Precision loss when calculating the TotalDuration, as a result, the last report result may not be added in output file

[cbuahin]

@WaterDesk reported the following issue #151

When I am using the latest official SWMM 5.2.4 code, and I found there was a bug fix have not been merged to the root repository which was pushed to https://github.com/pyswmm/Stormwater-Management-Model

The original PR is pyswmm#219, copy the details as below:

Precision loss when calculating the TotalDuration, as a result, the last report result may not be added in output file

SWMM version: 5.1.013

Reproduce Steps:

1. Use the sample INP file “Example1.inp”, make some changes:
   • END_TIME changes to 11:30 from 12:00
   • REPORT_STEP changes to 00:30:00 from 01:00:00
2. Open the changed "Example1.inp" file, then Run Simulation
3. Pick up a subcatchment or node or link, and Create a Time Series Table, then you will find the result data of the END_TIME has not been listed in the table. The current last one is Days 1 Hours 11:00:00, but not 11:30:00.

Analysis:

The Start/End Date and Time is stored as text in INP file, after parsing them from INP file, they will be converted to double values.

The EndTime “11:30:00’’ converts to 0.47916666666666669, when it is added with EndDate “01/02/1998” (35797.000000000000), the new EndDateTime is 35797.479166666664.
Use the below method to calculate the TotalDuration, the result is 127799.0.

    TotalDuration        = floor((EndDateTime - StartDateTime) * SECperDAY);

From the INP file, the StartDateTime is 01/01/1998 00:00:00, and the EndDateTime is 01/02/1998 11:30:00. The duration is 1 day and 11:30:00, it has 127800 seconds.

1 second precision losses now! So the last time result will never been reported in output file.

Solution:

The precision loss usually happens when a large double value plus a small double value. So, we need to avoid such calculations.

Change the calculation method of TotalDuration to be:

        double durationDate = EndDate - StartDate;
        double durationTime = EndTime - StartTime;
        TotalDuration = floor(durationDate * SECperDAY + durationTime * SECperDAY);