Added label initialization check to `vvi`.

[vvhitespace] / stdlib / README.md

# Overview #

This folder contains a library of useful functions written in VVhitespace.
Standard include guards are used with `cpp` to include the stdlib in user
programs. For an example, see `examples/hello-stdlib`.

# Reservations #

Since all labels share a global namespace, the standard library makes the
following reservations:

## Label ##

    00000000 0xxxxxxx - reserved for stdlib function entry points
    00000000 1xxxxxxx - unassigned
    0xxxxxxx xxxxxxxx - reserved for private use by stdlib
    1xxxxxxx xxxxxxxx - available for use in user programs

## Heap and Pointers ##

The first 16 heap addresses (`0-15`) are reserved when using the stdlib.

By convention, functions which return a pointer will use the address `0` to
represent a `NULL` pointer.

# Entry Points #

The following labels are entry points to stdlib functions. Read the
header comment for each function to learn the call and return stack.

         000xxx - reserved
         001xxx - print functions
           1000 ----- print string from stack       (stdio.pvvs)
           1001 ----- print string from heap        (stdio.pvvs)
           1010 ----- print number from stack       (stdio.pvvs)
         010xxx - math functions
          10000 ----- random                        (math.pvvs)
          10001 ----- absolute value                (math.pvvs)
         011xxx - heap functions
          11000 ----- memset                        (heap.pvvs)
          11001 ----- memcpy                        (heap.pvvs)
          11010 ----- memrand                       (heap.pvvs)
          11011 ----- memcmp                        (heap.pvvs)
          11100 ----- memsrch                       (heap.pvvs)
          11101 ----- <empty>
          11110 ----- slurp                         (heap.pvvs)
          11111 ----- spew                          (heap.pvvs)
         100xxx - unassigned
         101xxx - unassigned
         110xxx - conversion functions
         111xxx - debug functions
         111000 ----- dump heap                     (debug.pvvs)
        1xxxxxx - reserved for less common entry points
        1000000 ----- print sign of number          (stdio.pvvs)
        1000001 ----- print magnitude of number     (stdio.pvvs)

# Misc #

By convention, each public stdlib label will have 8 bits of
private label space associated with it, formed as follows:

    00001000 xxxxxxxx - for use by 1000
    00001001 xxxxxxxx - for use by 1001
    ...etc

# Slurp and Spew #

The stdlib uses heap[1] to heap[15] as registers.

The `slurp` and `spew` functions facilitate this by `spew`ing the stack onto
the heap's pseudo-registers or `slurp`ing the pseudo-registers back to the
stack.  The functions preserve order in complementary fashion.

The `spew` function uses `heap[0]` for storage.