Use uint in ProfLazyMode test when measuring time delta.

test/cctest/test-log.cc

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 //
 // Tests of logging functions from log.h
 
 #ifdef ENABLE_LOGGING_AND_PROFILING
 
 #include "v8.h"
 
 #include "log.h"
 #include "cctest.h"
@@ skipping 148 matching lines @@
   buffer[map_log_size] = '\0';
   const char* code_creation = "\ncode-creation,";  // eq. to /^code-creation,/
   CHECK_NE(NULL, strstr(buffer.start(), code_creation));
 
   // Force compiler to generate new code by parametrizing source.
   EmbeddedVector<char, 100> script_src;
   i::OS::SNPrintF(script_src,
                   "for (var i = 0; i < 1000; ++i) { "
                   "(function(x) { return %d * x; })(i); }",
                   log_pos);
-  // Run code for 200 msecs to get some ticks.
-  const int64_t started_us = i::OS::Ticks();
-  while (i::OS::Ticks() - started_us < 200 * 1000) {
+  // Run code for 200 msecs to get some ticks. Use uint to always have
+  // non-negative delta.
+  const uint64_t started_us = i::OS::Ticks();
+  uint64_t delta;
+  while ((delta = i::OS::Ticks() - started_us) < 200 * 1000) {

[William Hesse, 2009/05/29 12:19:49]

The condition should really be
(ended_us = ticks()) < started_us + 200 * 1000)
delta_us = ended_us - started_us;
in order to correctly compare unsigneds, because the difference of two unsigneds
cannot be negative.

[William Hesse, 2009/05/29 12:55:32]

Actually, we don't really understand what is going on.  I think converting to
unsigned is the wrong idea, though.  OS::Ticks should not be anywhere near the
negative range, and tv_secs and tv_usecs (used in GetTimeOfDay, used by
OS::Ticks) should also be safe.

I think the best practice is to put two times you want to compare on opposite
sides of the comparison operator, rather than subtracting them.  It should be
fine to leave them as ints, too.

if (end_time < start_time + desired delta)
is valid as long as end_time and start_time + desired delta
are in the valid range of the type.

But I don't see how the change to uint is supposed to help.

     CompileAndRunScript(script_src.start());
   }
 
   Logger::PauseProfiler();
   CHECK(!LoggerTestHelper::IsSamplerActive());
 
   // Now we must have compiler and tick records.
   int log_size = GetLogLines(log_pos, &buffer);
   printf("log_size: %d\n", log_size);
   CHECK_GT(log_size, 0);
@@ skipping 517 matching lines @@
   // Make sure that all log data is written prior crash due to CHECK failure.
   fflush(stdout);
   CHECK(results_equal);
 
   env->Exit();
   Logger::TearDown();
   i::FLAG_always_compact = saved_always_compact;
 }
 
 #endif  // ENABLE_LOGGING_AND_PROFILING