bitfield.c

Radvision rtpRtcp协议栈 4.5.0.18 版本

/***********************************************************************
        Copyright (c) 2002 RADVISION Ltd.
************************************************************************
NOTICE:
This document contains information that is confidential and proprietary
to RADVISION Ltd.. No part of this document may be reproduced in any
form whatsoever without written prior approval by RADVISION Ltd..

RADVISION Ltd. reserve the right to revise this publication and make
changes without obligation to notify any person of such revisions or
changes.
***********************************************************************/


/****************************************************************************

  bitfield.c  --  Bit-field manipulation

  Abstract:      Misc. routines for bit field manipulation.

****************************************************************************/


#include "bitfield.h"


#ifdef __cplusplus
extern "C" {
#endif



/*===========================================================================
**  == bitfieldSet() ==                                                    **
**                                                                         **
**  Sets a sequence of bits in an integer to a specified value.            **
**                                                                         **
**  PARAMETERS:                                                            **
**      value      The integer value to work on.                           **
**                                                                         **
**      bitfield   The bit sequence to insert into the integer.            **
**                                                                         **
**      nStartBit  This value specifies the list-segnificant bit index     **
**                 for the bit sequence.  e.g. if nStartBit is set to 1,   **
**                 and nBits is set to 3, the bit sequence will occupy     **
**                 bits 1 through 4.                                       **
**                                                                         **
**      nBits      The number of bits in the bit sequence.                 **
**                                                                         **
**  RETURNS:                                                               **
**      The new integer value.                                             **
**                                                                         **
**=========================================================================*/

RvUint32 bitfieldSet(
    IN  RvUint32    value,
    IN  RvUint32    bitfield,
    IN  int         nStartBit,
    IN  int         nBits)
{
    int mask = (1 << nBits) - 1;

    return (value & ~(mask << nStartBit)) +
           ((bitfield & mask) << nStartBit);
}

/*===========================================================================
**  == bitfieldGet() ==                                                    **
**                                                                         **
**  Retreives the sequence of bits in an integer.                          **
**                                                                         **
**  PARAMETERS:                                                            **
**      value      The integer value to work on.                           **
**                                                                         **
**      nStartBit  This value specifies the list-segnificant bit index     **
**                 of the bit sequence.  e.g. if nStartBit is set to 1,    **
**                 and nBits is set to 3, the bit sequence in bits 1       **
**                 through 4 is used.                                      **
**                                                                         **
**      nBits      The number of bits in the bit sequence.                 **
**                                                                         **
**  RETURNS:                                                               **
**      Returns the bit sequence.  The sequence will occupy bits           **
**      0..(Bits-1).                                                       **
**                                                                         **
**=========================================================================*/

RvUint32 bitfieldGet(
    IN  RvUint32    value,
    IN  int         nStartBit,
    IN  int         nBits)
{
    int mask = (1 << nBits) - 1;

    return (value >> nStartBit) & mask;
}



#ifdef __cplusplus
}
#endif