Please, add BC4 encoding about ispctexturecompressor HOT 5 OPEN

inline void load_block_interleaved_alpha(float block[16], uniform rgba_surface* uniform src, int xx, uniform int yy)
{
    for (uniform int y = 0; y<4; y++)
    for (uniform int x = 0; x<4; x++)
    {
        uniform uint8* uniform src_ptr = &src->ptr[min((yy * 4 + y), src->height-1)*src->stride];
        uint8* rgb = src_ptr + min((xx * 4 + x), src->width-1);

        block[y*4+x] = (int)rgb[0];
    }
}

inline void CompressBlockBC4(uniform rgba_surface src[], int xx, uniform int yy, uniform uint8 dst[])
{
	float block[16];
    uint32 data[2];

	load_block_interleaved_alpha(block, src, xx, yy);
    CompressBlockBC3_alpha(block, data);

	store_data(dst, (src->width+3)&~3, xx, yy, data, 2);
}

export void CompressBlocksBC4_ispc(uniform rgba_surface src[], uniform uint8 dst[])
{	
	for (uniform int yy = 0; yy<(src->height+3)/4; yy++)
	foreach (xx = 0 ... (src->width+3)/4)
	{
		CompressBlockBC4(src, xx, yy, dst);
	}
}