Byte Order Macros

Byte Order Macros — a portable way to convert between different byte orders

Synopsis


#include <glib.h>

#define             G_LITTLE_ENDIAN
#define             G_BIG_ENDIAN
#define             G_PDP_ENDIAN

#define             g_htonl                             (val)
#define             g_htons                             (val)
#define             g_ntohl                             (val)
#define             g_ntohs                             (val)

#define             GINT_FROM_BE                        (val)
#define             GINT_FROM_LE                        (val)

#define             GUINT_FROM_BE                       (val)
#define             GUINT_FROM_LE                       (val)

#define             GLONG_FROM_BE                       (val)
#define             GLONG_FROM_LE                       (val)

#define             GULONG_FROM_BE                      (val)
#define             GULONG_FROM_LE                      (val)

#define             GINT16_FROM_BE                      (val)
#define             GINT16_FROM_LE                      (val)

#define             GUINT16_FROM_BE                     (val)
#define             GUINT16_FROM_LE                     (val)

#define             GINT32_FROM_BE                      (val)
#define             GINT32_FROM_LE                      (val)

#define             GUINT32_FROM_BE                     (val)
#define             GUINT32_FROM_LE                     (val)

#define             GINT64_FROM_BE                      (val)
#define             GINT64_FROM_LE                      (val)

#define             GUINT64_FROM_BE                     (val)
#define             GUINT64_FROM_LE                     (val)

#define             GUINT16_SWAP_BE_PDP                 (val)
#define             GUINT16_SWAP_LE_BE                  (val)
#define             GUINT16_SWAP_LE_PDP                 (val)

#define             GUINT32_SWAP_BE_PDP                 (val)
#define             GUINT32_SWAP_LE_BE                  (val)
#define             GUINT32_SWAP_LE_PDP                 (val)

#define             GUINT64_SWAP_LE_BE                  (val)

Description

These macros provide a portable way to determine the host byte order and to convert values between different byte orders.

The byte order is the order in which bytes are stored to create larger data types such as the gint and glong values. The host byte order is the byte order used on the current machine.

Some processors store the most significant bytes (i.e. the bytes that hold the largest part of the value) first. These are known as big-endian processors.

Other processors (notably the x86 family) store the most significant byte last. These are known as little-endian processors.

Finally, to complicate matters, some other processors store the bytes in a rather curious order known as PDP-endian. For a 4-byte word, the 3rd most significant byte is stored first, then the 4th, then the 1st and finally the 2nd.

Obviously there is a problem when these different processors communicate with each other, for example over networks or by using binary file formats. This is where these macros come in. They are typically used to convert values into a byte order which has been agreed on for use when communicating between different processors. The Internet uses what is known as 'network byte order' as the standard byte order (which is in fact the big-endian byte order).

Note that the byte order conversion macros may evaluate their arguments multiple times, thus you should not use them with arguments which have side-effects.

Details

G_LITTLE_ENDIAN

#define G_LITTLE_ENDIAN 1234

Specifies one of the possible types of byte order. See G_BYTE_ORDER.

G_BIG_ENDIAN

#define G_BIG_ENDIAN    4321

Specifies one of the possible types of byte order. See G_BYTE_ORDER.

G_PDP_ENDIAN

#define G_PDP_ENDIAN    3412		/* unused, need specific PDP check */

Specifies one of the possible types of byte order (currently unused). See G_BYTE_ORDER.

g_htonl()

#define             g_htonl(val)

Converts a 32-bit integer value from host to network byte order.

`val` :	a 32-bit integer value in host byte order.
Returns :	`val` converted to network byte order.

g_htons()

#define             g_htons(val)

Converts a 16-bit integer value from host to network byte order.

`val` :	a 16-bit integer value in host byte order.
Returns :	`val` converted to network byte order.

g_ntohl()

#define             g_ntohl(val)

Converts a 32-bit integer value from network to host byte order.

