rework range check to be correct and faster

dotnet · Feb 16, 2021 · db49342 · db49342
1 parent 74b60ee
commit db49342
Showing 1 changed file with 9 additions and 7 deletions.
diff --git a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlTypes/SqlTypeWorkarounds.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlTypes/SqlTypeWorkarounds.cs
@@ -61,23 +61,25 @@ internal static DateTime SqlDateTimeToDateTime(int daypart, int timepart)
             const int SQLTicksPerMinute = SQLTicksPerSecond * 60;
             const int SQLTicksPerHour = SQLTicksPerMinute * 60;
             const int SQLTicksPerDay = SQLTicksPerHour * 24;
-            const int MinDay = -53690;                // Jan 1 1753
+            //const int MinDay = -53690;                // Jan 1 1753
+            const uint MinDayOffset = 53690;            // postive value of MinDay used to pull negative values up to 0 so a single check can be used
             const uint MaxDay = 2958463;               // Dec 31 9999 is this many days from Jan 1 1900
             const uint MaxTime = SQLTicksPerDay - 1; // = 25919999,  11:59:59:997PM
-            const int MinTime = 0;                    // 00:00:0:000PM
             const long BaseDateTicks = 599266080000000000L;//new DateTime(1900, 1, 1).Ticks;
 
-            if ((uint)daypart > MaxDay || (uint)timepart > MaxTime || daypart < MinDay || timepart < MinTime)
+            // casting to uint wraps negative values to large positive ones above the valid 
+            // ranges so the lower bound doesn't need to be checked
+            if ((uint)(daypart + MinDayOffset) > (MaxDay + MinDayOffset) || (uint)timepart > MaxTime)
             {
                 ThrowOverflowException();
             }
 
             long dayticks = daypart * TimeSpan.TicksPerDay;
             double timePartPerMs = timepart / SQLTicksPerMillisecond;
-            double int1 = timePartPerMs + 0.5;
-            long timeticks1 = ((long)int1) * TimeSpan.TicksPerMillisecond;
-            long ticks1 = BaseDateTicks + dayticks + timeticks1;
-            return new DateTime(ticks1);
+            timePartPerMs += 0.5;
+            long timeTicks = ((long)timePartPerMs) * TimeSpan.TicksPerMillisecond;
+            long totalTicks = BaseDateTicks + dayticks + timeTicks;
+            return new DateTime(totalTicks);
         }
 
         private static void ThrowOverflowException()