dot_prod_09.c

dsp6713开发板的许多例程.对入门特别有用

int dot_prod(const short *restrict a, const short *restrict b,
             short *restrict c, int len)
{
    int i;
    int      sum = 0;                  /* 32-bit accumulation         */
    unsigned a3_a2, a1_a0;             /* Packed 16-bit values        */
    unsigned b3_b2, b1_b0;             /* Packed 16-bit values        */
    double   c3_c2_dbl, c1_c0_dbl;     /* 32-bit prod in 64-bit pairs */
    int      c3, c2, c1, c0;           /* Separate 32-bit products    */
    unsigned c3_c2, c1_c0;             /* Packed 16-bit values        */

    for (i = 0; i < len; i += 4)
    {
        a3_a2 = _hi(*(const double *) &a[i]);
        a1_a0 = _lo(*(const double *) &a[i]);

        b3_b2 = _hi(*(const double *) &b[i]);
        b1_b0 = _lo(*(const double *) &b[i]);

        /* Multiply elements together, producing four products */
        c3_c2_dbl = _mpy2(a3_a2, b3_b2);
        c1_c0_dbl = _mpy2(a1_a0, b1_b0);

        /* Add each of the four products to the accumulation. */
        sum += _hi(c3_c2_dbl);
        sum += _lo(c3_c2_dbl);
        sum += _hi(c1_c0_dbl);
        sum += _lo(c1_c0_dbl);
    }

    return sum;
}