SNPRINTB(3) BSD Library Functions Manual SNPRINTB(3)
NAME
snprintb -- bitmask output conversion
LIBRARY
System Utilities Library (libutil, -lutil)
SYNOPSIS
#include <util.h>
int
snprintb(char *buf, size_t buflen, const char *fmt, uint64_t val);
int
snprintb_m(char *buf, size_t buflen, const char *fmt, uint64_t val, size_t max);
DESCRIPTION
The snprintb() function formats a bitmask into a mnemonic form suitable for printing.
This conversion is useful for decoding bit fields in device registers. It formats the integer val into the buffer buf, of size buflen, using
a specified radix and an interpretation of the bits within that integer as though they were flags. The buffer is always NUL-terminated. If
the buffer buf is too small to hold the formatted output, snprintb() will fill as much as it can, and return the number of bytes that would
have written if the buffer was long enough excluding the terminating NUL.
The decoding directive string fmt describes how the bitfield is to be interpreted and displayed. It follows two possible syntaxes, referred
to as ``old'' and ``new''. The main advantage of the ``new'' formatting is that it is capable of handling multi-bit fields.
The first character of fmt may be 177, indicating that the remainder of the format string follows the ``new'' syntax. The second character
(the first for the old format) is a binary character representation of the output numeral base in which the bitfield will be printed before
it is decoded. Recognized radix values (in C escape-character format) are 10 (octal), 12 (decimal), and 20 (hexadecimal).
The remaining characters in fmt are interpreted as a list of bit-position-description pairs. From here the syntaxes diverge.
The ``old'' format syntax is series of bit-position-description pairs. Each begins with a binary character value that represents the posi-
tion of the bit being described. A bit position value of one describes the least significant bit. Whereas a position value of 32 (octal 40,
hexadecimal 20, the ASCII space character) describes the most significant bit.
The remaining characters in a bit-position-description 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 (distinguishable by its value being <= 32), or the end of the
decoding directive string itself.
For the ``new'' format syntax, a bit-position-description begins with a field type followed by a binary bit-position and possibly a field
length. The least significant bit is bit-position zero, unlike the ``old'' syntax where it is one.
bB Describes a bit position. The bit-position B indicates the corresponding bit, as in the ``old'' format.
fBL Describes a multi-bit field beginning at bit-position B and having a bit-length of L. The remaining characters are printed as a
description of the field followed by '=' and the value of the field. The value of the field is printed in the base specified as the
second character of the decoding directive string fmt.
FBL Describes a multi-bit field like 'f', but just extracts the value for use with the '=' and ':' formatting directives described below.
=V The field previously extracted by the last 'f' or 'F' operator is compared to the byte 'V' (for values 0 through 255). If they are
equal, '=' followed by the string following 'V' is printed. This and the ':' operator may be repeated to annotate multiple possible
values.
:V Operates like the '=' operator, but omits the leading '='.
Finally, each field is delimited by a NUL (' ') character. By convention, the format string has an additional NUL character at the end,
following that delimiting the last bit-position-description pair.
The snprintb_m() function accepts an additional max argument. If this argument is zero, the snprintb_m() function returns exactly the same
results in the buf as the snprintb() function. If the max argument is present and has a non-zero value, it represents the maximum length of
a formatted string. If the formatted string would require more than max characters, the snprintb_m() function returns multiple formatted
strings in the output buffer buf. Each string is NUL-terminated, and the last string is followed by an additional NUL character (or, if you
prefer, a zero-length string).
RETURN VALUES
The snprintb() and snprintb_m() functions return the number of bytes that would have written to the buffer if there was adequate space,
excluding the final terminating NUL, or -1 in case an error occurred. For snprintb_m(), the NUL characters terminating each individual
string are included in the total number of bytes.
EXAMPLES
Two examples of the old formatting style:
snprintb(buf, buflen, "102BITTWO1BITONE", 3)
=> "3<BITTWO,BITONE>"
snprintb(buf, buflen,
"20x10NOTBOOTx0fFPPx0eSDVMAx0cVIDEO"
"x0bLORESx0aFPAx09DIAGx07CACHE"
"x06IOCACHEx05LOOPBACKx04DBGCACHE",
0xe860)
=> "e860<NOTBOOT,FPP,SDVMA,VIDEO,CACHE,IOCACHE>"
An example of the new formatting style:
snprintb(buf, buflen,
"177 20b LSB b1_BITONE f44NIBBLE2 "
"fx104BURST =4FOUR =xfSIXTEEN "
"bx1fMSB ",
0x800f0701)
=> "800f0701<LSB,NIBBLE2=0,BURST=f=SIXTEEN,MSB>"
ERRORS
snprintb() will fail if:
[EINVAL] The leading character does not describe a supported format, or snprintf() failed.
SEE ALSO
printf(3), snprintf(3)
HISTORY
The snprintb() function was originally implemented as a non-standard %b format string for the kernel printf() function in NetBSD 1.5 and ear-
lier releases. It was called bitmask_snprintf() in NetBSD 5.0 and earlier releases.
AUTHORS
The ``new'' format was the invention of Chris Torek.
BSD
May 7, 2009 BSD