freebsd-skq/lib/libutil/humanize_number.3

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.Dd October 7, 2013
.Dt HUMANIZE_NUMBER 3
.Os
.Sh NAME
.Nm humanize_number
.Nd format a number into a human readable form
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In libutil.h
.Ft int
.Fo humanize_number
.Fa "char *buf" "size_t len" "int64_t number" "const char *suffix"
.Fa "int scale" "int flags"
.Fc
.Sh DESCRIPTION
The
.Fn humanize_number
function formats the signed 64-bit quantity given in
.Fa number
into
.Fa buf .
A space and then
.Fa suffix
is appended to the end.
The buffer pointed to by
.Fa buf
must be at least
.Fa len
bytes long.
.Pp
If the formatted number (including
.Fa suffix )
would be too long to fit into
.Fa buf ,
then divide
.Fa number
by 1024 until it will.
In this case, prefix
.Fa suffix
with the appropriate designator.
The
.Fn humanize_number
function follows the traditional computer science conventions by
default, rather than the IEE/IEC (and now also SI) power of two
convention or the power of ten notion.
This behaviour however can be altered by specifying the
.Dv HN_DIVISOR_1000
and
.Dv HN_IEC_PREFIXES
flags.
.Pp
The traditional
.Pq default
prefixes are:
.Bl -column "Prefix" "Description" "1000000000000000000" -offset indent
.It Sy "Prefix" Ta Sy "Description" Ta Sy "Multiplier" Ta Sy "Multiplier 1000x"
.It Li (note) Ta No kilo Ta 1024 Ta 1000
.It Li M Ta No mega Ta 1048576 Ta 1000000
.It Li G Ta No giga Ta 1073741824 Ta 1000000000
.It Li T Ta No tera Ta 1099511627776 Ta 1000000000000
.It Li P Ta No peta Ta 1125899906842624 Ta 1000000000000000
.It Li E Ta No exa Ta 1152921504606846976 Ta 1000000000000000000
.El
.Pp
Note:
An uppercase K indicates a power of two, a lowercase k a power of ten.
.Pp
The IEE/IEC (and now also SI) power of two prefixes are:
.Bl -column "Prefix" "Description" "1000000000000000000" -offset indent
.It Sy "Prefix" Ta Sy "Description" Ta Sy "Multiplier"
.It Li Ki Ta No kibi Ta 1024
.It Li Mi Ta No mebi Ta 1048576
.It Li Gi Ta No gibi Ta 1073741824
.It Li Ti Ta No tebi Ta 1099511627776
.It Li Pi Ta No pebi Ta 1125899906842624
.It Li Ei Ta No exbi Ta 1152921504606846976
.El
.Pp
The
.Fa len
argument must be at least 4 plus the length of
.Fa suffix ,
in order to ensure a useful result is generated into
.Fa buf .
To use a specific prefix, specify this as
.Fa scale
.Po multiplier = 1024 ^ scale;
when
.Dv HN_DIVISOR_1000
is specified,
multiplier = 1000 ^ scale
.Pc .
This cannot be combined with any of the
.Fa scale
flags below.
.Pp
The following flags may be passed in
.Fa scale :
.Bl -tag -width ".Dv HN_DIVISOR_1000" -offset indent
.It Dv HN_AUTOSCALE
Format the buffer using the lowest multiplier possible.
.It Dv HN_GETSCALE
Return the prefix index number (the number of times
.Fa number
must be divided to fit) instead of formatting it to the buffer.
.El
.Pp
The following flags may be passed in
.Fa flags :
.Bl -tag -width ".Dv HN_DIVISOR_1000" -offset indent
.It Dv HN_DECIMAL
If the final result is less than 10, display it using one decimal place.
.It Dv HN_NOSPACE
Do not put a space between
.Fa number
and the prefix.
.It Dv HN_B
Use
.Ql B
(bytes) as prefix if the original result does not have a prefix.
.It Dv HN_DIVISOR_1000
Divide
.Fa number
with 1000 instead of 1024.
.It Dv HN_IEC_PREFIXES
Use the IEE/IEC notion of prefixes (Ki, Mi, Gi...).
This flag has no effect when
.Dv HN_DIVISOR_1000
is also specified.
.El
.Sh RETURN VALUES
Upon success, the
.Nm
function returns the number of characters that would have been stored in
.Fa buf
(excluding the terminating
.Dv NUL )
if
.Fa buf
was large enough, or \-1 upon failure.
Even upon failure, the contents of
.Fa buf
may be modified.
If
.Dv HN_GETSCALE
is specified, the prefix index number will be returned instead.
.Sh SEE ALSO
.Xr expand_number 3
.Sh STANDARDS
The
.Dv HN_DIVISOR_1000
and
.Dv HN_IEC_PREFIXES
flags
conform to
.Tn ISO/IEC
Std\~80000-13:2008
and
.Tn IEEE
Std\~1541-2002.
.Sh HISTORY
The
.Fn humanize_number
function first appeared in
.Nx 2.0
and then in
.Fx 5.3 .
The
.Dv HN_IEC_PREFIXES
flag was introduced in
.Fx 9.0 .
.Sh CAVEATS
For numbers greater than 999 using buffer length of 4 and less can cause
rounding errors.
When using
.Dv HN_IEC_PREFIXES
the same error occurs for buffer length of 5 or less.