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Fixed: Investigate performance of lastIndexOf #614 #1076

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Merged
merged 2 commits into from
Jul 6, 2017
+24 −6
Merged

Fixed: Investigate performance of lastIndexOf #614 #1076

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f5f122e
Added lower bound in lastIndexOf
jasigal Jun 29, 2017
bb31bb5
Added regression test for lastIndexOf
jasigal Jun 29, 2017
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7 changes: 7 additions & 0 deletions regression/strings-smoke-tests/java_last_index_of2/test.desc
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
CORE
test_last_index_of2.class
--refine-strings
^EXIT=0$
^SIGNAL=0$
^VERIFICATION SUCCESSFUL$
--
Binary file added regression/strings-smoke-tests/java_last_index_of2/test_last_index_of2.class
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8 changes: 8 additions & 0 deletions regression/strings-smoke-tests/java_last_index_of2/test_last_index_of2.java
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@@ -0,0 +1,8 @@
public class test_last_index_of2
{
public static void main(String[] args)
{
String letters = "automatictestcasegenerationatdiffblue";
assert(letters.lastIndexOf("diffblue", 25)==-1);
}
}
15 changes: 9 additions & 6 deletions src/solvers/refinement/string_constraint_generator_indexof.cpp
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Expand Up @@ -193,20 +193,22 @@ exprt string_constraint_generatort::add_axioms_for_last_index_of_string(
symbol_exprt contains=fresh_boolean("contains_substring");

// We add axioms:
// a1 : contains ==> offset <= from_index && offset <= |haystack| - |needle|
// a1 : contains ==> -1 <= offset && offset <= from_index
// && offset <= |haystack| - |needle|
// a2 : !contains <=> offset = -1
// a3 : forall n:[0, needle.length[,
// a3 : forall n:[0, |needle|[,
// contains ==> haystack[n+offset] = needle[n]
// a4 : forall n:[offset+1, min(from_index, |haystack| - |needle|)].
// contains ==>
// (exists m:[0,|substring|[. haystack[m+n] != needle[m]])
// (exists m:[0,|needle|[. haystack[m+n] != needle[m]])
// a5: forall n:[0, min(from_index, |haystack| - |needle|)].
// !contains ==>
// (exists m:[0,|substring|[. haystack[m+n] != needle[m])
// (exists m:[0,|needle|[. haystack[m+n] != needle[m])

implies_exprt a1(
contains,
and_exprt(
binary_relation_exprt(from_integer(-1, index_type), ID_le, offset),
binary_relation_exprt(
offset, ID_le, minus_exprt(haystack.length(), needle.length())),
binary_relation_exprt(offset, ID_le, from_index)));
Expand Down Expand Up @@ -255,8 +257,8 @@ exprt string_constraint_generatort::add_axioms_for_last_index_of_string(
{
// Unfold the existential quantifier as a disjunction in case of a constant
// a4 && a5 <=> a6:
// forall n:[0, min(from_index,|haystack|-|needle|)].
// !contains || n > offset ==>
// forall n:[0, min(from_index, |haystack| - |needle|)].
// !contains || (n > offset) ==>
// haystack[n] != needle[0] || ... ||
// haystack[n+|needle|-1] != needle[|needle|-1]
symbol_exprt qvar2=fresh_univ_index("QA_index_of_string_2", index_type);
Expand All @@ -273,6 +275,7 @@ exprt string_constraint_generatort::add_axioms_for_last_index_of_string(

or_exprt premise(
not_exprt(contains), binary_relation_exprt(qvar2, ID_gt, offset));

string_constraintt a6(
qvar2,
from_integer(0, index_type),
Expand Down