STDC_COUNT_ONES(3)     FreeBSD Library Functions Manual     STDC_COUNT_ONES(3)

NAME

     stdc_count_ones - count the ones in an integer

SYNOPSIS

     /* -lc */
     #include <stdbit.h>

     unsigned int
     stdc_count_ones_uc(unsigned char value);

     unsigned int
     stdc_count_ones_us(unsigned short value);

     unsigned int
     stdc_count_ones_ui(unsigned int value);

     unsigned int
     stdc_count_ones_ul(unsigned long value);

     unsigned int
     stdc_count_ones_ull(unsigned long long value);

     unsigned int
     stdc_count_ones(value);

DESCRIPTION

     The stdc_count_ones_type() family of functions returns the number of bits
     set to 1 in value, where value is of type unsigned char, unsigned short,
     unsigned int, unsigned long, or unsigned long long for type being uc, us,
     ui, ul, or ull respectively.  This is also known as the "population
     count" (popcount) or "Hamming weight" operation.  The
     stdc_count_ones(value) type-generic macro picks the appropriate
     stdc_count_ones_type() function based on the type of value.

RETURN VALUES

     Returns the number of bits set to 1 in value.

SEE ALSO

     bit_count(3), stdbit(3), stdc_count_zeros(3), stdc_has_single_bit(3)

STANDARDS

     The stdc_count_ones_type() family of functions and the stdc_count_ones()
     type-generic macro conform to ISO/IEC 9899:2024 ("ISO C23").

HISTORY

     The stdc_count_ones_type() family of functions and the stdc_count_ones()
     type-generic macro were added in FreeBSD 15.1.

AUTHOR

     Robert Clausecker <fuz@FreeBSD.org>

FreeBSD 15.1-STABLE-HBSD       November 9, 2025             STDC_COUNT_ONES(3)