255 lines
6.6 KiB
Groff
255 lines
6.6 KiB
Groff
.\" $OpenBSD: printf.9,v 1.26 2022/09/11 06:38:11 jmc Exp $
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.\" $NetBSD: kprintf.9,v 1.6 1999/03/16 00:40:47 garbled Exp $
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.\"
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.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jeremy Cooper.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd $Mdocdate: September 11 2022 $
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.Dt PRINTF 9
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.Os
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.Sh NAME
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.Nm printf ,
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.Nm snprintf ,
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.Nm vprintf ,
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.Nm vsnprintf ,
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.Nm uprintf ,
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.Nm ttyprintf ,
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.Nm db_printf ,
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.Nm db_vprintf
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.Nd kernel formatted output conversion
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/systm.h
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.Ft int
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.Fo printf
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.Fa "const char *format"
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.Fa "..."
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.Fc
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.Ft int
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.Fo snprintf
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.Fa "char *buf"
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.Fa "size_t size"
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.Fa "const char *format"
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.Fa "..."
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.Fc
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.Ft int
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.Fo vprintf
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.Fa "const char *format"
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.Fa "va_list ap"
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.Fc
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.Ft int
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.Fo vsnprintf
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.Fa "char *buf"
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.Fa "size_t size"
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.Fa "const char *fmt"
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.Fa "va_list ap"
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.Fc
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.Ft void
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.Fo uprintf
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.Fa "const char *format"
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.Fa "..."
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.Fc
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.Ft void
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.Fo ttyprintf
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.Fa "struct tty *tty"
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.Fa "const char *format"
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.Fa "..."
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.Fc
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.In ddb/db_output.h
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.Ft void
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.Fn db_printf "const char *format" ...
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.Ft void
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.Fn db_vprintf "const char *format" "va_list ap"
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.Sh DESCRIPTION
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The
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.Fn printf ,
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.Fn snprintf ,
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.Fn vprintf ,
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.Fn vsnprintf ,
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.Fn uprintf ,
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.Fn ttyprintf ,
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.Fn db_printf ,
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and
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.Fn db_vprintf
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functions allow the kernel to send formatted messages to various output
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devices.
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The functions
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.Fn printf
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and
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.Fn vprintf
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send formatted strings to the system console and to the system log.
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The functions
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.Fn uprintf
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and
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.Fn ttyprintf
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send formatted strings to the current process's controlling tty and a specific
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tty,
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respectively.
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The functions
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.Fn db_printf
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and
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.Fn db_vprintf
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send formatted strings to the ddb console, and are only used to implement
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.Xr ddb 4 .
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.Pp
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Since each of these kernel functions is a variant of its user space
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counterpart, this page describes only the differences between the user
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space and kernel versions.
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.Pp
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Only a subset of the user space conversion specification is available to the
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kernel version:
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.Bd -filled -offset indent
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.Sm off
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.Cm %
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.Op Ar width
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.Op Ar size
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.Ar conversion
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.Sm on
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.Ed
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.Pp
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Refer to
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.Xr printf 3
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for functional details.
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.Ss FORMAT OPTIONS
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The kernel functions don't support as many formatting specifiers as their
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user space counterparts.
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In addition to the floating point formatting specifiers,
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the following integer type specifiers are not supported:
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.Bl -tag -width 5n
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.It Li %hh
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Argument of
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.Vt char
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type.
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This format specifier is accepted by the kernel but will be handled as
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.Li %h .
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.It Li %j
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Argument of
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.Vt intmax_t
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or
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.Vt uintmax_t
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type.
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.It Li %t
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Argument of
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.Vt ptrdiff_t
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type.
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.El
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.Pp
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The kernel functions support some additional formatting specifiers:
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.Bl -tag -width 5n
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.It Li %b
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Bit field expansion.
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This format specifier is useful for decoding bit fields in device registers.
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It displays an integer using a specified radix
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.Pq base
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and an interpretation of
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the bits within that integer as though they were flags.
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It requires two arguments from the argument vector, the first argument being
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the bit field to be decoded
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(of type
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.Vt int ,
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unless a width modifier has been specified)
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and the second being a decoding directive string.
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.Pp
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The decoding directive string describes how the bitfield is to be interpreted
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and displayed.
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The first character of the string is a binary character representation of the
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output numeral base in which the bitfield will be printed before it is decoded.
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Recognized radix values
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.Pq "in C escape-character format"
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are
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.Li \e10
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.Pq octal ,
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.Li \e12
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.Pq decimal ,
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and
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.Li \e20
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.Pq hexadecimal .
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.Pp
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The remaining characters in the decoding directive string are interpreted as a
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list of bit-position\(endescription pairs.
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A bit-position\(endescription pair begins with a binary character value
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that represents the position of the bit being described.
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A bit position value of one describes the least significant bit.
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Whereas a position value of 32
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.Pq "octal 40, hexadecimal 20, the ASCII space character"
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describes the most significant bit.
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.Pp
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To deal with more than 32 bits, the characters 128
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.Pq "octal 200, hexadecimal 80"
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through 255
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.Pq "octal 377, hexadecimal FF"
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are used.
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The value 127 is subtracted from the character to determine the
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bit position (1 is least significant, and 128 is most significant).
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.Pp
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The remaining characters in a bit-position\(endescription pair are the
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characters to print should the bit being described be set.
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Description strings are delimited by the next bit position value character
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encountered
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.Po
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distinguishable by its value being \*(Le 32 or \*(Ge 128
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.Pc ,
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or the end of the decoding directive string itself.
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.El
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.Sh RETURN VALUES
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The
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.Fn printf
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and
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.Fn vprintf
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functions return the number of characters printed.
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.Pp
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The
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.Fn snprintf
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and
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.Fn vsnprintf
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functions return the number of characters that would have been put into
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the buffer
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.Fa buf
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if the
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.Fa size
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were unlimited.
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.Sh EXAMPLES
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Use of the
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.Li %b
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format specifier for decoding device registers.
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.Bd -literal -offset indent
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printf("reg=%b\en", 3, "\e10\e2BITTWO\e1BITONE")
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\(rA "reg=3<BITTWO,BITONE>"
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printf("enablereg=%b\en", 0xe860,
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"\e20\ex10NOTBOOT\ex0fFPP\ex0eSDVMA\ex0cVIDEO"
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"\ex0bLORES\ex0aFPA\ex09DIAG\ex07CACHE"
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"\ex06IOCACHE\ex05LOOPBACK\ex04DBGCACHE")
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\(rA "enablereg=e860<NOTBOOT,FPP,SDVMA,VIDEO,CACHE,IOCACHE>"
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.Ed
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.Sh CODE REFERENCES
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.Pa sys/kern/subr_prf.c
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.Sh SEE ALSO
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.Xr revoke 2 ,
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.Xr printf 3 ,
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.Xr ddb 4 ,
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.Xr log 9
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