Added CatIKS Koga's opt

include/keyswitch.hpp

@@ -60,11 +60,11 @@ void IdentityKeySwitch(TLWE<typename P::targetP> &res,
                            (j + 1) * P::basebit)) &
                 mask)-halfbase;
             if(aij > 0)
-            for (int k = 0; k <= P::targetP::k * P::targetP::n; k++)
-                res[k] -= ksk[i][j][aij - 1][k];
+                for (int k = 0; k <= P::targetP::k * P::targetP::n; k++)
+                    res[k] -= ksk[i][j][aij - 1][k];
             else if(aij < 0)
-            for (int k = 0; k <= P::targetP::k * P::targetP::n; k++)
-                res[k] += ksk[i][j][std::abs(aij) - 1][k];
+                for (int k = 0; k <= P::targetP::k * P::targetP::n; k++)
+                    res[k] += ksk[i][j][-aij - 1][k];
         }
     }
 }
@@ -75,13 +75,12 @@ void CatIdentityKeySwitch(
     const std::array<TLWE<typename P::domainP>, numcat> &tlwe,
     const KeySwitchingKey<P> &ksk)
 {
-    constexpr uint32_t mask = (1U << P::basebit) - 1;
     res = {};
     constexpr uint domain_digit =
         std::numeric_limits<typename P::domainP::T>::digits;
     constexpr uint target_digit =
         std::numeric_limits<typename P::targetP::T>::digits;
-    constexpr typename P::domainP::T prec_offset =
+    constexpr typename P::domainP::T roundoffset =
         (P::basebit * P::t) < domain_digit
             ? 1ULL << (domain_digit - (1 + P::basebit * P::t))
             : 0;
@@ -101,20 +100,27 @@ void CatIdentityKeySwitch(
                     tlwe[cat][P::domainP::k * P::domainP::n])
                 << (target_digit - domain_digit);
     }
+
+    //Koga's Optimization
+    constexpr typename P::domainP::T offset = iksoffsetgen<P>();
+    constexpr typename P::domainP::T mask = (1ULL << P::basebit) - 1; 
+    constexpr typename P::domainP::T halfbase = 1ULL << (P::basebit - 1);
     for (int i = 0; i < P::domainP::k * P::domainP::n; i++) {
         std::array<typename P::domainP::T, numcat> aibarcat;
         for (int cat = 0; cat < numcat; cat++)
-            aibarcat[cat] = tlwe[cat][i] + prec_offset;
+            aibarcat[cat] = tlwe[cat][i] + offset + roundoffset;
         for (int j = 0; j < P::t; j++) {
             for (int cat = 0; cat < numcat; cat++) {
-                const uint32_t aij =
-                    (aibarcat[cat] >>
-                     (std::numeric_limits<typename P::domainP::T>::digits -
-                      (j + 1) * P::basebit)) &
-                    mask;
-                if (aij != 0)
+                const int32_t aij =
+                ((aibar >> (std::numeric_limits<typename P::domainP::T>::digits -
+                           (j + 1) * P::basebit)) &
+                mask)-halfbase;
+                if (aij > 0)
                     for (int k = 0; k <= P::targetP::k * P::targetP::n; k++)
                         res[cat][k] -= ksk[i][j][aij - 1][k];
+                if (aij < 0)
+                    for (int k = 0; k <= P::targetP::k * P::targetP::n; k++)
+                        res[cat][k] += ksk[i][j][-aij - 1][k];
             }
         }
     }