`val` :	a 32-bit integer value in network byte order.
Returns :	`val` converted to host byte order.

g_ntohs()

#define             g_ntohs(val)

Converts a 16-bit integer value from network to host byte order.

`val` :	a 16-bit integer value in network byte order.
Returns :	`val` converted to host byte order.

GINT_FROM_BE()

#define GINT_FROM_BE(val)	(GINT_TO_BE (val))

Converts a gint value from big-endian to host byte order.

`val` :	a gint value in big-endian byte order.
Returns :	`val` converted to host byte order.

GINT_FROM_LE()

#define GINT_FROM_LE(val)	(GINT_TO_LE (val))

Converts a gint value from little-endian to host byte order.

`val` :	a gint value in little-endian byte order.
Returns :	`val` converted to host byte order.

GUINT_FROM_BE()

#define GUINT_FROM_BE(val)	(GUINT_TO_BE (val))

Converts a guint value from big-endian to host byte order.

`val` :	a guint value in big-endian byte order.
Returns :	`val` converted to host byte order.

GUINT_FROM_LE()

#define GUINT_FROM_LE(val)	(GUINT_TO_LE (val))

Converts a guint value from little-endian to host byte order.

`val` :	a guint value in little-endian byte order.
Returns :	`val` converted to host byte order.

GLONG_FROM_BE()

#define GLONG_FROM_BE(val)	(GLONG_TO_BE (val))

Converts a glong value from big-endian to the host byte order.

`val` :	a glong value in big-endian byte order.
Returns :	`val` converted to host byte order.

GLONG_FROM_LE()

#define GLONG_FROM_LE(val)	(GLONG_TO_LE (val))

Converts a glong value from little-endian to host byte order.

`val` :	a glong value in little-endian byte order.
Returns :	`val` converted to host byte order.

GULONG_FROM_BE()

#define GULONG_FROM_BE(val)	(GULONG_TO_BE (val))

Converts a gulong value from big-endian to host byte order.

`val` :	a gulong value in big-endian byte order.
Returns :	`val` converted to host byte order.

GULONG_FROM_LE()

#define GULONG_FROM_LE(val)	(GULONG_TO_LE (val))

Converts a gulong value from little-endian to host byte order.

`val` :	a gulong value in little-endian byte order.
Returns :	`val` converted to host byte order.

GINT16_FROM_BE()

#define GINT16_FROM_BE(val)	(GINT16_TO_BE (val))

Converts a gint16 value from big-endian to host byte order.

`val` :	a gint16 value in big-endian byte order.
Returns :	`val` converted to host byte order.

GINT16_FROM_LE()

#define GINT16_FROM_LE(val)	(GINT16_TO_LE (val))

Converts a gint16 value from little-endian to host byte order.

`val` :	a gint16 value in little-endian byte order.
Returns :	`val` converted to host byte order.

GUINT16_FROM_BE()

#define GUINT16_FROM_BE(val)	(GUINT16_TO_BE (val))

Converts a guint16 value from big-endian to host byte order.

`val` :	a guint16 value in big-endian byte order.
Returns :	`val` converted to host byte order.

GUINT16_FROM_LE()

#define GUINT16_FROM_LE(val)	(GUINT16_TO_LE (val))

Converts a guint16 value from little-endian to host byte order.

`val` :	a guint16 value in little-endian byte order.
Returns :	`val` converted to host byte order.

GINT32_FROM_BE()

#define GINT32_FROM_BE(val)	(GINT32_TO_BE (val))

Converts a gint32 value from big-endian to host byte order.

`val` :	a gint32 value in big-endian byte order.
Returns :	`val` converted to host byte order.

GINT32_FROM_LE()

#define GINT32_FROM_LE(val)	(GINT32_TO_LE (val))

Converts a gint32 value from little-endian to host byte order.

`val` :	a gint32 value in little-endian byte order.
Returns :	`val` converted to host byte order.

