[project @ 2001-07-23 10:47:16 by simonmar]

[project @ 2001-07-23 10:47:16 by simonmar]
Small changes to improve GC performance slightly:

  - store the generation *number* in the block descriptor rather
    than a pointer to the generation structure, since the most
    common operation is to pull out the generation number, and
    it's one less indirection this way.

  - cache the generation number in the step structure too, which
    avoids an extra indirection in several places.