vec_cx_mpy_12.c

dsp6713开发板的许多例程.对入门特别有用

void vec_cx_mpy(const short *restrict a, const short *restrict b,
                short *restrict c, int len, int shift)
{
    int i;
    unsigned a3_a2, a1_a0;             /* Packed 16-bit values        */
    unsigned b3_b2, b1_b0;             /* Packed 16-bit values        */
    short    a3, a2, a1, a0;           /* Separate 16-bit elements    */
    short    b3, b2, b1, b0;           /* Separate 16-bit elements    */
    short    c3, c2, c1, c0;           /* Separate 16-bit results     */
    unsigned c3_c2, c1_c0;             /* Packed 16-bit values        */

    for (i = 0; i < len; i += 4)
    {
        /* Load two complex numbers from the a[] array.               */
        /* The complex values loaded are represented as 'a3 + a2 * j' */
        /* and 'a1 + a0 * j'.  That is, the real components are a3    */
        /* and a1, and the imaginary components are a2 and a0.        */
        a3_a2 = _hi(*(const double *) &a[i]);
        a1_a0 = _lo(*(const double *) &a[i]);

        /* Load two complex numbers from the b[] array.               */
        b3_b2 = _hi(*(const double *) &b[i]);
        b1_b0 = _lo(*(const double *) &b[i]);

        /* Separate the 16-bit coefficients so that the complex       */
        /* multiply may be performed.  This portion needs further     */
        /* optimization.                                              */
        a3 = ((signed) a3_a2) >> 16;
        a2 = _ext(a3_a2, 16, 16);
        a1 = ((signed) a1_a0) >> 16;
        a0 = _ext(a1_a0, 16, 16);

        b3 = ((signed) a3_a2) >> 16;
        b2 = _ext(a3_a2, 16, 16);
        b1 = ((signed) a1_a0) >> 16;
        b0 = _ext(a1_a0, 16, 16);

        /* Perform the complex multiplies using 16x16 multiplies.     */
        c3 = (b3 * a2 + b2 * a3) >> 16;    
        c2 = (b3 * a3 - b2 * a2) >> 16;    

        c1 = (b1 * a0 + b0 * a1) >> 16;    
        c0 = (b1 * a1 - b0 * a0) >> 16;    

        /* Pack the 16-bit results into 32-bit words.                 */
        c3_c2 = _pack2(c3, c2);
        c1_c0 = _pack2(c1, c0);

        /* Store the results. */
        *(double *) &c[i] = _itod(c3_c2, c1_c0);
    }
}