rgb24转yuv420p

#define SCALEBITS            8
#define ONE_HALF             (1 << (SCALEBITS - 1))
#define FIX(x)               ((int) ((x) * (1L<> SCALEBITS;
            r = p[3];
            g = p[4];
            b = p[5];
            r1 += r;
            g1 += g;
            b1 += b;
            lum[1] = (FIX(0.29900) * r + FIX(0.58700) * g +FIX(0.11400) * b + ONE_HALF) >> SCALEBITS;
            p += wrap3;
            lum += wrap;
            r = p[0];
            g = p[1];
            b = p[2];
            r1 += r;
            g1 += g;
            b1 += b;
            lum[0] = (FIX(0.29900) * r + FIX(0.58700) * g +FIX(0.11400) * b + ONE_HALF) >> SCALEBITS;
            r = p[3];
            g = p[4];
            b = p[5];
            r1 += r;
            g1 += g;
            b1 += b;
            lum[1] = (FIX(0.29900) * r + FIX(0.58700) * g +FIX(0.11400) * b + ONE_HALF) >> SCALEBITS;
   
            cb[0] = (((- FIX(0.16874) * r1 - FIX(0.33126) * g1 +
    FIX(0.50000) * b1 + 4 * ONE_HALF - 1) >> (SCALEBITS + 2)) + 128);
            cr[0] = (((FIX(0.50000) * r1 - FIX(0.41869) * g1 -
    FIX(0.08131) * b1 + 4 * ONE_HALF - 1) >> (SCALEBITS + 2)) + 128);
            cb++;
            cr++;
            p += -wrap3+2 * 3;
            lum += -wrap + 2;
        }
        p += wrap3;
        lum += wrap;
    }
}