GUINT32_FROM_BE()

#define GUINT32_FROM_BE(val)	(GUINT32_TO_BE (val))

Converts a guint32 value from big-endian to host byte order.

`val` :	a guint32 value in big-endian byte order.
Returns :	`val` converted to host byte order.

GUINT32_FROM_LE()

#define GUINT32_FROM_LE(val)	(GUINT32_TO_LE (val))

Converts a guint32 value from little-endian to host byte order.

`val` :	a guint32 value in little-endian byte order.
Returns :	`val` converted to host byte order.

GINT64_FROM_BE()

#define GINT64_FROM_BE(val)	(GINT64_TO_BE (val))

Converts a gint64 value from big-endian to host byte order.

`val` :	a gint64 value in big-endian byte order.
Returns :	`val` converted to host byte order.

GINT64_FROM_LE()

#define GINT64_FROM_LE(val)	(GINT64_TO_LE (val))

Converts a gint64 value from little-endian to host byte order.

`val` :	a gint64 value in little-endian byte order.
Returns :	`val` converted to host byte order.

GUINT64_FROM_BE()

#define GUINT64_FROM_BE(val)	(GUINT64_TO_BE (val))

Converts a guint64 value from big-endian to host byte order.

`val` :	a guint64 value in big-endian byte order.
Returns :	`val` converted to host byte order.

GUINT64_FROM_LE()

#define GUINT64_FROM_LE(val)	(GUINT64_TO_LE (val))

Converts a guint64 value from little-endian to host byte order.

`val` :	a guint64 value in little-endian byte order.
Returns :	`val` converted to host byte order.

GUINT16_SWAP_BE_PDP()

#define GUINT16_SWAP_BE_PDP(val)	(GUINT16_SWAP_LE_BE (val))

Converts a guint16 value between big-endian and pdp-endian byte order. The conversion is symmetric so it can be used both ways.

`val` :	a guint16 value in big-endian or pdp-endian byte order.
Returns :	`val` converted to the opposite byte order.

GUINT16_SWAP_LE_BE()

#define             GUINT16_SWAP_LE_BE(val)

Converts a guint16 value between little-endian and big-endian byte order. The conversion is symmetric so it can be used both ways.

`val` :	a guint16 value in little-endian or big-endian byte order.
Returns :	`val` converted to the opposite byte order.

GUINT16_SWAP_LE_PDP()

#define GUINT16_SWAP_LE_PDP(val)	((guint16) (val))

Converts a guint16 value between little-endian and pdp-endian byte order. The conversion is symmetric so it can be used both ways.

`val` :	a guint16 value in little-endian or pdp-endian byte order.
Returns :	`val` converted to the opposite byte order.

GUINT32_SWAP_BE_PDP()

#define             GUINT32_SWAP_BE_PDP(val)

Converts a guint32 value between big-endian and pdp-endian byte order. The conversion is symmetric so it can be used both ways.

`val` :	a guint32 value in big-endian or pdp-endian byte order.
Returns :	`val` converted to the opposite byte order.

GUINT32_SWAP_LE_BE()

#define             GUINT32_SWAP_LE_BE(val)

Converts a guint32 value between little-endian and big-endian byte order. The conversion is symmetric so it can be used both ways.

`val` :	a guint32 value in little-endian or big-endian byte order.
Returns :	`val` converted to the opposite byte order.

GUINT32_SWAP_LE_PDP()

#define             GUINT32_SWAP_LE_PDP(val)

Converts a guint32 value between little-endian and pdp-endian byte order. The conversion is symmetric so it can be used both ways.

`val` :	a guint32 value in little-endian or pdp-endian byte order.
Returns :	`val` converted to the opposite byte order.

GUINT64_SWAP_LE_BE()

#define             GUINT64_SWAP_LE_BE(val)

Converts a guint64 value between little-endian and big-endian byte order. The conversion is symmetric so it can be used both ways.

`val` :	a guint64 value in little-endian or big-endian byte order.
Returns :	`val` converted to the opposite byte order.

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