1.\" 2.\" Copyright (c) 2025 Robert Clausecker <fuz@FreeBSD.org> 3.\" 4.\" SPDX-License-Identifier: BSD-2-Clause 5.\" 6.Dd November 9, 2025 7.Dt STDC_COUNT_ZEROS 3 8.Os 9.Sh NAME 10.Nm stdc_count_zeros 11.Nd count the zeros in an integer 12.Sh SYNOPSIS 13.Lb libc 14.In stdbit.h 15.Ft unsigned int 16.Fn stdc_count_zeros_uc "unsigned char value" 17.Ft unsigned int 18.Fn stdc_count_zeros_us "unsigned short value" 19.Ft unsigned int 20.Fn stdc_count_zeros_ui "unsigned int value" 21.Ft unsigned int 22.Fn stdc_count_zeros_ul "unsigned long value" 23.Ft unsigned int 24.Fn stdc_count_zeros_ull "unsigned long long value" 25.Ft unsigned int 26.Fn stdc_count_zeros "value" 27.Sh DESCRIPTION 28The 29.Nm stdc_count_zeros_ Ns Em type Ns () 30family of functions returns the number of bits set to\~0 in 31.Fa value , 32where 33.Fa value 34is of type 35.Va unsigned char , 36.Va unsigned short , 37.Va unsigned int , 38.Va unsigned long , 39or 40.Va unsigned long long 41for 42.Em type 43being 44.Sy uc , 45.Sy us , 46.Sy ui , 47.Sy ul , 48or 49.Sy ull 50respectively. 51This is also known as the 52.Dq population count 53(popcount) or 54.Dq Hamming weight 55of the complement of 56.Fa value . 57The 58.Fn stdc_count_zeros "value" 59type-generic macro picks the appropriate 60.Nm stdc_count_zeros_ Ns Em type Ns () 61function based on the type of 62.Fa value . 63.Sh RETURN VALUES 64Returns the number of bits set to\~0 in 65.Fa value . 66.Sh SEE ALSO 67.Xr stdbit 3 , 68.Xr stdc_count_ones 3 69.Sh STANDARDS 70The 71.Nm stdc_count_zeros_ Ns Em type Ns () 72family of functions and the 73.Fn stdc_count_zeros 74type-generic macro conform to 75.St -isoC-2023 . 76.Sh HISTORY 77The 78.Nm stdc_count_zeros_ Ns Em type Ns () 79family of functions and the 80.Fn stdc_count_zeros 81type-generic macro were added in 82.Fx 15.1. 83.Sh AUTHOR 84.An Robert Clausecker Aq Mt fuz@FreeBSD.org 85