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[Emacs-diffs] master 185f333: Add logcount (Bug#22689)
From: |
Mark Oteiza |
Subject: |
[Emacs-diffs] master 185f333: Add logcount (Bug#22689) |
Date: |
Sat, 30 Sep 2017 14:17:20 -0400 (EDT) |
branch: master
commit 185f33340680d918a95ff704a8f7e2d9e1a6f0ca
Author: Mark Oteiza <address@hidden>
Commit: Mark Oteiza <address@hidden>
Add logcount (Bug#22689)
* doc/lispref/numbers.texi (Bitwise Operations): Add documentation.
* etc/NEWS: Mention.
* src/data.c (logcount32, logcount64): New functions.
(logcount): New Lisp function.
(syms_of_data): Declare it.
* test/src/data-tests.el (data-tests-popcnt, data-tests-logcount): New
test.
---
doc/lispref/numbers.texi | 13 +++++++++++
etc/NEWS | 3 +++
src/data.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++
test/src/data-tests.el | 13 +++++++++++
4 files changed, 90 insertions(+)
diff --git a/doc/lispref/numbers.texi b/doc/lispref/numbers.texi
index 3fdc941..5058063 100644
--- a/doc/lispref/numbers.texi
+++ b/doc/lispref/numbers.texi
@@ -1107,6 +1107,19 @@ bit is one in the result if, and only if, the @var{n}th
bit is zero in
@end example
@end defun
address@hidden popcount
address@hidden Hamming weight
address@hidden counting set bits
address@hidden logcount integer
+This function returns the @dfn{Hamming weight} of @var{integer}: the
+number of ones in the binary representation of @var{integer}.
+
address@hidden
+(logcount 42) ; 42 = #b101010
+ @result{} 3
address@hidden example
address@hidden defun
+
@node Math Functions
@section Standard Mathematical Functions
@cindex transcendental functions
diff --git a/etc/NEWS b/etc/NEWS
index 238c7b7..8fbc354 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -31,6 +31,9 @@ When you add a new item, use the appropriate mark if you are
sure it applies,
* Changes in Emacs 27.1
++++
+** New function 'logcount' calculates an integer's Hamming weight.
+
* Editing Changes in Emacs 27.1
diff --git a/src/data.c b/src/data.c
index e070be6..b595e3f 100644
--- a/src/data.c
+++ b/src/data.c
@@ -3069,6 +3069,66 @@ usage: (logxor &rest INTS-OR-MARKERS) */)
return arith_driver (Alogxor, nargs, args);
}
+#if GNUC_PREREQ (4, 1, 0)
+#define HAVE_BUILTIN_POPCOUNTLL
+#endif
+
+#ifndef HAVE_BUILTIN_POPCOUNTLL
+static uint32_t
+logcount32 (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
+logcount64 (uint64_t b)
+{
+ b -= (b >> 1) & 0x5555555555555555ULL;
+ b = (b & 0x3333333333333333ULL) + ((b >> 2) & 0x3333333333333333ULL);
+ b = (b + (b >> 4)) & 0x0f0f0f0f0f0f0f0fULL;
+ return (b * 0x0101010101010101ULL) >> 56;
+}
+#endif /* HAVE_BUILTIN_POPCOUNTLL */
+
+DEFUN ("logcount", Flogcount, Slogcount, 1, 1, 0,
+ doc: /* Return population count of VALUE.
+If VALUE is negative, the count is of its two's complement representation. */)
+ (register Lisp_Object value)
+{
+ Lisp_Object res;
+ EMACS_UINT v;
+
+ CHECK_NUMBER (value);
+
+ v = XUINT (value);
+#ifdef HAVE_BUILTIN_POPCOUNTLL
+ if (v <= UINT_MAX)
+ XSETINT (res, __builtin_popcount (v));
+ else if (v <= ULONG_MAX)
+ XSETINT (res, __builtin_popcountl (v));
+ else if (v <= ULONG_LONG_MAX)
+ XSETINT (res, __builtin_popcountll (v));
+#else /* HAVE_BUILTIN_POPCOUNTLL */
+ if (v <= UINT_MAX)
+ XSETINT (res, logcount32 (v));
+ else if (v <= ULONG_MAX || v <= ULONG_LONG_MAX)
+ XSETINT (res, logcount64 (v));
+#endif /* HAVE_BUILTIN_POPCOUNTLL */
+ else
+ {
+ unsigned int count;
+ for (count = 0; v; count++)
+ {
+ v &= v - 1;
+ }
+ XSETINT (res, count);
+ }
+ return res;
+}
+
static Lisp_Object
ash_lsh_impl (Lisp_Object value, Lisp_Object count, bool lsh)
{
@@ -3856,6 +3916,7 @@ syms_of_data (void)
defsubr (&Slogand);
defsubr (&Slogior);
defsubr (&Slogxor);
+ defsubr (&Slogcount);
defsubr (&Slsh);
defsubr (&Sash);
defsubr (&Sadd1);
diff --git a/test/src/data-tests.el b/test/src/data-tests.el
index 8de8c14..d1154cc 100644
--- a/test/src/data-tests.el
+++ b/test/src/data-tests.el
@@ -107,6 +107,19 @@
(should (isnan (min 1.0 0.0e+NaN)))
(should (isnan (min 1.0 0.0e+NaN 1.1))))
+(defun data-tests-popcnt (byte)
+ "Calculate the Hamming weight of BYTE."
+ (setq byte (- byte (logand (lsh byte -1) #x55555555)))
+ (setq byte (+ (logand byte #x33333333) (logand (lsh byte -2) #x33333333)))
+ (lsh (* (logand (+ byte (lsh byte -4)) #x0f0f0f0f) #x01010101) -24))
+
+(ert-deftest data-tests-logcount ()
+ (should (cl-loop for n in (number-sequence 0 255)
+ always (= (logcount n) (data-tests-popcnt n))))
+ ;; https://oeis.org/A000120
+ (should (= 11 (logcount 9727)))
+ (should (= 8 (logcount 9999))))
+
;; Bool vector tests. Compactly represent bool vectors as hex
;; strings.
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