[Xen-devel] source code

[Linda <lindaj@xxxxxxxx>]

Hi all,

    The following functions should compute the union, intersection and 
difference of two bitmaps.
    Please review the code.  Thank you.

Sincerely,

Linda Jacobson

int libxl_bitmap_union(libxl_ctx *ctx, libxl_bitmap *union_bitmap, 
libxl_bitmap *bitmap1, libxl_bitmap *bitmap2)
{
    int size;
    int rc;

    GC_INIT(ctx);

// if bitmaps aren't the same size, union should be size of larger bit map
    size = (bitmap1->size > bitmap2->size) ? bitmap1->size : bitmap2->size;

    libxl_bitmap_init(union_bitmap);
    rc = libxl_bitmap_alloc(ctx, union_bitmap, size);
    if (rc)
    {
        // I'm following the coding standards here.  First goto I've 
written in decades.
        goto out;
    }

    for (int bit = 0; bit < (size * 8); bit++)
    {
        // libxl_bitmap_test returns 0 if past end of bitmap
        // if the bit is set in either bitmap, set it in their union
        if (libxl_bitmap_test(bitmap1, bit))
        {
            libxl_bitmap_set(union_bitmap, bit);
        }
        else if (libxl_bitmap_test(bitmap2, bit))
        {
            libxl_bitmap_set(union_bitmap, bit);
        }
    }

out:
    GC_FREE;
    return rc;
}

int libxl_bitmap_intersection (libxl_ctx *ctx, libxl_bitmap 
*union_bitmap, libxl_bitmap *bitmap1, libxl_bitmap *bitmap2)
{
    int size;
    int rc;

    GC_INIT(ctx);

// if bitmaps aren't the same size, intersection should be size of 
smaller bit map
    size = (bitmap1->size > bitmap2->size) ? bitmap2->size : bitmap1->size;

    libxl_bitmap_init(union_bitmap);
    rc = libxl_bitmap_alloc(ctx, union_bitmap, size);
    if (rc)
    {
        goto out;
    }

    for (int bit = 0; bit < (size * 8); bit++)
    {
        // libxl_bitmap_test returns 0 if past end of bitmap
        // if the bit is set in both bitmaps, set it in their intersection
        if (libxl_bitmap_test (bitmap1, bit) && libxl_bitmap_test 
(bitmap2, bit) )
        {
            libxl_bitmap_set (intersection_bitmap, bit);
        }
    }

out:
    GC_FREE;
    return rc;
}
int libxl_bitmap_difference(libxl_ctx *ctx, libxl_bitmap *union_bitmap, 
libxl_bitmap *bitmap1, libxl_bitmap *bitmap2)
{
    int size;
    int rc;

    GC_INIT(ctx);

// if bitmaps aren't the same size, difference should be size of larger 
bit map
    size = (bitmap1->size > bitmap2->size) ? bitmap1->size : bitmap2->size;

    libxl_bitmap_init(union_bitmap);
    rc = libxl_bitmap_alloc(ctx, union_bitmap, size);
    if (rc)
    {
        goto out;
    }

    for (int bit = 0; bit < (size * 8); bit++)
    {
        /* libxl_bitmap_test returns 0 if past end of bitmap
         if the bit is set in one bitmap and not the other, set it in 
their difference
        NOTE:  if one bit map is larger, this will result in all bits 
being set past the size of the smaller bitmap;  if this is not
        the desired behavior, please let me know
        */

        if (libxl_bitmap_test (bitmap1, bit) && (!libxl_bitmap_test 
(bitmap2, bit)) )
        {
            libxl_bitmap_set (difference_bitmap, bit);
        }
    }

out:
    GC_FREE;
    return rc;
}

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