NAME
stdc_count_ones – count the ones in an integer
SYNOPSIS
Standard C Library (libc, -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.
AUTHORS
Robert Clausecker ⟨[email protected]⟩