fraction_timespec::normalize(): Fix underflow case, allow multiple of ns_per_sec

2 files changed, 37 insertions, 4 deletions

diff --git a/include/jau/fraction_type.hpp b/include/jau/fraction_type.hpp
index d3c43bb..bbc32f8 100644
--- a/include/jau/fraction_type.hpp
+++ b/include/jau/fraction_type.hpp
@@ -931,8 +931,9 @@ namespace jau {
             using namespace jau::int_literals;
             const int64_t ns_per_sec = 1'000'000'000_i64;
             if( tv_nsec < 0 ) {
-                tv_nsec += ns_per_sec;
-                tv_sec -= 1;
+                const int64_t c = 1 + abs( tv_nsec ) / ns_per_sec;
+                tv_nsec += c * ns_per_sec;
+                tv_sec -= c;
             } else if( tv_nsec >= ns_per_sec ) {
                 const int64_t c = tv_nsec / ns_per_sec;
                 tv_nsec -= c * ns_per_sec;
@@ -948,8 +949,8 @@ namespace jau {
          * @return reference to this instance, normalized
          */
         constexpr fraction_timespec& operator+=(const fraction_timespec& rhs ) noexcept {
+            tv_nsec += rhs.tv_nsec; // we allow the 'overflow' over 1'000'000'000, fitting into type and normalize() later
             tv_sec += rhs.tv_sec;
-            tv_nsec += rhs.tv_nsec;
             return normalize();
         }
 
@@ -960,8 +961,8 @@ namespace jau {
          * @return reference to this instance, normalized
          */
         constexpr fraction_timespec& operator-=(const fraction_timespec& rhs ) noexcept {
+            tv_nsec -= rhs.tv_nsec; // we allow the 'overflow' over 1'000'000'000, fitting into type and normalize() later
             tv_sec -= rhs.tv_sec;
-            tv_nsec -= rhs.tv_nsec;
             return normalize();
         }
 
diff --git a/test/test_fractions_01.cpp b/test/test_fractions_01.cpp
index bdb3f00..2545635 100644
--- a/test/test_fractions_01.cpp
+++ b/test/test_fractions_01.cpp
@@ -616,6 +616,38 @@ TEST_CASE( "struct timespec type validation Test 03.00", "[fraction][struct_time
 
 
 TEST_CASE( "Fraction Time Arithmetic Add Test 03.1", "[fraction][fraction_timespec][add]" ) {
+    const int64_t ns_per_sec = 1'000'000'000_i64;
+
+    // 12.4 + 12.4 = 24.8 w/ double overflow in tv_nsec
+    {
+        fraction_timespec a ( 10_i64, 2 * ns_per_sec + 400000000_i64 );
+        fraction_timespec b ( 10_i64, 2 * ns_per_sec + 400000000_i64 );
+        fraction_timespec exp_sum (  24_i64, 800000000_i64 );
+        INFO_STR(" a " + a.to_string() );
+        INFO_STR(" b " + b.to_string() );
+        INFO_STR(" a+b " + (a+b).to_string() );
+        REQUIRE( ( a + b ) == exp_sum );
+    }
+    // 13.4 - 3.4 = 10.0 w/ double overflow in tv_nsec
+    {
+        fraction_timespec a ( 13_i64,                  400000000_i64 );
+        fraction_timespec b (  1_i64, 2 * ns_per_sec + 400000000_i64 );
+        fraction_timespec exp_sum (  10_i64, 0_i64 );
+        INFO_STR(" a " + a.to_string() );
+        INFO_STR(" b " + b.to_string() );
+        INFO_STR(" a-b " + (a-b).to_string() );
+        REQUIRE( ( a - b ) == exp_sum );
+    }
+    // 12.0 - 1.9 = 10.1 w/ double overflow in tv_nsec
+    {
+        fraction_timespec a ( 12_i64,                           0_i64 );
+        fraction_timespec b (  3_i64, -2 * ns_per_sec + 900000000_i64 );
+        fraction_timespec exp_sum (  10_i64, 100000000_i64 );
+        INFO_STR(" a " + a.to_string() );
+        INFO_STR(" b " + b.to_string() );
+        INFO_STR(" a-b " + (a-b).to_string() );
+        REQUIRE( ( a - b ) == exp_sum );
+    }
     // 10.4 + 0.4 = 10.8
     {
         fraction_timespec a ( 10_i64, 400000000_i64 );