dot product using LDW

abdalla ali

Hello all

I'm about to write a code of floating point dot-product using software pipelining for TMS320C6713 by using LDW . I encountered a problem in the accumulation of the multiplication result ( I think it's loop carry path problem because the addsp require 4 cycles to complete ) . How can I solve this issue . I blevie that LDDW will be more effecitiant . I try it ...but how can i deal with odd number of multiplication( if count is an odd number ) ...one solution is done by add a zero coef at the end of the coefficient array but if i don't know the value of count if it even or odd

here the C code

float dot-product(float *in, float *coef, int count)
{
   int i;
   float sum = 0;

   for (i=0; i < count; i++)
   {
       sum = sum + in[i] * coef[i];
   }

   return(sum);
}

thank you ^_^

over 13 years ago

Alberto Chessa over 13 years ago

Mastermind 6670 points

Hi,

You can loop for (count & ~1) and then check if a trailing operation is required.

float dot_product(float *in, const float * const coef, int count)
{
    int i;
    float sum = 0;

    int c=count & ~1;
    _nassert(c % 2 == 0); //unroll by 2. Compiler generates LDDW
    _nassert((int)in % 8 == 0); //generate aligned access (LDDW instead of LDNDW)
    _nassert((int)coef % 8 == 0);
    for (i=0; i < c; i++)
    {
        sum = sum + in[i] * coef[i];
    }
    if (count & 1)
      sum+=in[count-1]*coef[count-1];
    return(sum);
}

You can try also with (count % 4 == 0) (unroll by 4), but of course you have to adjust the loop limits ant the trailing operations.

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dot product using LDW