bitfield.c

基于h323协议的软phone

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


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

  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