byteorder.3

ecos实时嵌入式操作系统

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.Dd June 4, 1993
.Dt BYTEORDER 3
.Os
.Sh NAME
.Nm htonl ,
.Nm htons ,
.Nm ntohl ,
.Nm ntohs ,
.Nm htobe32 ,
.Nm htobe16 ,
.Nm betoh32 ,
.Nm betoh16 ,
.Nm htole32 ,
.Nm htole16 ,
.Nm letoh32 ,
.Nm letoh16 ,
.Nm swap32 ,
.Nm swap16
.Nd convert values between different byte orderings
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <machine/endian.h>
.Ft u_int32_t
.Fn htonl "u_int32_t host32"
.Ft u_int16_t
.Fn htons "u_int16_t host16"
.Ft u_int32_t
.Fn ntohl "u_int32_t net32"
.Ft u_int16_t
.Fn ntohs "u_int16_t net16"
.Ft u_int32_t
.Fn htobe32 "u_int32_t host32"
.Ft u_int16_t
.Fn htobe16 "u_int16_t host16"
.Ft u_int32_t
.Fn betoh32 "u_int32_t big32"
.Ft u_int16_t
.Fn betoh16 "u_int16_t big16"
.Ft u_int32_t
.Fn htole32 "u_int32_t host32"
.Ft u_int16_t
.Fn htole16 "u_int16_t host16"
.Ft u_int32_t
.Fn letoh32 "u_int32_t little32"
.Ft u_int16_t
.Fn letoh16 "u_int16_t little16"
.Ft u_int32_t
.Fn swap32 "u_int32_t val32"
.Ft u_int16_t
.Fn swap16 "u_int16_t val16"
.Sh DESCRIPTION
These routines convert 16- and 32-bit quantities between different
byte orderings.
The
.Dq swap
functions reverse the byte ordering of
the given quantity, the others converts either from/to the native
byte order used by the host to/from either little- or big-endian (a.k.a
network) order.
.Pp
Apart from the swap functions, the names can be described by this form:
{src-order}to{dst-order}{size}.
Both {src-order} and {dst-order} can take the following forms:
.Pp
.Bl -tag -width "be " -offset indent -compact
.It h
Host order.
.It n
Network order (big-endian).
.It be
Big-endian (most significant byte first).
.It le
Little-endian (least significant byte first).
.El
.Pp
One of the specified orderings must be
.Sq h .
{size} will take these forms:
.Pp
.Bl -tag -width "32 " -offset indent -compact
.It l
Long (32-bit, used in conjunction with forms involving
.Sq n ) .
.It s
Short (16-bit, used in conjunction with forms involving
.Sq n ) .
.It 16
16-bit.
.It 32
32-bit.
.El
.Pp
The swap functions are of the form: swap{size}.
.Pp
Names involving
.Sq n
convert quantities between network
byte order and host byte order.
The last letter
.Pf ( Sq s
or
.Sq l )
is a mnemonic
for the traditional names for such quantities,
.Li short
and
.Li long ,
respectively.
Today, the C concept of
.Li short
and
.Li long
integers need not coincide with this traditional misunderstanding.
On machines which have a byte order which is the same as the network
order, routines are defined as null macros.
.Pp
The functions involving either
.Dq be ,
.Dq le ,
or
.Dq swap
use the numbers
16 and 32 for specifying the bitwidth of the quantities they operate on.
Currently all supported architectures are either big- or little-endian
so either the
.Dq be
or
.Dq le
variants are implemented as null macros.
.Pp
The routines mentioned above which have either {src-order} or {dst-order}
set to
.Sq n
are most often used in
conjunction with Internet addresses and ports as returned by
.Xr gethostbyname 3
and
.Xr getservent 3 .
.Sh SEE ALSO
.Xr gethostbyname 3 ,
.Xr getservent 3
.Sh HISTORY
The
.Nm byteorder
functions appeared in
.Bx 4.2 .
.Sh BUGS
On the vax, alpha, i386, and so far mips,
bytes are handled backwards from most everyone else in the world.
This is not expected to be fixed in the near future.