[m-dev.] for review: use bitsets in quantification

[Simon Taylor]

Fergus wrote:
> OK, I'll give up on `..` for now, and go back to just wanting to be
> able to support a dense_bitset type.  For that type, I need `first'
> and `last' methods.  I guess it doesn't strictly *need* contiguous
> to_int values, though.

I think it's better to leave the `enum' class as it is for now,
rather than add stuff which may or may not be useful later.
We can add a `bounded_enum' class derived from `enum'
for the `enum_first' and `enum_last' methods.

Here's a relative diff dealing with Fergus' recent review comments.
I intend to commit this soon, unless anyone objects.

Simon.


--- enum.m	2000/11/10 05:33:07	1.2
+++ enum.m	2000/11/10 05:58:40
@@ -5,11 +5,15 @@
 %-----------------------------------------------------------------------------%
 % File: enum.m.
 % Author: stayl.
-% Stability: low.
+% Stability: very low.
 %
 % This module provides the typeclass `enum', which describes
 % types which can be converted to and from integers without loss
 % of information.
+%
+% The interface of this module is likely to change.
+% At the moment it is probably best to only use the `enum'
+% type class for types to be stored in `sparse_bitset's.
 %
 %-----------------------------------------------------------------------------%
 
--- int.m	2000/11/10 05:27:35	1.3
+++ int.m	2000/11/10 05:29:01
@@ -221,7 +221,11 @@
 
 	% Used by floor_to_multiple_of_bits_per_int, placed
 	% here to make sure they go in the `.opt' file.
-:- func int__div_bits_per_int(int) = int.
+
+	% int__quot_bits_per_int(X) = X // bits_per_int.		
+:- func int__quot_bits_per_int(int) = int.
+
+	% int__times_bits_per_int(X) = X * bits_per_int.		
 :- func int__times_bits_per_int(int) = int.
 
 %-----------------------------------------------------------------------------%
@@ -313,7 +317,7 @@
 
 :- pragma inline(floor_to_multiple_of_bits_per_int/1).
 floor_to_multiple_of_bits_per_int(X) = Floor :-
-	Trunc = div_bits_per_int(X),
+	Trunc = quot_bits_per_int(X),
 	Floor0 = times_bits_per_int(Trunc),
 	( Floor0 > X ->
 		Floor = Floor0 - bits_per_int
@@ -476,7 +480,7 @@
 	Bits = ML_BITS_PER_INT;
 ").
 
-:- pragma c_code(int__div_bits_per_int(Int::in) = (Div::out),
+:- pragma c_code(int__quot_bits_per_int(Int::in) = (Div::out),
 		[will_not_call_mercury, thread_safe], "
 	Div = Int / ML_BITS_PER_INT;
 ").
--- sparse_bitset.m	2000/11/10 06:00:01	1.4
+++ sparse_bitset.m	2000/11/10 06:01:09
@@ -433,8 +433,13 @@
 		bits_for_index(Index, Offset, Bits),
 		Set = [make_bitset_elem(Offset, Bits) | Set0]
 	; BitToSet = Index - Offset0, BitToSet < bits_per_int ->
-		Bits = set_bit(Data0 ^ bits, BitToSet),
-		Set = [make_bitset_elem(Offset0, Bits) | Rest]
+		Bits0 = Data0 ^ bits,
+		( get_bit(Bits0, BitToSet) \= 0 ->
+			Set = Set0
+		;
+			Bits = set_bit(Bits0, BitToSet),
+			Set = [make_bitset_elem(Offset0, Bits) | Rest]
+		)
 	;
 		Set = [Data0 | insert_2(Rest, Index)]
 	).
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