Editing Hamming weight (section)

== Language support ==
Some C compilers provide intrinsic functions that provide bit counting facilities. For example, [[GNU Compiler Collection|GCC]] (since version 3.4 in April 2004) includes a builtin function <code>__builtin_popcount</code> that will use a processor instruction if available or an efficient library implementation otherwise.<ref name="GCC"/> [[LLVM|LLVM-GCC]] has included this function since version 1.5 in June 2005.<ref name="LLVM"/>

In the [[C++ Standard Library]], the bit-array data structure <code>bitset</code> has a <code>count()</code> method that counts the number of bits that are set. In [[C++20]], a new header <code><bit></code> was added, containing functions <code>std::popcount</code> and <code>std::has_single_bit</code>, taking arguments of unsigned integer types.

In Java, the growable bit-array data structure {{Javadoc:SE|java/util|BitSet}} has a {{Javadoc:SE|java/util|BitSet|cardinality()}} method that counts the number of bits that are set. In addition, there are {{Javadoc:SE|java/lang|Integer|bitCount(int)}} and {{Javadoc:SE|java/lang|Long|bitCount(long)}} functions to count bits in primitive 32-bit and 64-bit integers, respectively. Also, the {{Javadoc:SE|java/math|BigInteger}} arbitrary-precision integer class also has a {{Javadoc:SE|java/math|BigInteger|bitCount()}} method that counts bits.

In [[Python (programming language)|Python]], the <code>int</code> type has a <code>bit_count()</code> method to count the number of bits set. This functionality was introduced in Python 3.10, released in October 2021.<ref>{{cite web |title=What's New In Python 3.10 |url=https://docs.python.org/3.10/whatsnew/3.10.html |website=python.org}}</ref>

In [[Common Lisp]], the function <code>logcount</code>, given a non-negative integer, returns the number of 1 bits. (For negative integers it returns the number of 0 bits in 2's complement notation.) In either case the integer can be a BIGNUM.

Starting in [[Glasgow Haskell Compiler|GHC]] 7.4, the [[Haskell (programming language)|Haskell]] base package has a <code>popCount</code> function available on all types that are instances of the <code>Bits</code> class (available from the <code>Data.Bits</code> module).<ref name="GHC"/>

[[MySQL]] version of [[SQL]] language provides <code>BIT_COUNT()</code> as a standard function.<ref name="MySQL_50"/>

[[Fortran 2008]] has the standard, intrinsic, elemental function <code>popcnt</code> returning the number of nonzero bits within an integer (or integer array).<ref name="Metcalf_2011"/>

Some programmable scientific pocket calculators feature special commands to calculate the number of set bits, e.g. <code>#B</code> on the [[HP-16C]]<ref name="HP-16C_1982"/><ref name="Schwartz_Grevelle_2003"/> and [[WP&nbsp;43S]],<ref name="Bonin_2019_OG"/><ref name="Bonin_2019_RG"/> <code>#BITS</code><ref name="Martin_McClure_2015"/><ref name="Martin_2015"/> or <code>BITSUM</code><ref name="Thörngren_2017"/><ref name="Thörngren_2017_2"/> on HP-16C emulators, and <code>nBITS</code> on the [[WP&nbsp;34S]].<ref name="Bonin_2012"/><ref name="Bonin_2015"/>

[[FreePascal]] implements popcnt since version 3.0.<ref name="FPC docs"/>