* This function may be called from Pascal. It returns the distance
* between the stack and the heap as an unsigned 16-bit integer.
* IX contains the stack address, and the alternate HL pair contains
* the heap address. It appears to Pascal as:
* function space : integer;
* external;
entry space
space push ix
pop h HL = stack address
exx
push h
exx
pop d DE = heap address
dsbc d HL := distance between stack and heap
xchg DE := HL (function return in Pascal)
ret
