The updated spec follows. The requested binding is patch.
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Standard C Library Functions strfnum(3C)
NAME
strfnum, strfunum - format a number as a scaled string
SYNOPSIS
#include <string.h>
int strfnum(char *restrict buffer, size_t buf_len,
const char *restrict fmt, intmax_t value);
int strfunum(char *restrict buffer, size_t buf_len,
const char *restrict fmt, uintmax_t value);
DESCRIPTION
The strfnum(), strfunum() functions will convert the integer
<value> to a string, which will write at most <buf_len> bytes
to the output <buffer>. The format of the output string is
described by the <fmt> string.
Conversion Specification
The <fmt> string determines how <value> will be formatted to
the output in a fashion similar to sprintf(). Each conversion
specifier within the string consists of the % character, after
which the following appear in sequence:
o Zero or more of the following modifiers:
'0' : the resulting string is zero padded.
'-' : the resulting string is left aligned.
'+' : the resulting string's first char is a
'+' if result is greater than zero.
' ' : the resulting string's first char is a
space is the result is greater than zero;
used only if the '+' modifier is not
defined.
'#' : suppress trailing zeroes.
't' : include thousands separator(s).
'u' : suppress unit suffix.
o An optional decimal length. If the result is smaller,
the output will be padded according to the modifiers
if present, otherwise the result will be space-padded.
o An optional decimal precision, expressed as .# where
# is an unsigned decimal integer. When not specified,
three digits is the default precision.
o An optional 'b' character, which will express the result
as radix-2 rather than radix-10 (radix 2 uses 1024^N
whereas the default of radix 10 uses 1000^N to convert
the number).
o One character from the following set:
'A' : the unit is choosen automatically for the best
human-readable result. The integer part of the
result will be between 0 and 999 when radix-10
is used for the conversion, or 0 to 1023 when
radix-2 is used for the conversion.
'N' : use no units for conversion (will divide by 1).
'K' : use the SI unit of kilo.
'M' : use the SI unit of mega.
'G' : use the SI unit of giga.
'P' : use the SI unit of peta.
'T' : use the SI unit of tera.
'E' : use the SI unit of exa.
'%' : output a literal % character.
RETURN VALUE
The strfnum() function returns the number of bytes
written into <buffer> if less than or equal to <buf_len>,
otherwise returns the number of bytes that would have been
written to <buffer> if <buf_len> had been sufficiently large.
The value of <buf_len> may be passed as zero, and/or <buffer>
may be a null pointer; this will result in a return value of
the minimal-length buffer required to contain a complete
result (minus a terminating NUL character).
EXAMPLES
strfnum(buffer, len, "%5M", 123456789)
will output "123.457M" into the buffer
strfnum(buffer, len, "%5.M", 123456789)
will output " 123M" into the buffer
strfnum(buffer, len, "%5.0M", 123456789)
will output " 123M" into the buffer
strfnum(buffer, len, "%5.1M", 123456789)
will output "123.5M" into the buffer
strfnum(buffer, len, "%5.2M", 123456789)
will output "123.46M" into the buffer
strfnum(buffer, len, "%5.3M", 123456789)
will output "123.457M" into the buffer
strfnum(buffer, len, "%5.4M", 123456789)
will output "123.4568M" into the buffer
strfnum(buffer, len, "%+5.2K", 123456789)
will output "+123456.79K" into the buffer
strfnum(buffer, len, "%N", 123456789)
will output "123456789" into the buffer.
strfnum(buffer, len, "%A", 0)
will output "0.000" into the buffer.
strfnum(buffer, len, "%b", 0)
will output "0.000" into the buffer.
strfnum(buffer, len, "%bK", 0)
will output "0.000K" into the buffer.
strfnum(buffer, len, "%ubK", 1024)
will output "1.000" into the buffer.
strfnum(buffer, len, "FOO %0#5.4bA BAR", 1047552);
will output "FOO 01023K BAR" into the buffer.
NOTES
The radix and thousands characters follow the
current locale setting.
ATTRIBUTES
Interface Stability Committed
MT-Level Thread and async-signal safe
