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_BIT_FLOOR 3 8.Os 9.Sh NAME 10.Nm stdc_bit_floor 11.Nd round down to the previous power of\~2 12.Sh SYNOPSIS 13.Lb libc 14.In stdbit.h 15.Ft unsigned char 16.Fn stdc_bit_floor_uc "unsigned char value" 17.Ft unsigned short 18.Fn stdc_bit_floor_us "unsigned short value" 19.Ft unsigned int 20.Fn stdc_bit_floor_ui "unsigned int value" 21.Ft unsigned long 22.Fn stdc_bit_floor_ul "unsigned long value" 23.Ft unsigned long long 24.Fn stdc_bit_floor_ull "unsigned long long value" 25.Ft typeof Ns Pq Em value 26.Fn stdc_bit_floor "value" 27.Sh DESCRIPTION 28The 29.Nm stdc_bit_floor_ Ns Em type Ns () 30family of functions rounds 31.Fa value 32down to the previous power of\~2, where 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. 51The 52.Fn stdc_bit_floor "value" 53type-generic macro picks the appropriate 54.Nm stdc_bit_floor_ Ns Em type Ns () 55function based on the type of 56.Fa value . 57.Sh RETURN VALUES 58Returns 59.Fa value 60round down to the previous power of\~2. 61If 62.Fa value 63is equal to zero, 64zero is returned. 65.Sh SEE ALSO 66.Xr stdbit 3 , 67.Xr stdc_bit_ceil 3 68.Sh STANDARDS 69The 70.Nm stdc_bit_floor_ Ns Em type Ns () 71family of functions and the 72.Fn stdc_bit_floor 73type-generic macro conform to 74.St -isoC-2023 . 75.Sh HISTORY 76The 77.Nm stdc_bit_floor_ Ns Em type Ns () 78family of functions and the 79.Fn stdc_bit_floor 80type-generic macro were added in 81.Fx 15.1. 82.Sh AUTHOR 83.An Robert Clausecker Aq Mt fuz@FreeBSD.org 84