rework std.math.big.Int

Now there are 3 types:
 * std.math.big.int.Const
   - the memory is immutable, only stores limbs and is_positive
   - all methods operating on constant data go here
 * std.math.big.int.Mutable
   - the memory is mutable, stores capacity in addition to limbs and
     is_positive
   - methods here have some Mutable parameters and some Const
     parameters. These methods expect callers to pre-calculate the
     amount of resources required, and asserts that the resources are
     available.
 * std.math.big.int.Managed
   - the memory is mutable and additionally stores an allocator.
   - methods here perform the resource calculations for the programmer.
   - this is the high level abstraction from before

Each of these 3 types can be converted to the other ones.

You can see the use case for this in the self-hosted compiler, where we
only store limbs, and construct the big ints as needed.

This gets rid of the hack where the allocator was optional and the
notion of "fixed" versions of the struct. Such things are now modeled
with the `big.int.Const` type.

0 files changed, 0 insertions, 0 deletions