#define GTINC(A,B,X) if(A>B)X++

int
cb_index (real pn[])
{
    real  d, distm = BIG;
    int
        j,
        is=0,           /* best shape index */
        ig=0,           /* best gain index */
        idxg,           /* current gain index */
        ichan;          /* resulting combined index */
    real CBMEM *shape_ptr = (real CBMEM *) cb_shape;
    real *sher_ptr  = shape_energy;
    real pcor, b0, b1, b2;
    real *pb=pn;
    real g2, gsq;
    register real
        cgm0 REG(r0) = cb_gain_mid_0,
        cgm1 REG(r1) = cb_gain_mid_1,
        x REG(r2),
        cgm2  = cb_gain_mid_2,
        energy REG(r4), y REG(r5),
        cor REG(r8) = 0,
        t REG(r12);
    register int minus5 REG(m0) = -5;

 
    for (j=0; j<NCWD; j++) {
        cor=cor-cor;
        energy = *sher_ptr++;

        /* Compute correlation of filtered input and codeword shapes*/
        b0 = cgm0 * energy; x=*shape_ptr++; y=*pb++;
                    t=x*y;  x=*shape_ptr++; y=*pb++;
        cor+=t;     t=x*y;  x=*shape_ptr++; y=*pb++;
        cor+=t;     t=x*y;  x=*shape_ptr++; y=*pb++;
        cor+=t;     t=x*y;  x=*shape_ptr++; y=*pb++;
        cor+=t;     t=x*y;
        cor+=t;     b1 = cgm1 * energy;

        /* Determine the appropriate gain level */
        pb += minus5;
        b2 = cgm2 * energy;
        idxg=idxg-idxg;
        pcor = cor;
        if (cor < 0.0) {
            pcor = -cor;
            idxg += 4;
        }
        GTINC(pcor, b0, idxg);
        GTINC(pcor, b1, idxg);
        GTINC(pcor, b2, idxg);

        /* Compute the distortion */
        g2 = cb_gain2[idxg];
        gsq = cb_gain_sq[idxg];
        d = gsq * energy - g2 * cor;

        /* Find the index with the minimum distortion */
        if (d < distm) {
            ig = idxg;
            is = j;
            distm = d;
        }
    }
    ichan = (is  << 3) + ig;
    return ichan;
}