fixed a bug in BGV parameter estimation logic

src/pke/lib/scheme/bgvrns/bgvrns-parametergeneration.cpp

@@ -455,12 +455,15 @@ bool ParameterGenerationBGVRNS::ParamsGenBGVRNS(std::shared_ptr<CryptoParameters
         auxTowers = std::get<1>(hybridKSInfo);
     }
 
-    // when the scaling technique is not FIXED_MANUAL, set a small value so that the rest of the logic could go through
+    // when the scaling technique is not FIXEDMANUAL (and not FLEXIBLEAUTOEXT),
+    // set a small value so that the rest of the logic could go through (this is a workaround)
+    // TODO we should uncouple the logic of FIXEDMANUAL and all FLEXIBLE MODES; some of the code above should be moved
+    // to the branch for FIXEDMANUAL
     if (qBound == 0)
         qBound = 20;
 
+    // HE Standards compliance logic/check
     uint32_t n = computeRingDimension(cryptoParams, qBound, cyclOrder);
-    // End HE Standards compliance logic/check
 
     uint32_t vecSize = (scalTech != FLEXIBLEAUTOEXT) ? numPrimes : numPrimes + 1;
     std::vector<NativeInteger> moduliQ(vecSize);
@@ -471,7 +474,10 @@ bool ParameterGenerationBGVRNS::ParamsGenBGVRNS(std::shared_ptr<CryptoParameters
         auto moduliInfo    = computeModuli(cryptoParams, n, evalAddCount, keySwitchCount, auxTowers, numPrimes);
         moduliQ            = std::get<0>(moduliInfo);
         uint32_t newQBound = std::get<1>(moduliInfo);
-        while (qBound < newQBound) {
+
+        // the counter makes sure the first iteration of the while loop is always run
+        uint32_t counter = 0;
+        while ((counter == 0) || (qBound < newQBound)) {
             qBound          = newQBound;
             n               = computeRingDimension(cryptoParams, newQBound, cyclOrder);
             auto moduliInfo = computeModuli(cryptoParams, n, evalAddCount, keySwitchCount, auxTowers, numPrimes);
@@ -487,6 +493,7 @@ bool ParameterGenerationBGVRNS::ParamsGenBGVRNS(std::shared_ptr<CryptoParameters
                     (scalTech == FLEXIBLEAUTOEXT) ? moduliQ.size() - 1 : moduliQ.size(), auxBits);
                 newQBound += std::get<0>(hybridKSInfo);
             }
+            counter++;
         }
         cyclOrder    = 2 * n;
         modulusOrder = getCyclicOrder(n, ptm, scalTech);
@@ -496,6 +503,7 @@ bool ParameterGenerationBGVRNS::ParamsGenBGVRNS(std::shared_ptr<CryptoParameters
         }
     }
     else {
+        // FIXEDMANUAL mode
         cyclOrder = 2 * n;
         // For ModulusSwitching to work we need the moduli to be also congruent to 1 modulo ptm
         usint plaintextModulus = ptm;