246 lines
6.8 KiB
Groff
246 lines
6.8 KiB
Groff
.\" $NetBSD: snprintb.3,v 1.12 2009/03/26 05:00:10 uebayasi 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 March 26, 2009
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.Dt SNPRINTB 3
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.Os
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.Sh NAME
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.Nm snprintb
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.Nd bitmask output conversion
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.Sh LIBRARY
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.Lb libutil
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.Sh SYNOPSIS
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.In util.h
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.Ft int
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.Fn "snprintb" "char *buf" "size_t buflen" "const char *fmt" "u_quad_t val"
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.Sh DESCRIPTION
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The
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.Fn snprintb
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function formats a bitmask into a mnemonic form suitable for printing.
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.Pp
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This conversion is useful for decoding bit fields in device registers.
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It formats the integer
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.Fa val
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into the buffer
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.Fa buf ,
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of size
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.Fa buflen ,
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using a specified radix and an interpretation of
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the bits within that integer as though they were flags.
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The buffer is always NUL-terminated.
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If the buffer
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.Fa buf
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is too small to hold the formatted output,
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.Fn snprintb
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will fill as much as it can, and return the number of bytes
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that would have written if the buffer was long enough excluding the
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terminating NUL.
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.Pp
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The decoding directive string
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.Fa fmt
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describes how the bitfield is to be interpreted and displayed.
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It follows two possible syntaxes, referred to as
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.Dq old
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and
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.Dq new .
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The main advantage of the
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.Dq new
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formatting is that it is capable of handling multi-bit fields.
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.Pp
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The first character of
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.Fa fmt
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may be
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.Li \e177 ,
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indicating that the remainder of the format string follows the
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.Dq new
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syntax.
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The second character
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.Pq the first for the old format
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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
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.Fa fmt
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are interpreted as a list of bit-position\(endescription pairs.
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From here the syntaxes diverge.
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.Pp
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The
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.Dq old
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format syntax is series of bit-position\(endescription pairs.
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Each begins with a binary character value that represents the position
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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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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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.Pq distinguishable by its value being \*[Le] 32 ,
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or the end of the decoding directive string itself.
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.Pp
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For the
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.Dq new
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format syntax, a bit-position\(endescription begins with a field type
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followed by a binary bit-position and possibly a field length.
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The least significant bit is bit-position zero, unlike the
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.Dq old
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syntax where it is one.
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.Bl -tag -width "xxxxx"
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.It Cm b\eB
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Describes a bit position.
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The bit-position
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.Fa B
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indicates the corresponding bit, as in the
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.Dq old
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format.
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.It Cm f\eB\eL
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Describes a multi-bit field beginning at bit-position
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.Fa B
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and having a bit-length of
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.Fa L .
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The remaining characters are printed as a description of the field
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followed by
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.Sq \&=
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and the value of the field.
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The value of the field is printed in the base specified as the second
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character of the decoding directive string
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.Ar fmt .
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.It Cm F\eB\eL
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Describes a multi-bit field like
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.Sq f ,
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but just extracts the value for use with the
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.Sq \&=
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and
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.Sq \&:
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formatting directives described below.
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.It Cm \&=\eV
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The field previously extracted by the last
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.Sq f
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or
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.Sq F
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operator is compared to the byte
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.Sq Cm V
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.Pq for values 0 through 255 .
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If they are equal,
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.Sq \&=
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followed by the string following
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.Sq Cm V
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is printed.
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This and the
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.Sq \&:
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operator may be repeated to annotate multiple possible values.
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.It Cm :\eV
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Operates like the
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.Sq \&=
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operator, but omits the leading
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.Sq \&= .
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.El
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.Pp
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Finally, each field is delimited by a NUL
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.Pq Sq \e0
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character.
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By convention, the format string has an additional NUL character at
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the end, following that delimiting the last bit-position\(endescription
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pair.
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.Sh RETURN VALUES
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The
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.Fn snprintb
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function returns the number of bytes that would have written to the buffer
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if there was adequate space, excluding the terminating NUL, or \-1 in case
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an error occurred.
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.Sh EXAMPLES
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Two examples of the old formatting style:
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.Bd -literal -offset indent
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snprintb(buf, buflen, "\e10\e2BITTWO\e1BITONE", 3)
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\(rA "3\*[Lt]BITTWO,BITONE\*[Gt]"
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snprintb(buf, buflen,
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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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0xe860)
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\(rA "e860\*[Lt]NOTBOOT,FPP,SDVMA,VIDEO,CACHE,IOCACHE\*[Gt]"
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.Ed
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.Pp
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An example of the new formatting style:
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.Bd -literal -offset indent
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snprintb(buf, buflen,
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"\e177\e020b\e0LSB\e0b\e1_BITONE\e0f\e4\e4NIBBLE2\e0"
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"f\ex10\e4BURST\e0=\e4FOUR\e0=\exfSIXTEEN\e0"
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"b\ex1fMSB\e0\e0",
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0x800f0701)
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\(rA "800f0701\*[Lt]LSB,NIBBLE2=0,BURST=f=SIXTEEN,MSB\*[Gt]"
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.Ed
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.Sh ERRORS
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.Fn snprintb
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The leading character does not describe a supported format,
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or
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.Fn snprintf
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failed.
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.El
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.Sh SEE ALSO
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.Xr printf 3 ,
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.Xr snprintf 3
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.Sh HISTORY
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The
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.Fn snprintb
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function was originally implemented as a non-standard
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.Li %b
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format string for the kernel
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.Fn printf
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function in
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.Nx 1.5
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and earlier releases.
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It was called
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.Fn bitmask_snprintf
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in
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.Nx 5.0
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and earlier releases.
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.Sh AUTHORS
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The
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.Dq new
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format was the invention of
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.An Chris Torek .
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