static void gmc_mmx(uint8_t *dst, uint8_t *src,
                    int stride, int h, int ox, int oy,
                    int dxx, int dxy, int dyx, int dyy,
                    int shift, int r, int width, int height)
{
    const int w    = 8;
    const int ix   = ox  >> (16 + shift);
    const int iy   = oy  >> (16 + shift);
    const int oxs  = ox  >> 4;
    const int oys  = oy  >> 4;
    const int dxxs = dxx >> 4;
    const int dxys = dxy >> 4;
    const int dyxs = dyx >> 4;
    const int dyys = dyy >> 4;
    const uint16_t r4[4]   = { r, r, r, r };
    const uint16_t dxy4[4] = { dxys, dxys, dxys, dxys };
    const uint16_t dyy4[4] = { dyys, dyys, dyys, dyys };
    const uint64_t shift2  = 2 * shift;
#define MAX_STRIDE 4096U
#define MAX_H 8U
    uint8_t edge_buf[(MAX_H + 1) * MAX_STRIDE];
    int x, y;

    const int dxw = (dxx - (1 << (16 + shift))) * (w - 1);
     const int dyh = (dyy - (1 << (16 + shift))) * (h - 1);
     const int dxh = dxy * (h - 1);
     const int dyw = dyx * (w - 1);
    int need_emu  =  (unsigned) ix >= width  - w || width < w ||
                     (unsigned) iy >= height - h || height< h
                     ;
 
     if ( // non-constant fullpel offset (3% of blocks)
         ((ox ^ (ox + dxw)) | (ox ^ (ox + dxh)) | (ox ^ (ox + dxw + dxh)) |
         (oy ^ (oy + dyw)) | (oy ^ (oy + dyh)) | (oy ^ (oy + dyw + dyh))) >> (16 + shift) ||
        (dxx | dxy | dyx | dyy) & 15 ||
        (need_emu && (h > MAX_H || stride > MAX_STRIDE))) {
        ff_gmc_c(dst, src, stride, h, ox, oy, dxx, dxy, dyx, dyy,
                 shift, r, width, height);
        return;
    }

    src += ix + iy * stride;
    if (need_emu) {
        ff_emulated_edge_mc_8(edge_buf, src, stride, stride, w + 1, h + 1, ix, iy, width, height);
        src = edge_buf;
    }

    __asm__ volatile (
        "movd         %0, %%mm6         \n\t"
        "pxor      %%mm7, %%mm7         \n\t"
        "punpcklwd %%mm6, %%mm6         \n\t"
        "punpcklwd %%mm6, %%mm6         \n\t"
        :: "r" (1 << shift));

    for (x = 0; x < w; x += 4) {
        uint16_t dx4[4] = { oxs - dxys + dxxs * (x + 0),
                            oxs - dxys + dxxs * (x + 1),
                            oxs - dxys + dxxs * (x + 2),
                            oxs - dxys + dxxs * (x + 3) };
        uint16_t dy4[4] = { oys - dyys + dyxs * (x + 0),
                            oys - dyys + dyxs * (x + 1),
                            oys - dyys + dyxs * (x + 2),
                            oys - dyys + dyxs * (x + 3) };

        for (y = 0; y < h; y++) {
            __asm__ volatile (
                "movq      %0, %%mm4    \n\t"
                "movq      %1, %%mm5    \n\t"
                "paddw     %2, %%mm4    \n\t"
                "paddw     %3, %%mm5    \n\t"
                "movq   %%mm4, %0       \n\t"
                "movq   %%mm5, %1       \n\t"
                "psrlw    $12, %%mm4    \n\t"
                "psrlw    $12, %%mm5    \n\t"
                : "+m" (*dx4), "+m" (*dy4)
                : "m" (*dxy4), "m" (*dyy4));

            __asm__ volatile (
                "movq      %%mm6, %%mm2 \n\t"
                "movq      %%mm6, %%mm1 \n\t"
                "psubw     %%mm4, %%mm2 \n\t"
                "psubw     %%mm5, %%mm1 \n\t"
                "movq      %%mm2, %%mm0 \n\t"
                "movq      %%mm4, %%mm3 \n\t"
                "pmullw    %%mm1, %%mm0 \n\t" // (s - dx) * (s - dy)
                "pmullw    %%mm5, %%mm3 \n\t" // dx * dy
                "pmullw    %%mm5, %%mm2 \n\t" // (s - dx) * dy
                "pmullw    %%mm4, %%mm1 \n\t" // dx * (s - dy)

                "movd         %4, %%mm5 \n\t"
                "movd         %3, %%mm4 \n\t"
                "punpcklbw %%mm7, %%mm5 \n\t"
                "punpcklbw %%mm7, %%mm4 \n\t"
                "pmullw    %%mm5, %%mm3 \n\t" // src[1, 1] * dx * dy
                "pmullw    %%mm4, %%mm2 \n\t" // src[0, 1] * (s - dx) * dy

                "movd         %2, %%mm5 \n\t"
                "movd         %1, %%mm4 \n\t"
                "punpcklbw %%mm7, %%mm5 \n\t"
                "punpcklbw %%mm7, %%mm4 \n\t"
                "pmullw    %%mm5, %%mm1 \n\t" // src[1, 0] * dx * (s - dy)
                "pmullw    %%mm4, %%mm0 \n\t" // src[0, 0] * (s - dx) * (s - dy)
                "paddw        %5, %%mm1 \n\t"
                "paddw     %%mm3, %%mm2 \n\t"
                "paddw     %%mm1, %%mm0 \n\t"
                "paddw     %%mm2, %%mm0 \n\t"

                "psrlw        %6, %%mm0 \n\t"
                "packuswb  %%mm0, %%mm0 \n\t"
                "movd      %%mm0, %0    \n\t"

                : "=m" (dst[x + y * stride])
                : "m" (src[0]), "m" (src[1]),
                  "m" (src[stride]), "m" (src[stride + 1]),
                  "m" (*r4), "m" (shift2));
            src += stride;
        }
        src += 4 - h * stride;
    }
}

The product reads data past the end, or before the beginning, of the intended buffer.