omxsp_blockexp_s16.c

来自「The OpenMAX DL (Development Layer) APIs 」· C语言 代码 · 共 98 行

/**
 * 
 * File Name:  omxSP_BlockExp_S16.c
 * OpenMAX DL: v1.0.2
 * Revision:   10586
 * Date:       Wednesday, March 5, 2008
 * 
 * (c) Copyright 2007-2008 ARM Limited. All Rights Reserved.
 * 
 * 
 *
 * Description:
 * This file contains module block exponent computation
 *
 */

#include "omxtypes.h"
#include "armOMX.h"
#include "omxSP.h"

/**
 * Function:  omxSP_BlockExp_S16   (2.2.2.2.2)
 *
 * Description:
 * Block exponent calculation for 16-bit and 32-bit signals (count leading 
 * sign bits). These functions compute the number of extra sign bits of all 
 * values in the 16-bit and 32-bit input vector pSrc and return the minimum 
 * sign bit count. This is also the maximum shift value that could be used in 
 * scaling the block of data.  The functions BlockExp_S16 and 
 * BlockExp_S32 return the values 15 and 31, respectively, for input vectors in 
 * which all entries are equal to zero.  
 *
 * Note: These functions differ from other DL functions by not returning the 
 *       standard OMXError but the actual result. 
 *
 * Input Arguments:
 *   
 *   pSrc - pointer to the input vector 
 *   len - number of elements contained in the input and output 
 *         vectors (0 < len < 65536) 
 *
 * Output Arguments:
 *   
 *   none 
 *
 * Return Value:
 *    
 *    Maximum exponent that may be used in scaling 
 *
 */


OMX_S32 omxSP_BlockExp_S16(
                            const OMX_S16 *pSrc, 
                            int           len
                            )
{
    OMX_S16 Var,MaxVar;
    OMX_S32 MinSignBits;
    
    
    /* Compute the Leading zeros */
    
    MaxVar = 0;
    
    do
    {
        Var = *pSrc++;
            
        /* Invert the bits of a Negative number */
        
        if(Var < 0)
        {
            Var = ~Var;
        }
        
        /* Compute the Maximum */
        
        if(Var > MaxVar)
        {
            MaxVar = Var;
        }
        
       len--;
    
    }while(len != 0);


    for (MinSignBits=15; (MaxVar>>(15-MinSignBits))!=0 ; MinSignBits--);


    return MinSignBits;

}

/* End of File */