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Improve comments on backtrack implementations

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This commit is contained in:
lperron@google.com
2010-09-16 14:16:51 +00:00
parent a581431cdc
commit cd0c3f6e13
1 changed files with 19 additions and 19 deletions
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38
constraint_solver/constraint_solver.cc
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@@ -803,7 +803,7 @@ class Search {
// Jumps back to the previous choice point, Checks if it was correctly set.
void JumpBack();
void ClearBuffer() {
CHECK(jmpbuf_filled_);
CHECK(jmpbuf_filled_) << "Internal error in backtracking";
jmpbuf_filled_ = false;
}
@@ -825,37 +825,37 @@ class Search {
// Backtrack is implemented using 3 primitives:
// CP_TRY to start searching
// CP_DOFAIL to signal a failure. The program will continue on the CP_ONFAIL
// CP_DO_FAIL to signal a failure. The program will continue on the CP_ON_FAIL
// primitive.
// FAST_BACKTRACK protects an implementation of backtrack using
// setjmp/longjmp. The clean portable way is to use exception,
// CP_FAST_BACKTRACK protects an implementation of backtrack using
// setjmp/longjmp. The clean portable way is to use exceptions,
// unfortunately, it can be much slower. Thus we use ideas from
// Prolog and other CP/CLP implementation and implement failing and
// backtracking using setjmp/longjmp.
#define FAST_BACKTRACK
#if defined(FAST_BACKTRACK)
// We cannot use a method/function for this as we would loose the
// Prolog, CP/CLP implementations, continuations in C and implement failing
// and backtracking using setjmp/longjmp.
#define CP_FAST_BACKTRACK
#if defined(CP_FAST_BACKTRACK)
// We cannot use a method/function for this as we would lose the
// context in the setjmp implementation.
#define CP_TRY(search) \
CHECK(!search->jmpbuf_filled_) << "Fail() called outside search"; \
search->jmpbuf_filled_ = true; \
if (setjmp(search->fail_buffer_) == 0)
#define CP_ONFAIL else
#define CP_DOFAIL(search) longjmp(search->fail_buffer_, 0)
#else
#define CP_ON_FAIL else
#define CP_DO_FAIL(search) longjmp(search->fail_buffer_, 1)
#else // CP_FAST_BACKTRACK
class FailException {};
#define CP_TRY(search) \
CHECK(!search->jmpbuf_filled_) << "Fail() called outside search"; \
search->jmpbuf_filled_ = true; \
try
#define CP_ONFAIL catch(FailException&)
#define CP_DOFAIL(search) throw FailException()
#endif
#define CP_ON_FAIL catch(FailException&)
#define CP_DO_FAIL(search) throw FailException()
#endif // CP_FAST_BACKTRACK
void Search::JumpBack() {
ClearBuffer();
CP_DOFAIL(this);
CP_DO_FAIL(this);
}
void Search::SetBranchSelector(
@@ -1745,7 +1745,7 @@ bool Solver::NextSolution() {
PushSentinel(ROOT_NODE_SENTINEL);
state_ = IN_SEARCH;
search->ClearBuffer();
} CP_ONFAIL {
} CP_ON_FAIL {
queue_->Clear();
BacktrackToSentinel(INITIAL_SEARCH_SENTINEL);
state_ = PROBLEM_INFEASIBLE;
@@ -1827,7 +1827,7 @@ bool Solver::NextSolution() {
}
result = true;
finish = true;
} CP_ONFAIL {
} CP_ON_FAIL {
queue_->Clear();
if (search->should_finish()) {
fd = NULL;
@@ -1905,7 +1905,7 @@ bool Solver::CheckAssignment(Assignment* const solution) {
// TODO(user): Why INFEASIBLE?
state_ = PROBLEM_INFEASIBLE;
return true;
} CP_ONFAIL {
} CP_ON_FAIL {
Constraint* const ct = constraints_list_[constraints_];
if (ct->name().empty()) {
VLOG(1) << "Failing constraint = "