NetBSD/lib/libutil/snprintb.3

.\"     $NetBSD: snprintb.3,v 1.6 2008/04/30 13:10:52 martin Exp $
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.Dd July 28, 2000
.Dt SNPRINTB 3
.Os
.Sh NAME
.Nm snprintb
.Nd bitmask output conversion
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In util.h
.Ft int
.Fn "snprintb" "char *buf" "size_t buflen" "const char *fmt" "uint64_t val"
.Sh DESCRIPTION
The
.Fn snprintb
function formats a bitmask into a mnemonic form suitable for printing.
.Pp
This conversion is useful for decoding bit fields in device registers.
It formats the integer
.Fa val
into the buffer
.Fa buf ,
of size
.Fa buflen ,
using a specified radix and an interpretation of
the bits within that integer as though they were flags.
.Pp
The decoding directive string
.Fa fmt
describes how the bitfield is to be interpreted and displayed.
The first character of
.Fa fmt
is a binary character representation of the
output numeral base in which the bitfield will be printed before it is decoded.
Recognized radix values
.Pq "in C escape-character format"
are
.Li \e10
.Pq octal ,
.Li \e12
.Pq decimal ,
and
.Li \e20
.Pq hexadecimal .
.Pp
The remaining characters in
.Fa fmt
are interpreted as a list of bit-position\(endescription pairs.
A bit-position\(endescription pair begins with a binary character value
that represents the position of the bit being described.
A bit position value of one describes the least significant bit.
Whereas a position value of 32
.Pq "octal 40, hexadecimal 20, the ASCII space character"
describes the most significant bit.
.Pp
The remaining characters in a bit-position\(endescription pair are the
characters to print should the bit being described be set.
Description strings are delimited by the next bit position value character
encountered
.Pq "distinguishable by its value being \*[Le] 32" ,
or the end of the decoding directive string itself.
.Sh RETURN VALUES
The
.Fn snprintb
function returns the number of characters that are required to format the
value
.Fa val
given the format string
.Fa fmt
excluding the terminating NUL.
The returned string in
.Fa buf
is always NUL-terminated.
.Sh EXAMPLES
Two examples of the old formatting style:
.Bd -literal -offset indent
snprintb(buf, buflen, "\e10\e2BITTWO\e1BITONE", 3)
\(rA "3\*[Lt]BITTWO,BITONE\*[Gt]"

snprintb(buf, buflen
       "\e20\ex10NOTBOOT\ex0fFPP\ex0eSDVMA\ex0cVIDEO"
       "\ex0bLORES\ex0aFPA\ex09DIAG\ex07CACHE"
       "\ex06IOCACHE\ex05LOOPBACK\ex04DBGCACHE",
       0xe860)
\(rA "0xe860\*[Lt]NOTBOOT,FPP,SDVMA,VIDEO,CACHE,IOCACHE\*[Gt]"
.Ed
.Sh ERRORS
If the buffer
.Fa buf
is too small to hold the formatted output,
.Fn snprintb
will still return the buffer, containing a truncated string.
.Sh SEE ALSO
.Xr snprintf 3
.Sh HISTORY
The
.Fn snprintb
function was originally implemented as a non-standard
.Li %b
format string for the kernel
.Fn printf
function in
.Nx 1.5
and earlier releases.
It got implemented as
.Fn bitmap_snprintf
for
.Nx 1.6
and this version was used to implement
.Fn snprintb .
.Sh BUGS
.Fn snprintb
supports a new extended form of formatting string, which is not yet
described here.