snprintb(3)
- NetBSD Manual Pages
SNPRINTB(3) NetBSD Library Functions Manual SNPRINTB(3)
NAME
snprintb, snprintb_m -- bitmask output conversion
LIBRARY
System Utilities Library (libutil, -lutil)
SYNOPSIS
#include <util.h>
int
snprintb(char *buf, size_t bufsize, const char *fmt, uint64_t val);
int
snprintb_m(char *buf, size_t bufsize, const char *fmt, uint64_t val,
size_t max);
DESCRIPTION
The snprintb() function formats a bitmask into a mnemonic form suitable
for printing.
It formats the integer val into the buffer buf, of size bufsize, inter-
preting the bits within that integer as flags or groups of bits. 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 it would have written if the buffer were long
enough excluding the terminating NUL. If bufsize is zero, nothing is
written and buf may be a null pointer.
The snprintb_m() function accepts an additional max argument. If this
argument is zero, the snprintb_m() function behaves exactly like the
snprintb() function. If the max argument has a non-zero value, it repre-
sents 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).
The decoding directive in fmt describes how the bitfield is to be inter-
preted and displayed. It follows two possible formats, referred to as
``old'' and ``new''. The ``old'' format is limited to describing single
bits in a 32-bit value, the bit positions are 1-based. The ``new'' for-
mat supports multi-bit fields and 64-bit values, the bit positions are
0-based.
If the first character of fmt is (in C escape-character format) `\177' or
`\x7f', the remainder of the fmt argument follows the ``new'' format.
The next character (the first for the ``old'' format) specifies the
numeral base in which to print the numbers in the output. The possible
values are `\010' or `\x08' for octal, `\012' or `\x0a' for decimal, and
`\020' or `\x10' for hexadecimal.
The remaining characters in the fmt argument represent the formatting
conversions, according to the ``old'' or ``new'' format.
Old Format
In the ``old'' format, each conversion specifies a bit position and a
description that is printed if the corresponding bit is set.
The bit position is a 1-based single-byte binary value, ranging from
`\001' or `\x01' (1) for the least significant bit up to `\040' or `\x20'
(32) for the most significant bit.
The description is delimited by the next character whose value is 32 or
less (see ascii(7)), or by the end of the format string itself.
New Format
In the ``new'' format, each conversion begins with a conversion type,
followed by type-specific parameters, each encoded as a single byte, fol-
lowed by a NUL-terminated description. The bit positions are 0-based,
ranging from `\000' or `\x00' (0) for the least significant bit to `\077'
or `\x3f' (63) for the most significant bit.
b bit descr
Prints the description from descr if the bit at the position
bit is set.
f lsb width descr
Prints the description from descr, a delimiting `=' and the
numerical value of the multi-bit field whose least signifi-
cant bit is at lsb and that spans width bits. To print indi-
vidual values of the field, see the `=' and `*' conversions
below.
= cmp descr
Compares the field value from the previous `f' conversion to
the single-byte value cmp, ranging from `\000' or `\x00' (0)
to `\377' or `\xff' (255). If they are equal, prints `='
followed by the description from descr. This conversion may
be repeated.
F lsb width [descr]
Describes a multi-bit field like `f', but just extracts the
value for use with the `:' and `*' conversions below. The
description from descr is ignored, it is only present for
uniformity with the other conversions.
: cmp descr
Compares the field value from the previous `F' conversion to
the single-byte value cmp, ranging from `\000' or `\x00' (0)
to `\377' or `\xff' (255). If they are equal, prints the
description from descr. This conversion may be repeated.
* fmt If none of the previous `=' or `:' conversions matched,
prints the format string fmt via snprintf(3). The format
string fmt may contain a single uintmax_t conversion specifi-
cation to print the field value that did not match.
The new format is terminated by an additional NUL character at the end,
following that delimiting the last conversion. This NUL is supplied by
the compiler to terminate the string literal and doesn't need to be writ-
ten explicitly.
