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_WIDTH 3C 16.Os 17.Sh NAME 18.Nm stdc_bit_width , 19.Nm stdc_bit_width_uc , 20.Nm stdc_bit_width_us , 21.Nm stdc_bit_width_ui , 22.Nm stdc_bit_width_ul , 23.Nm stdc_bit_width_ull 24.Nd determine minimum bit width 25.Sh LIBRARY 26.Lb libc 27.Sh SYNOPSIS 28.In stdbit.h 29.Ft "unsigned int" 30.Fo stdc_bit_width 31.Fa "generic_value_type value" 32.Fc 33.Ft "unsigned int" 34.Fo stdc_bit_width_uc 35.Fa "unsigned char value" 36.Fc 37.Ft "unsigned int" 38.Fo stdc_bit_width_us 39.Fa "unsigned short value" 40.Fc 41.Ft "unsigned int" 42.Fo stdc_bit_width_ui 43.Fa "unsigned int value" 44.Fc 45.Ft "unsigned int" 46.Fo stdc_bit_width_ul 47.Fa "unsigned long value" 48.Fc 49.Ft "unsigned int" 50.Fo stdc_bit_width_ull 51.Fa "unsigned long long value" 52.Fc 53.Sh DESCRIPTION 54The 55.Fn stdc_bit_width 56family of functions returns the minimum number of bits required to store 57.Fa value . 58This is calculated by taking the log base 2 of 59.Fa value 60and adding 1; however, if 61.Fa value 62is 0, then the function returns 0. 63The 64.Fn stdc_bit_width 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_width 73family returns the minimum number of bits required to hold 74.Fa value . 75These functions cannot fail. 76.Sh EXAMPLES 77.Sy Example 1 78Printing the minimum bit width. 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%x\en", 88 stdc_bit_width_uc(0x95), 89 stdc_bit_width_us(0xff6), 90 stdc_bit_width_ui(UINT32_MAX), 91 stdc_bit_width_ull(0)); 92 return (0); 93} 94.Ed 95.Pp 96When compiled and run, this produces: 97.Bd -literal -offset indent 98$ ./a.out 990x8 0xc 0x20 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_floor 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