Add bit_count SQL function

This function for bit and bytea counts the set bits in the bit or byte
string.  Internally, we use the existing popcount functionality.

For the name, after some discussion, we settled on bit_count, which
also exists with this meaning in MySQL, Java, and Python.

Author: David Fetter <david@fetter.org>
Discussion: https://www.postgresql.org/message-id/flat/20201230105535.GJ13234@fetter.org

doc/src/sgml/func.sgml

@@ -4010,6 +4010,28 @@ SELECT format('Testing %3$s, %2$s, %s', 'one', 'two', 'three');
      </thead>
 
      <tbody>
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>bit_count</primary>
+        </indexterm>
+        <indexterm>
+         <primary>popcount</primary>
+         <see>bit_count</see>
+        </indexterm>
+        <function>bit_count</function> ( <parameter>bytes</parameter> <type>bytea</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para>
+        Returns the number of bits set in the binary string (also known as
+        <quote>popcount</quote>).
+       </para>
+       <para>
+        <literal>bit_count('\x1234567890'::bytea)</literal>
+        <returnvalue>31</returnvalue>
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
@@ -4714,6 +4736,24 @@ SELECT format('Testing %3$s, %2$s, %s', 'one', 'two', 'three');
      </thead>
 
      <tbody>
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>bit_count</primary>
+        </indexterm>
+        <function>bit_count</function> ( <type>bit</type> )
+        <returnvalue>bigint</returnvalue>
+       </para>
+       <para>
+        Returns the number of bits set in the bit string (also known as
+        <quote>popcount</quote>).
+       </para>
+       <para>
+        <literal>bit_count(B'10111')</literal>
+        <returnvalue>4</returnvalue>
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>

src/backend/utils/adt/varbit.c

@@ -36,6 +36,7 @@
 #include "libpq/pqformat.h"
 #include "nodes/nodeFuncs.h"
 #include "nodes/supportnodes.h"
+#include "port/pg_bitutils.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
 #include "utils/varbit.h"
@@ -1201,6 +1202,19 @@ bit_overlay(VarBit *t1, VarBit *t2, int sp, int sl)
 	return result;
 }
 
+/*
+ * bit_count
+ *
+ * Returns the number of bits set in a bit string.
+ */
+Datum
+bit_bit_count(PG_FUNCTION_ARGS)
+{
+	VarBit	   *arg = PG_GETARG_VARBIT_P(0);
+
+	PG_RETURN_INT64(pg_popcount((char *) VARBITS(arg), VARBITBYTES(arg)));
+}
+
 /*
  * bitlength, bitoctetlength
  * Return the length of a bit string

src/backend/utils/adt/varlena.c

@@ -3440,6 +3440,17 @@ bytea_overlay(bytea *t1, bytea *t2, int sp, int sl)
 	return result;
 }
 
+/*
+ * bit_count
+ */
+Datum
+bytea_bit_count(PG_FUNCTION_ARGS)
+{
+	bytea	   *t1 = PG_GETARG_BYTEA_PP(0);
+
+	PG_RETURN_INT64(pg_popcount(VARDATA_ANY(t1), VARSIZE_ANY_EXHDR(t1)));
+}
+
 /*
  * byteapos -
  *	  Return the position of the specified substring.

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202103231
+#define CATALOG_VERSION_NO	202103232
 
 #endif

src/include/catalog/pg_proc.dat

@@ -1446,6 +1446,9 @@
 { oid => '752', descr => 'substitute portion of string',
   proname => 'overlay', prorettype => 'bytea',
   proargtypes => 'bytea bytea int4', prosrc => 'byteaoverlay_no_len' },
+{ oid => '8436', descr => 'number of set bits',
+  proname => 'bit_count', prorettype => 'int8', proargtypes => 'bytea',
+  prosrc => 'bytea_bit_count'},
 
 { oid => '725',
   proname => 'dist_pl', prorettype => 'float8', proargtypes => 'point line',
@@ -3876,6 +3879,9 @@
 { oid => '3033', descr => 'set bit',
   proname => 'set_bit', prorettype => 'bit', proargtypes => 'bit int4 int4',
   prosrc => 'bitsetbit' },
+{ oid => '8435', descr => 'number of set bits',
+  proname => 'bit_count', prorettype => 'int8', proargtypes => 'bit',
+  prosrc => 'bit_bit_count'},
 
 # for macaddr type support
 { oid => '436', descr => 'I/O',

src/test/regress/expected/bit.out

@@ -710,6 +710,19 @@ SELECT overlay(B'0101011100' placing '001' from 20);
  0101011100001
 (1 row)
 
+-- bit_count
+SELECT bit_count(B'0101011100'::bit(10));
+ bit_count 
+-----------
+         5
+(1 row)
+
+SELECT bit_count(B'1111111111'::bit(10));
+ bit_count 
+-----------
+        10
+(1 row)
+
 -- This table is intentionally left around to exercise pg_dump/pg_upgrade
 CREATE TABLE bit_defaults(
   b1 bit(4) DEFAULT '1001',

src/test/regress/expected/strings.out

@@ -2227,3 +2227,9 @@ SELECT encode(overlay(E'Th\\000omas'::bytea placing E'\\002\\003'::bytea from 5
  Th\000o\x02\x03
 (1 row)
 
+SELECT bit_count('\x1234567890'::bytea);
+ bit_count 
+-----------
+        31
+(1 row)
+

src/test/regress/sql/bit.sql

@@ -215,6 +215,10 @@ SELECT overlay(B'0101011100' placing '101' from 6);
 SELECT overlay(B'0101011100' placing '001' from 11);
 SELECT overlay(B'0101011100' placing '001' from 20);
 
+-- bit_count
+SELECT bit_count(B'0101011100'::bit(10));
+SELECT bit_count(B'1111111111'::bit(10));
+
 -- This table is intentionally left around to exercise pg_dump/pg_upgrade
 CREATE TABLE bit_defaults(
   b1 bit(4) DEFAULT '1001',

src/test/regress/sql/strings.sql

@@ -742,3 +742,5 @@ SELECT btrim(E'\\000trim\\000'::bytea, ''::bytea);
 SELECT encode(overlay(E'Th\\000omas'::bytea placing E'Th\\001omas'::bytea from 2),'escape');
 SELECT encode(overlay(E'Th\\000omas'::bytea placing E'\\002\\003'::bytea from 8),'escape');
 SELECT encode(overlay(E'Th\\000omas'::bytea placing E'\\002\\003'::bytea from 5 for 3),'escape');
+
+SELECT bit_count('\x1234567890'::bytea);