NAME

humanize_number —

format a number into a human readable form

LIBRARY

System Utilities Library (libutil, -lutil)

SYNOPSIS

#include <libutil.h>

int
humanize_number(char *buf, size_t len, int64_t number, const char *suffix, int scale, int flags);

DESCRIPTION

The humanize_number() function formats the signed 64-bit quantity given in number into buf. A space and then suffix is appended to the end. The buffer pointed to by buf must be at least len bytes long.

If the formatted number (including suffix) would be too long to fit into buf, then divide number by 1024 until it will. In this case, prefix suffix with the appropriate designator. The 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 HN_DIVISOR_1000 and HN_IEC_PREFIXES flags.

The traditional (default) prefixes are:

Prefix	Description	Multiplier	Multiplier 1000x
`(note)`	kilo	1024	1000
`M`	mega	1048576	1000000
`G`	giga	1073741824	1000000000
`T`	tera	1099511627776	1000000000000
`P`	peta	1125899906842624	1000000000000000
`E`	exa	1152921504606846976	1000000000000000000

Note: An uppercase K indicates a power of two, a lowercase k a power of ten.

The IEE/IEC (and now also SI) power of two prefixes are:

Prefix	Description	Multiplier
`Ki`	kibi	1024
`Mi`	mebi	1048576
`Gi`	gibi	1073741824
`Ti`	tebi	1099511627776
`Pi`	pebi	1125899906842624
`Ei`	exbi	1152921504606846976

The len argument must be at least 4 plus the length of suffix, in order to ensure a useful result is generated into buf. To use a specific prefix, specify this as scale (multiplier = 1024 ^ scale; when HN_DIVISOR_1000 is specified, multiplier = 1000 ^ scale). This cannot be combined with any of the scale flags below.

The following flags may be passed in scale:

HN_AUTOSCALE: Format the buffer using the lowest multiplier possible.
HN_GETSCALE: Return the prefix index number (the number of times number must be divided to fit) instead of formatting it to the buffer.

The following flags may be passed in flags:

HN_DECIMAL: If the final result is less than 10, display it using one decimal place.
HN_NOSPACE: Do not put a space between number and the prefix.
HN_B: Use ‘B’ (bytes) as prefix if the original result does not have a prefix.
HN_DIVISOR_1000: Divide number with 1000 instead of 1024.
HN_IEC_PREFIXES: Use the IEE/IEC notion of prefixes (Ki, Mi, Gi...). This flag has no effect when HN_DIVISOR_1000 is also specified.

RETURN VALUES

Upon success, the humanize_number function returns the number of characters that would have been stored in buf (excluding the terminating NUL) if buf was large enough, or -1 upon failure. Even upon failure, the contents of buf may be modified. If HN_GETSCALE is specified, the prefix index number will be returned instead.

STANDARDS

The HN_DIVISOR_1000 and HN_IEC_PREFIXES flags conform to ISO/IEC Std 80000-13:2008 and IEEE Std 1541-2002.

HISTORY

The humanize_number() function first appeared in NetBSD 2.0 and then in FreeBSD 5.3. The HN_IEC_PREFIXES flag was introduced in FreeBSD 9.0.

CAVEATS

For numbers greater than 999 using buffer length of 4 and less can cause rounding errors. When using HN_IEC_PREFIXES the same error occurs for buffer length of 5 or less.