[Spice-devel] [PATCH 7/8] Store surfaces_used in a bit-array

[Yonit Halperin]

On 08/20/2010 09:54 PM, alexl at redhat.com wrote:
> From: Alexander Larsson<alexl at redhat.com>
>
> This is smaller than a byte array, and allows us to skip full
> blocks of 32 ids in one check.
> ---

Hi,
why not use a linked list, for free surfaces, in a static 
UINT32[n_surfaces] array? Any reason besides space, which is 4k?

>
>   static _inline void FreeSurface(PDev *pdev, UINT32 surface_id)
>   {
> -   pdev->Res.surfaces_used[surface_id] = 0;
> +    UINT32 i, bitmask;
> +
> +    i = surface_id / 32;
> +    bitmask = (~0x80000000)>>  (surface_id % 32);
> +
> +    pdev->Res.surfaces_used[i]&= bitmask;
>   }
shouldn't it be ~(0x80000000 << (surface_id % 32))?

>
>
>   static UINT32 GetFreeSurface(PDev *pdev)
>   {
> -    UINT32 x;
> -
> -    //not effective, fix me
> -    for (x = 1; x<  pdev->n_surfaces; ++x) {
> -        if (!pdev->Res.surfaces_used[x]) {
> -            pdev->Res.surfaces_used[x] = 1;
> -            return x;
> +    UINT32 start = 1;
> +    UINT32 bit;
> +    UINT32 i, end_i;
> +    UINT32 bitmask;
> +    UINT32 used_mask;
> +    UINT32 res = 0;
> +
> +    i = start / 32;
> +    end_i = (pdev->n_surfaces + 31) / 32;
> +    bit = start % 32;
> +    bitmask = (0x80000000)>>  (bit % 32);
> +
> +    while (i<  end_i) {
> +        used_mask = pdev->Res.surfaces_used[i];
> +        /* Avoid checks early if no unused */
> +        if (used_mask == 0xffffffff) {
shouldn't it be used_mask != 0xffffffff?