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 9F 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 SYNOPSIS 26.In sys/stdbit.h 27.Ft "unsigned int" 28.Fo stdc_bit_width 29.Fa "generic_value_type value" 30.Fc 31.Ft "unsigned int" 32.Fo stdc_bit_width_uc 33.Fa "unsigned char value" 34.Fc 35.Ft "unsigned int" 36.Fo stdc_bit_width_us 37.Fa "unsigned short value" 38.Fc 39.Ft "unsigned int" 40.Fo stdc_bit_width_ui 41.Fa "unsigned int value" 42.Fc 43.Ft "unsigned int" 44.Fo stdc_bit_width_ul 45.Fa "unsigned long value" 46.Fc 47.Ft "unsigned int" 48.Fo stdc_bit_width_ull 49.Fa "unsigned long long value" 50.Fc 51.Sh DESCRIPTION 52The 53.Fn stdc_bit_width 54family of functions returns the minimum number of bits required to store 55.Fa value . 56This is calculated by taking the log base 2 of 57.Fa value 58and adding 1; however, if 59.Fa value 60is 0, then the function returns 0. 61The 62.Fn stdc_bit_width 63function is generic and will operate on all 8, 16, 32, and 64-bit 64unsigned integers; however, it is only available in C23. 65The other functions all operate on a specific integer type, but 66otherwise behave the same and are available regardless of the C language 67version. 68.Sh CONTEXT 69These functions may be called from 70.Sy user , 71.Sy kernel , 72or 73.Sy interrupt 74context. 75.Sh RETURN VALUES 76The functions in the 77.Fn stdc_bit_width 78family returns the minimum number of bits required to hold 79.Fa value . 80These functions cannot fail. 81.Sh INTERFACE STABILITY 82.Sy Committed 83.Sh SEE ALSO 84.Xr stdc_bit_width 3C , 85.Xr stdc_bit_ceil 9F , 86.Xr stdc_bit_floor 9F , 87.Xr stdc_count_ones 9F , 88.Xr stdc_count_zero 9F , 89.Xr stdc_first_leading_one 9F , 90.Xr stdc_first_leading_zero 9F , 91.Xr stdc_first_trailing_one 9F , 92.Xr stdc_first_trailing_zero 9F , 93.Xr stdc_has_single_bit 9F , 94.Xr stdc_leading_ones 9F , 95.Xr stdc_leading_zeros 9F , 96.Xr stdc_trailing_ones 9F , 97.Xr stdc_trailing_zeros 9F 98