Representation of Data Structures in OCAML

1
Representation ofData Structuresin OCAML
2
Register
Heap
int value
1
Header
Register
Register
pointer
Block
...
Register
3
Encoding

• int value encodes
• integer
• nullary constructor
• conversion for int values
• shl(x,1) 1
• shr(x,1)
• no conversion for pointers neededblocks are word
  aligned ? lowest bit is 0
• loose 1 bit for int representation
• no loss in address space

4
Header
0
7
8
9
10
31
tag
size
color (GC)

• tag
• distinguish constructors of a type
• 0 lt tag lt 247 for tuples, arrays, constructor
  terms

5
Special Tags (gt 248)

• 248 objects
• 249, 250 functions (see below)
• gt 251 non-heap data (GC does not look inside)
• 251 unused
• 252 strings
• 253 floats
• 254 float arrays
• 255 finalization

6
(Recursive) Functions
250
size
f
PC
start offset
249
let rec f x ...and g x ...and h x y
...
g
PC
249
start offset
h
PC
otherglobals