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_COUNT_ONES 3C 16.Os 17.Sh NAME 18.Nm stdc_count_ones , 19.Nm stdc_count_ones_uc , 20.Nm stdc_count_ones_us , 21.Nm stdc_count_ones_ui , 22.Nm stdc_count_ones_ul , 23.Nm stdc_count_ones_ull 24.Nd count one bits 25.Sh LIBRARY 26.Lb libc 27.Sh SYNOPSIS 28.In stdbit.h 29.Ft "unsigned int" 30.Fo stdc_count_ones 31.Fa "generic_value_type value" 32.Fc 33.Ft "unsigned int" 34.Fo stdc_count_ones_uc 35.Fa "unsigned char value" 36.Fc 37.Ft "unsigned int" 38.Fo stdc_count_ones_us 39.Fa "unsigned short value" 40.Fc 41.Ft "unsigned int" 42.Fo stdc_count_ones_ui 43.Fa "unsigned int value" 44.Fc 45.Ft "unsigned int" 46.Fo stdc_count_ones_ul 47.Fa "unsigned long value" 48.Fc 49.Ft "unsigned int" 50.Fo stdc_count_ones_ull 51.Fa "unsigned long long value" 52.Fc 53.Sh DESCRIPTION 54The 55.Fn stdc_count_ones 56family of functions returns the number of one bits present in 57.Fa value . 58These functions are sometimes referred to as a population count. 59.Pp 60The 61.Fn stdc_count_ones 62function is generic and will operate on all 8, 16, 32, and 64-bit 63unsigned integers; however, it is only available in C23. 64The other functions all operate on a specific integer type, but 65otherwise behave the same and are available regardless of the C language 66version. 67.Sh RETURN VALUES 68The functions in the 69.Fn stdc_count_ones 70family always return the number of one bits in 71.Fa value . 72These functions cannot fail. 73.Sh EXAMPLES 74.Sy Example 1 75Printing the total number of one bits. 76.Bd -literal 77#include <stdbit.h> 78#include <stdio.h> 79#include <limits.h> 80 81int 82main(void) 83{ 84 printf("0x%x 0x%x 0x%x 0x%x\en", 85 stdc_count_ones_uc(0x42), 86 stdc_count_ones_us(0xa22b), 87 stdc_count_ones_ui(UINT32_MAX), 88 stdc_count_ones_ull(0)); 89 return (0); 90} 91.Ed 92.Pp 93When compiled and run, this produces: 94.Bd -literal -offset indent 95$ ./a.out 960x2 0x7 0x20 0x0 97.Ed 98.Sh INTERFACE STABILITY 99.Sy Committed 100.Sh MT-LEVEL 101.Sy Async-Signal-Safe 102.Sh SEE ALSO 103.Xr stdc_bit_ceil 3C , 104.Xr stdc_bit_floor 3C , 105.Xr stdc_bit_width 3C , 106.Xr stdc_count_zeros 3C , 107.Xr stdc_first_leading_one 3C , 108.Xr stdc_first_leading_zero 3C , 109.Xr stdc_first_trailing_one 3C , 110.Xr stdc_first_trailing_zero 3C , 111.Xr stdc_has_single_bit 3C , 112.Xr stdc_leading_ones 3C , 113.Xr stdc_leading_zeros 3C , 114.Xr stdc_trailing_ones 3C , 115.Xr stdc_trailing_zeros 3C , 116.Xr stdbit.h 3HEAD 117