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 9F 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 SYNOPSIS 26.In sys/stdbit.h 27.Ft generic_value_type 28.Fo stdc_bit_floor 29.Fa "generic_value_type value" 30.Fc 31.Ft "unsigned char" 32.Fo stdc_bit_floor_uc 33.Fa "unsigned char value" 34.Fc 35.Ft "unsigned short" 36.Fo stdc_bit_floor_us 37.Fa "unsigned short value" 38.Fc 39.Ft "unsigned int" 40.Fo stdc_bit_floor_ui 41.Fa "unsigned int value" 42.Fc 43.Ft "unsigned long" 44.Fo stdc_bit_floor_ul 45.Fa "unsigned long value" 46.Fc 47.Ft "unsigned long long" 48.Fo stdc_bit_floor_ull 49.Fa "unsigned long long value" 50.Fc 51.Sh DESCRIPTION 52The 53.Fn stdc_bit_floor 54family of functions determine the largest power of 2 that is not greater 55than 56.Fa value . 57If 58.Fa value 59is 0, then the function returns 0. 60.Pp 61The 62.Fn stdc_bit_floor 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_floor 78family returns the largest power of 2 that is not greater than 79.Fa value . 80These functions cannot fail. 81.Sh INTERFACE STABILITY 82.Sy Committed 83.Sh SEE ALSO 84.Xr stdc_bit_floor 3C , 85.Xr stdc_bit_ceil 9F , 86.Xr stdc_bit_width 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