bitmap.c

// Macros used in the bitset algorithms.
#define INDEX_FROM_BIT(a) (a/(8*4))
#define OFFSET_FROM_BIT(a) (a%(8*4))

// Static function to set a bit in the frames bitset
static void set_frame(uint32_t frame_addr)
{
    uint32_t frame = frame_addr/0x1000;
    uint32_t idx = INDEX_FROM_BIT(frame);
    uint32_t off = OFFSET_FROM_BIT(frame);
    frames[idx] |= (0x1 << off);
}

// Static function to clear a bit in the frames bitset
static void clear_frame(uint32_t frame_addr)
{
    uint32_t frame = frame_addr/0x1000;
    uint32_t idx = INDEX_FROM_BIT(frame);
    uint32_t off = OFFSET_FROM_BIT(frame);
    frames[idx] &= ~(0x1 << off);
}

// Static function to test if a bit is set.
static uint32_t test_frame(uint32_t frame_addr)
{
    uint32_t frame = frame_addr/0x1000;
    uint32_t idx = INDEX_FROM_BIT(frame);
    uint32_t off = OFFSET_FROM_BIT(frame);
    return (frames[idx] & (0x1 << off));
}

// Static function to find the first free frame.
static uint32_t first_free_frame()
{
    uint32_t i, j;
    for (i = 0; i < INDEX_FROM_BIT(total_frames); i++) // loop over every bitmask byte
    {
				//fb_write("\n");
				//fb_write_hex(frames[i]);
        if (frames[i] != 0xFFFFFFFF) // nothing free, exit early.
        {
            // at least one bit is free here.
            for (j = 0; j < 32; j++)
            {
                uint32_t toTest = 0x1 << j;
                if ( !(frames[i]&toTest) )
                {
									// return the index of the free frame
									// e.g. the nth frame out of 4096 frames (16mb) is free
									//fb_write("first free frame idx: ");
									//fb_write_dec(i*4*8+j);
									return i*4*8+j;
                }
            }
        }
    }
}