scale_v2_c.c

TI公司C6000系列DSP（DM642）模拟视频采集与回显源代码

/* ======================================================================== */
/*  NAME                                                                    */
/*      scale_v2 -- Vertical scaling down by 2                              */

/*                                                                          */
/*  USAGE                                                                   */
/*      This routine has the following C prototype:                         */
/*                                                                          */
/*          void scale_v2                                                   */
/*          (                                                               */
/*              unsigned char *restrict   inp,                              */
/*              int                       pixs,                             */
/*              int                       stride,                           */
/*              int                       lns,                              */
/*              unsigned char *restrict   outp                              */
/*          )                                                               */
/*                                                                          */
/*      The scale_v2 routine accepts an array "inp" of "lns" lines each     */
/*      of "pixs" pixels seperated by "stride" bytes, and produces an       */
/*      output array "outp" of "lns >> 1" and "pixs" pixels.                */ 
/*                                                                          */
/*  DESCRIPTION                                                             */
/*      The scale_v2 algorithm performs vertical scaling by a factor of     */
/*  "2" by averaging succesive lines as opposed to mere pixel dropping.     */
/*                                                                          */
/*  TECHNIQUES                                                              */
/*      None                                                                */
/*                                                                          */
/*  ASSUMPTIONS                                                             */
/*      'lns' must be a multiple of 2, and can be greater than or equal     */
/*  to 2. The input and output pointers are double word aligned. The        */
/*  number of pixels to process is a multiple of eight, and the number      */
/*  of lines to process are two.                                            */
/*                                                                          */
/*  NOTES                                                                   */
/*                                                                          */
/*  SOURCE                                                                  */
/*     None                                                                 */
/* ------------------------------------------------------------------------ */
/*            Copyright (c) 2001 Texas Instruments, Incorporated.           */
/*                           All Rights Reserved.                           */
/* ======================================================================== */

#pragma CODE_SECTION(scale_v2_cn,   ".text:ansi");

#include "scale_v2_c.h"


void scale_v2_cn
(
    unsigned char *restrict   inp, 
    int                       pixs, 
    int                       stride, 
    int                       lns, 
    unsigned char *restrict   outp
)
{
    int i, j;

    unsigned char pix0, pix1;
    unsigned char out_pix;

    /*--------------------------------------------------------------------*/
    /*  Infrom the compiler of any safe assumptions that can be made.     */
    /*  These include assuming that the input and output pointers are     */
    /*  double word aligned, and the number of pixels to be processed     */
    /*  is a multiple of eight. In addition the number of lines is a      */
    /*  multiple of 2.                                                    */
    /*--------------------------------------------------------------------*/ 

    #ifndef NOASSUME
    _nassert((int)(pixs)%8 == 0);
    _nassert((int)(inp)%8  == 0);
    _nassert((int)(outp)%8 == 0);
    _nassert(stride != pixs);
    _nassert(pixs >= 64);
    _nassert(lns >= 2);
    #endif

    /*--------------------------------------------------------------------*/
    /*  The output image has half the number of lines of the input image. */
    /*  Load in pixels that are stride elements away and average them     */
    /*  after rounding. At the end of processing any two lines increment  */
    /*  the input pointer to jump by 2 lines.                             */
    /*--------------------------------------------------------------------*/

    for ( j = 0; j < (lns >> 1); j++)
    {
        #ifndef NOASSUME
        #pragma UNROLL(2);
        #endif

        for ( i = 0; i < pixs; i++)
        {
            pix0 = inp[i];
            pix1 = inp[i + stride];
            out_pix = (pix0 + pix1 + 1) >> 1;
            *outp++ = out_pix;
        }
   
        inp  += (2 * stride);
   }
}       

/* ======================================================================== */
/*  End of file:  scale_v2_c.c                                              */
/* ------------------------------------------------------------------------ */
/*            Copyright (c) 2002 Texas Instruments, Incorporated.           */
/*                           All Rights Reserved.                           */
/* ======================================================================== */