Author: andreas
Date: Tue May 31 20:23:12 2005
New Revision: 9896
Modified:
trunk/fundev/sources/lib/collection-extensions/subseq.dylan
Log:
job: minor
Slight improvement of the case where a subsequence end is beyond the end
of the underlying sequence, some formatting fixes.
Modified: trunk/fundev/sources/lib/collection-extensions/subseq.dylan
==============================================================================
--- trunk/fundev/sources/lib/collection-extensions/subseq.dylan (original)
+++ trunk/fundev/sources/lib/collection-extensions/subseq.dylan Tue May 31
20:23:12 2005
@@ -9,7 +9,7 @@
//======================================================================
//
// Copyright (c) 1994 Carnegie Mellon University
-// Copyright (c) 1998, 1999, 2000 Gwydion Dylan Maintainers
+// Copyright (c) 1998 - 2004 Gwydion Dylan Maintainers
// All rights reserved.
//
// Use and copying of this software and preparation of derivative
@@ -80,6 +80,24 @@
// accessed at least once.
//============================================================================
+// Notes while reviewing the code ( -- andreas, 20050531)
+//
+// * Start and end are insufficiently checked. It is quite easy to generate
+// a subsequence of negative size by subsequence(foo, start: 5, end: 3).
+// * Also, passing a negative start gives access to data outside the
+// subsequence the user is allowed to see.
+// * The semantics of omitting the sequence end isn't well-defined,
+// especially given stretchy source sequences.
+// * The good news: the above problems are not exploitable because everything
+// is bounds-checked twice.
+// * The bad news: the performance leaves to be desired because everything
+// is bounds-checked twice.
+// * Design decision: signal bounds error at subsequence creation time vs.
+// element access time. The latter is more dynamic, the former gives
+// better performance.
+// * Feature wish: Read-only subsequences.
+
+
define abstract class <subsequence> (<sequence>)
constant slot source :: <sequence>,
required-init-keyword: source: ;
@@ -120,8 +138,7 @@
#key start: first = 0,
end: last) => (result ::
<generic-subsequence>);
- let sz = size(seq);
- let subseq-last = if (last & last < sz) last else sz end if;
+ let subseq-last = if (last) last else max(first, seq.size) end if;
let (init, limit, next, done?,
key, elem, elem-setter, copy) = forward-iteration-protocol(seq);
let state = for (i from 0 below first,
@@ -206,8 +223,7 @@
define method subsequence(seq :: <vector>,
#key start: first = 0,
end: last) => (result :: <vector-subsequence>);
- let seq-size = size(seq);
- let subseq-last = if (last) min(last, seq-size) else seq-size end;
+ let subseq-last = if (last) last else max(first, seq.size) end if;
if (instance?(seq, <string>))
make(<vs-subsequence>, source: seq, start: first, end: subseq-last);
else
@@ -256,14 +272,14 @@
vs-fip-current-element-setter, vs-fip-copy-state);
end method forward-iteration-protocol;
-define method size(c :: <vector-subsequence>) => (result :: <integer>);
+define inline method size(c :: <vector-subsequence>) => (result :: <integer>);
c.end-index - c.start-index;
end method size;
define method aref(c :: <vector-subsequence>,
#rest rest) => (result :: <object>);
let index = rest[0];
- if ((index < 0) | (index >= c.end-index - c.start-index))
+ if ((index < 0) | (index >= c.size))
signal("index out of bounds");
else
aref(c.source, index + c.start-index);
@@ -273,7 +289,7 @@
define method aref-setter(value, c :: <vector-subsequence>,
#rest rest) => (result :: <object>);
let index = rest[0];
- if ((index < 0) | (index >= c.end-index - c.start-index))
+ if ((index < 0) | (index >= c.size))
signal("index out of bounds");
else
aref(c.source, index + c.start-index) := value;
@@ -288,22 +304,21 @@
define method element(seq :: <vector-subsequence>, key :: <integer>,
#key default = subseq-no-default) => elt :: <object>;
- let index = seq.start-index + key;
case
- key < 0 | index >= seq.end-index =>
+ key < 0 | index >= seq.size =>
if (default == subseq-no-default)
error("No such element in %=: %=", seq, key);
else
default
end if;
- otherwise => seq.source[index];
+ otherwise => seq.source[key + seq.start-index];
end case;
end method element;
define method element-setter(value, seq :: <vector-subsequence>,
key :: <integer>) => (result :: <object>);
case
- key < 0 | key >= seq.end-index - seq.start-index =>
+ key < 0 | key >= seq.size =>
error("No such element in %=: %=", seq, key);
otherwise => seq.source[key + seq.start-index] := value;
end case;
@@ -312,8 +327,7 @@
define method subsequence(seq :: <string>,
#key start: first = 0,
end: last) => (result :: <string-subsequence>);
- let seq-size = size(seq);
- let subseq-last = if (last) min(last, seq-size) else seq-size end;
+ let subseq-last = if (last) last else max(start, seq.size) end;
if (instance?(seq, <vector>))
make(<vs-subsequence>, source: seq, start: first, end: subseq-last);
--
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