 (uint32_t b)
+{
+  b -= (b >> 1) & 0x55555555;
+  b = (b & 0x33333333) + ((b >> 2) & 0x33333333);
+  b = (b + (b >> 4)) & 0x0f0f0f0f;
+  return (b * 0x01010101) >> 24;
+}  
+
+static uint64_t
+bitcount64 (uint64_t b)
+{
+  b -= (b >> 1) & 0x5555555555555555;
+  b = (b & 0x3333333333333333) + ((b >> 2) & 0x3333333333333333);
+  b = (b + (b >> 4)) & 0x0f0f0f0f0f0f0f0f;
+  return (b * 0x0101010101010101) >> 56;
+}
+
+DEFUN ("logcount", Flogcount, Slogcount, 1, 1, 0,
+       doc: /* Return population count of VALUE. */)
+  (register Lisp_Object value)
+{
+  Lisp_Object res;
+
+  CHECK_NUMBER (value);
+
+#ifdef HAVE_BUILTIN_POPCOUNTLL
+  XSETINT (res, __builtin_popcount (XUINT (value)));
+#else  /* HAVE_BUILTIN_POPCOUNTLL */
+  if (XINT (value) <= UINT_MAX)
+    XSETINT (res, bitcount32 (XUINT (value)));
+  else if (XINT (value) <= ULONG_MAX)
+    XSETINT (res, bitcount64 (XUINT (value)));
+  else
+    {
+      int count;
+      EMACS_UINT v = XUINT (value);
+      for (count = 0; v; count++)
+        {
+          v &= v - 1;
+        }
+      XSETINT (res, v);
+    }
+#endif /* HAVE_BUILTIN_POPCOUNTLL */
+  return res;
+}
+
 static Lisp_Object
 ash_lsh_impl (Lisp_Object value, Lisp_Object count, bool lsh)
 {
@@ -3856,6 +3907,7 @@ syms_of_data (void)
   defsubr (&Slogand);
   defsubr (&Slogior);
   defsubr (&Slogxor);
+  defsubr (&Slogcount);
   defsubr (&Slsh);
   defsubr (&Sash);
   defsubr (&Sadd1);