1.\" 2.\" This file and its contents are supplied under the terms of the 3.\" Common Development and Distribution License ("CDDL"), version 1.0. 4.\" You may only use this file in accordance with the terms of version 5.\" 1.0 of the CDDL. 6.\" 7.\" A full copy of the text of the CDDL should have accompanied this 8.\" source. A copy of the CDDL is also available via the Internet at 9.\" http://www.illumos.org/license/CDDL. 10.\" 11.\" 12.\" Copyright 2024 Oxide Computer Company 13.\" 14.Dd October 27, 2024 15.Dt STDC_BIT_FLOOR 3C 16.Os 17.Sh NAME 18.Nm stdc_bit_floor , 19.Nm stdc_bit_floor_uc , 20.Nm stdc_bit_floor_us , 21.Nm stdc_bit_floor_ui , 22.Nm stdc_bit_floor_ul , 23.Nm stdc_bit_floor_ull 24.Nd find largest power of 2 smaller than value 25.Sh LIBRARY 26.Lb libc 27.Sh SYNOPSIS 28.In stdbit.h 29.Ft generic_value_type 30.Fo stdc_bit_floor 31.Fa "generic_value_type value" 32.Fc 33.Ft "unsigned char" 34.Fo stdc_bit_floor_uc 35.Fa "unsigned char value" 36.Fc 37.Ft "unsigned short" 38.Fo stdc_bit_floor_us 39.Fa "unsigned short value" 40.Fc 41.Ft "unsigned int" 42.Fo stdc_bit_floor_ui 43.Fa "unsigned int value" 44.Fc 45.Ft "unsigned long" 46.Fo stdc_bit_floor_ul 47.Fa "unsigned long value" 48.Fc 49.Ft "unsigned long long" 50.Fo stdc_bit_floor_ull 51.Fa "unsigned long long value" 52.Fc 53.Sh DESCRIPTION 54The 55.Fn stdc_bit_floor 56family of functions determine the largest power of 2 that is not greater 57than 58.Fa value . 59If 60.Fa value 61is 0, then the function returns 0. 62.Pp 63The 64.Fn stdc_bit_floor 65function is generic and will operate on all 8, 16, 32, and 64-bit 66unsigned integers; however, it is only available in C23. 67The other functions all operate on a specific integer type, but 68otherwise behave the same and are available regardless of the C language 69version. 70.Sh RETURN VALUES 71The functions in the 72.Fn stdc_bit_floor 73family returns the largest power of 2 that is not greater than 74.Fa value . 75These functions cannot fail. 76.Sh EXAMPLES 77.Sy Example 1 78Printing the bit floor of an integer. 79.Bd -literal 80#include <stdbit.h> 81#include <stdio.h> 82#include <limits.h> 83 84int 85main(void) 86{ 87 printf("0x%x 0x%x 0x%x 0x%llx\en", 88 stdc_bit_floor_uc(0x2b), 89 stdc_bit_floor_us(0x1000), 90 stdc_bit_floor_ui(UINT32_MAX), 91 stdc_bit_floor_ull(0)); 92 return (0); 93} 94.Ed 95.Pp 96When compiled and run, this produces: 97.Bd -literal -offset indent 98$ ./a.out 990x20 0x1000 0x80000000 0x0 100.Ed 101.Sh INTERFACE STABILITY 102.Sy Committed 103.Sh MT-LEVEL 104.Sy Async-Signal-Safe 105.Sh SEE ALSO 106.Xr stdc_bit_ceil 3C , 107.Xr stdc_bit_width 3C , 108.Xr stdc_count_ones 3C , 109.Xr stdc_count_zero 3C , 110.Xr stdc_first_leading_one 3C , 111.Xr stdc_first_leading_zero 3C , 112.Xr stdc_first_trailing_one 3C , 113.Xr stdc_first_trailing_zero 3C , 114.Xr stdc_has_single_bit 3C , 115.Xr stdc_leading_ones 3C , 116.Xr stdc_leading_zeros 3C , 117.Xr stdc_trailing_ones 3C , 118.Xr stdc_trailing_zeros 3C , 119.Xr stdbit.h 3HEAD 120