RETURN VALUES
The snprintb() and snprintb_m() functions return the number of bytes that
they 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, bufsize, "\010\002BITTWO\001BITONE", 3)
=> "03<BITTWO,BITONE>"
snprintb(buf, bufsize,
"\x10"
"\x10" "NOTBOOT"
"\x0f" "FPP"
"\x0e" "SDVMA"
"\x0c" "VIDEO"
"\x0b" "LORES"
"\x0a" "FPA"
"\x09" "DIAG"
"\x07" "CACHE"
"\x06" "IOCACHE"
"\x05" "LOOPBACK"
"\x04" "DBGCACHE",
0xe860)
=> "0xe860<NOTBOOT,FPP,SDVMA,VIDEO,CACHE,IOCACHE>"
An example of the new formatting style:
snprintb(buf, bufsize,
"\177\020"
"b\000" "LSB\0"
"b\001" "BITONE\0"
"f\004\004" "NIBBLE2\0"
"f\020\004" "BURST\0"
"=\x04" "FOUR\0"
"=\x0f" "FIFTEEN\0"
"b\037" "MSB\0",
0x800f0701)
=> "0x800f0701<LSB,NIBBLE2=0,BURST=0xf=FIFTEEN,MSB>"
The same example using snprintb_m:
snprintb_m(buf, bufsize,
"\177\020"
"b\000" "LSB\0"
"b\001" "BITONE\0"
"f\004\004" "NIBBLE2\0"
"f\020\004" "BURST\0"
"=\x04" "FOUR\0"
"=\x0f" "FIFTEEN\0"
"b\037" "MSB\0",
0x800f0701, 34)
=> "0x800f0701<LSB,NIBBLE2=0>\0"
"0x800f0701<BURST=0xf=FIFTEEN,MSB>\0"
""
A more complex example from <sys/mman.h> that uses both the single-bit
`b' formatting as well as the multi-bit field `F' formatting with a
default `*':
#define MAP_FMT "\177\020" \
"b\0" "SHARED\0" \
"b\1" "PRIVATE\0" \
"b\2" "COPY\0" \
"b\4" "FIXED\0" \
"b\5" "RENAME\0" \
"b\6" "NORESERVE\0" \
"b\7" "INHERIT\0" \
"b\11" "HASSEMAPHORE\0" \
"b\12" "TRYFIXED\0" \
"b\13" "WIRED\0" \
"F\14\1\0" \
":\0" "FILE\0" \
":\1" "ANONYMOUS\0" \
"b\15" "STACK\0" \
"F\30\010\0" \
":\000" "ALIGN=NONE\0" \
":\012" "ALIGN=1KB\0" \
":\013" "ALIGN=2KB\0" \
":\014" "ALIGN=4KB\0" \
":\015" "ALIGN=8KB\0" \
":\016" "ALIGN=16KB\0" \
":\017" "ALIGN=32KB\0" \
":\020" "ALIGN=64KB\0" \
":\021" "ALIGN=128KB\0" \
":\022" "ALIGN=256KB\0" \
":\023" "ALIGN=512KB\0" \
":\024" "ALIGN=1MB\0" \
":\025" "ALIGN=2MB\0" \
":\026" "ALIGN=4MB\0" \
":\027" "ALIGN=8MB\0" \
":\030" "ALIGN=16MB\0" \
":\034" "ALIGN=256MB\0" \
":\040" "ALIGN=4GB\0" \
":\044" "ALIGN=64GB\0" \
":\050" "ALIGN=1TB\0" \
":\054" "ALIGN=16TB\0" \
":\060" "ALIGN=256TB\0" \
":\064" "ALIGN=4PB\0" \
":\070" "ALIGN=64PB\0" \
":\074" "ALIGN=1EB\0" \
"*" "ALIGN=2^%ju\0"
snprintb(buf, bufsize, MAP_FMT, 0x0d001234)
=> "0xd001234<COPY,FIXED,RENAME,HASSEMAPHORE,ANONYMOUS,ALIGN=8KB>"
snprintb(buf, bufsize, MAP_FMT, 0x2e000000)
=> "0x2e000000<FILE,ALIGN=2^46>"
ERRORS
snprintb() will fail if:
[EINVAL] The leading character (for the ``old'' format) or the
second character (for the ``new'' format) does not
describe a supported numeral base, or a bit number in
the fmt argument is out of bounds, or the sequence of
conversions in the fmt argument is invalid, or
snprintf() failed.
SEE ALSO
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 earlier
releases. It was called bitmask_snprintf() in NetBSD 5.0 and earlier
releases.
AUTHORS
The ``new'' format was the invention of Chris Torek.
CAVEATS
When using hexadecimal character escapes for bit positions or field
widths, if a following description starts with one of the letters A to F,
that letter is considered part of the character escape. In such a situa-
tion, the character escape and the description must be put into separate
string literals, as in "\x0f" "FIFTEEN".
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