fixed small errors in updated algo inside validatePayment

Author: parzival1821

service_contracts/src/FilecoinWarmStorageService.sol

@@ -1545,25 +1545,24 @@ contract FilecoinWarmStorageService is
 
         // Count proven epochs and find the last proven epoch
         uint256 provenEpochCount = 0;
-        uint256 lastProvenEpoch = 0;
+        uint256 lastProvenEpoch = fromEpoch;
 
 
         // Updated algorithm
         uint256 activationEpoch = provingActivationEpoch[dataSetId];
-        if(activationEpoch != 0 && toEpoch >= activationEpoch && toEpoch < block.number){
-            // now, starting epoch - fromEpoch + 1. find period corres to it. find out how long that period lasts and add that many epochs. then keep adding 2880 epochs till period end passes the endEpoch 
-
+        if(toEpoch >= activationEpoch && toEpoch < block.number){
+            // if `toEpoch` lies after activation, and `fromEpoch` lies before activation, then update the `fromEpoch`, as follows : 
             if(fromEpoch < activationEpoch){
-                fromEpoch = activationEpoch;
+                fromEpoch = activationEpoch - 1; // we have done -1 because starting epoch is considered as `fromEpoch + 1`
             }
 
             uint256 startingPeriod = getProvingPeriodForEpoch(dataSetId, fromEpoch + 1);
             uint256 endingPeriod = getProvingPeriodForEpoch(dataSetId, toEpoch);
 
-            // lets handle first period separately
+            // lets handle first period separately 
             uint256 startingPeriod_deadline = _calcPeriodDeadline(dataSetId, startingPeriod);
 
-            if(toEpoch < startingPeriod_deadline){
+            if(toEpoch < startingPeriod_deadline){ // alternative way to check the same : `startingPeriod == endingPeriod`
                 if(_isPeriodProven(dataSetId, startingPeriod)){
                     provenEpochCount = (toEpoch - fromEpoch);
                     lastProvenEpoch = toEpoch;
@@ -1575,7 +1574,7 @@ contract FilecoinWarmStorageService is
 
                 // now loop through the proving periods between endingPeriod and startingPeriod. 
                 for(uint256 period = startingPeriod + 1; period <= endingPeriod - 1; period++){
-                    if(provenPeriods[dataSetId][period]){ // here to check if period is proven, we can simply access the mapping since a period in between cannot be the current period 
+                    if(_isPeriodProven(dataSetId, period)){ 
                         provenEpochCount += maxProvingPeriod;
                         lastProvenEpoch = _calcPeriodDeadline(dataSetId, period);
                     }