Add an audit option to verify is_sorted (off by default) (#37)

Author: vedgy

README.md

@@ -127,6 +127,8 @@ conan install timsort/2.0.2
 
 A few configuration macros allow `gfx::timsort` and `gfx::timmerge` to emit diagnostic, which might be helpful to diagnose issues:
 * Defining `GFX_TIMSORT_ENABLE_ASSERT` inserts assertions in key locations in the algorithm to avoid logic errors.
+* Defining `GFX_TIMSORT_ENABLE_AUDIT` inserts assertions that verify pre- and postconditions. These verifications can slow the
+  algorithm down significantly. Enable the audit only while testing or debugging.
 * Defining `GFX_TIMSORT_ENABLE_LOG` inserts logs in key locations, which allow to follow more closely the flow of the algorithm.
 
 **cpp-TimSort** follows semantic versioning and provides the following macros to retrieve the current major, minor

include/gfx/timsort.hpp

@@ -45,13 +45,22 @@
 
 // Diagnostic selection macros
 
-#ifdef GFX_TIMSORT_ENABLE_ASSERT
+#if defined(GFX_TIMSORT_ENABLE_ASSERT) || defined(GFX_TIMSORT_ENABLE_AUDIT)
 #   include <cassert>
+#endif
+
+#ifdef GFX_TIMSORT_ENABLE_ASSERT
 #   define GFX_TIMSORT_ASSERT(expr) assert(expr)
 #else
 #   define GFX_TIMSORT_ASSERT(expr) ((void)0)
 #endif
 
+#ifdef GFX_TIMSORT_ENABLE_AUDIT
+#   define GFX_TIMSORT_AUDIT(expr) assert(expr)
+#else
+#   define GFX_TIMSORT_AUDIT(expr) ((void)0)
+#endif
+
 #ifdef GFX_TIMSORT_ENABLE_LOG
 #   include <iostream>
 #   define GFX_TIMSORT_LOG(expr) (std::clog << "# " << __func__ << ": " << expr << std::endl)
@@ -712,7 +721,10 @@ void timmerge(RandomAccessIterator first, RandomAccessIterator middle,
               RandomAccessIterator last, Compare compare, Projection projection) {
     typedef detail::projection_compare<Compare, Projection> compare_t;
     compare_t comp(std::move(compare), std::move(projection));
-    detail::TimSort<RandomAccessIterator, compare_t>::merge(first, middle, last, std::move(comp));
+    GFX_TIMSORT_AUDIT(std::is_sorted(first, middle, comp) && "Precondition");
+    GFX_TIMSORT_AUDIT(std::is_sorted(middle, last, comp) && "Precondition");
+    detail::TimSort<RandomAccessIterator, compare_t>::merge(first, middle, last, comp);
+    GFX_TIMSORT_AUDIT(std::is_sorted(first, last, comp) && "Postcondition");
 }
 
 /**
@@ -742,7 +754,8 @@ void timsort(RandomAccessIterator const first, RandomAccessIterator const last,
              Compare compare, Projection projection) {
     typedef detail::projection_compare<Compare, Projection> compare_t;
     compare_t comp(std::move(compare), std::move(projection));
-    detail::TimSort<RandomAccessIterator, compare_t>::sort(first, last, std::move(comp));
+    detail::TimSort<RandomAccessIterator, compare_t>::sort(first, last, comp);
+    GFX_TIMSORT_AUDIT(std::is_sorted(first, last, comp) && "Postcondition");
 }
 
 /**
@@ -790,6 +803,8 @@ void timsort(RandomAccessRange &range) {
 
 #undef GFX_TIMSORT_ENABLE_ASSERT
 #undef GFX_TIMSORT_ASSERT
+#undef GFX_TIMSORT_ENABLE_AUDIT
+#undef GFX_TIMSORT_AUDIT
 #undef GFX_TIMSORT_ENABLE_LOG
 #undef GFX_TIMSORT_LOG