.\" .\" Copyright (c) 2025 Robert Clausecker <[email protected]> .\" .\" SPDX-License-Identifier: BSD-2-Clause .\" .Dd November 9, 2025 .Dt STDC_COUNT_ONES 3 .Os .Sh NAME .Nm stdc_count_ones .Nd count the ones in an integer .Sh SYNOPSIS .Lb libc .In stdbit.h .Ft unsigned int .Fn stdc_count_ones_uc "unsigned char value" .Ft unsigned int .Fn stdc_count_ones_us "unsigned short value" .Ft unsigned int .Fn stdc_count_ones_ui "unsigned int value" .Ft unsigned int .Fn stdc_count_ones_ul "unsigned long value" .Ft unsigned int .Fn stdc_count_ones_ull "unsigned long long value" .Ft unsigned int .Fn stdc_count_ones "value" .Sh DESCRIPTION The .Nm stdc_count_ones_ Ns Em type Ns () family of functions returns the number of bits set to\~1 in .Fa value , where .Fa value is of type .Va unsigned char , .Va unsigned short , .Va unsigned int , .Va unsigned long , or .Va unsigned long long for .Em type being .Sy uc , .Sy us , .Sy ui , .Sy ul , or .Sy ull respectively. This is also known as the .Dq population count (popcount) or .Dq Hamming weight operation. The .Fn stdc_count_ones "value" type-generic macro picks the appropriate .Nm stdc_count_ones_ Ns Em type Ns () function based on the type of .Fa value . .Sh RETURN VALUES Returns the number of bits set to\~1 in .Fa value . .Sh SEE ALSO .Xr bit_count 3 , .Xr stdbit 3 , .Xr stdc_count_zeros 3 , .Xr stdc_has_single_bit 3 .Sh STANDARDS The .Nm stdc_count_ones_ Ns Em type Ns () family of functions and the .Fn stdc_count_ones type-generic macro conform to .St -isoC-2023 . .Sh HISTORY The .Nm stdc_count_ones_ Ns Em type Ns () family of functions and the .Fn stdc_count_ones type-generic macro were added in .Fx 15.1. .Sh AUTHOR .An Robert Clausecker Aq Mt [email protected]
