Commit 185f3334 authored by Mark Oteiza's avatar Mark Oteiza

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.
parent 20a09de9
......@@ -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
@cindex popcount
@cindex Hamming weight
@cindex counting set bits
@defun logcount integer
This function returns the @dfn{Hamming weight} of @var{integer}: the
number of ones in the binary representation of @var{integer}.
@example
(logcount 42) ; 42 = #b101010
@result{} 3
@end example
@end defun
@node Math Functions
@section Standard Mathematical Functions
@cindex transcendental functions
......
......@@ -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
......
......@@ -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);
......
......@@ -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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