# MUX Header Definition

    /*
    **	(c) COPYRIGHT MIT 1995.
    **	Please first read the full copyright statement in the file COPYRIGH.
    */

Define the parts of a mux header as defined by the MUX draft specification. This is not finalized so be warned!

This module is does not contain a `.c` file. It is a part of the W3C Sample Code Library.

    #ifndef HTMUXHEADER_H
    #define HTMUXHEADER_H

## Byte Swapping

MUX is currently using little endian headers.

    #ifdef WORDS_BIGENDIAN
    #define HT_WORDSWAP(a) ( ((a) << 24) | \
    		         (((a) << 8) & 0x00ff0000) | \
    		         (((a) >> 8) & 0x0000ff00) | \
    	                 ((unsigned int)(a) >> 24) )
    #else
    #define HT_WORDSWAP(a) ((a))
    #endif

## The MUX Header

Simple, huh?

    typedef unsigned int  HTMuxHeader;

### Generic Header flags

    #define MUX_LONG_LENGTH	0x80000000
    #define MUX_CONTROL	0x40000000

### Data Header Flags

    #define MUX_FLAGS       0x3C000000
    #define MUX_SYN		0x20000000
    #define MUX_FIN		0x10000000
    #define MUX_RST		0x08000000
    #define MUX_PUSH 	0x04000000

### Control Header Opcodes

    #define MUX_OPCODES     0x3C000000
    #define MUX_STRING	0x00000000
    #define MUX_STACK	0x04000000
    #define MUX_FRAGMENT	0x08000000
    #define MUX_CREDIT	0x0C000000

### Length and Session ID

    #define MUX_SESSION	0x03FC0000
    #define MUX_LENGTH	0x0003FFFF

## Macros for Byte Shifting

    #define MUX_SET_SID(sid)	((sid) << 18)
    #define MUX_SET_LEN(len)	((len))
    #define MUX_SET_PID             MUX_SET_LEN
    #define MUX_SET_OPCODE(op)      ((op) << 26)

    #define MUX_GET_SID(sid)	(((sid) & MUX_SESSION) >> 18)
    #define MUX_GET_LEN(len)	((len) & MUX_LENGTH)
    #define MUX_GET_PID             MUX_GET_LEN
    #define MUX_GET_OPCODE(op)      ((op) & MUX_OPCODES >> 26)

## Header Alignment

You can force 8 byte alignment by defining this to 1. Normally, we decide pr MUX segment whether we have to use a long header or not.

    #define LONG_LENGTH	0			     /* 4 or 8 bytes header? */
    #define MUX_IS_LONG(hdr)     ((hdr) & MUX_LONG_LENGTH)

    #define MUX_ALIGN(len)       ((len) + ((4-(len)%4) % 4))
    #define MUX_LONG_ALIGN(len)  ((len) + ((8-(len)%8) % 8))

## Default Values

    #define DEFAULT_CREDIT          4096

    #endif