Merge #47: Simplify field impl selection

c6cff39 Simplify switch/case and add breaks as necessary (Cory Fields)
42883b7 Move clmul runtime detection to a function (Cory Fields)

Pull request description:

  For context see: #46

  In addition to adding the missing breaks, this disentangles the cases.

ACKs for top commit:
  sipa:
    ACK c6cff39

Tree-SHA512: 54bd57dde1c4960f2405f6d32676e8cda2fb91884ec93e9b566fb64ddb15821ea06410e592bc928d0443c617fb0f1427024f5256187b9e9d53f09148ad7e851e

Author: sipa

src/minisketch.cpp

@@ -62,6 +62,22 @@ enum class FieldImpl {
 #endif
 };
 
+static inline bool EnableClmul()
+{
+#ifdef HAVE_CLMUL
+#ifdef _MSC_VER
+    int regs[4];
+    __cpuid(regs, 1);
+    return (regs[2] & 0x2);
+#else
+    uint32_t eax, ebx, ecx, edx;
+    return (__get_cpuid(1, &eax, &ebx, &ecx, &edx) && (ecx & 0x2));
+#endif
+#else
+    return false;
+#endif
+}
+
 Sketch* Construct(int bits, int impl)
 {
     switch (FieldImpl(impl)) {
@@ -86,47 +102,56 @@ Sketch* Construct(int bits, int impl)
         default:
             return nullptr;
         }
+        break;
 #ifdef HAVE_CLMUL
     case FieldImpl::CLMUL:
-    case FieldImpl::CLMUL_TRI: {
-#ifdef _MSC_VER
-        int regs[4];
-        __cpuid(regs, 1);
-        if (regs[2] & 0x2) {
-#else
-        uint32_t eax, ebx, ecx, edx;
-        if (__get_cpuid(1, &eax, &ebx, &ecx, &edx) && (ecx & 0x2)) {
-#endif
+        if (EnableClmul()) {
             switch ((bits + 7) / 8) {
             case 1:
-                if (FieldImpl(impl) == FieldImpl::CLMUL) return ConstructClMul1Byte(bits, impl);
-                if (FieldImpl(impl) == FieldImpl::CLMUL_TRI) return ConstructClMulTri1Byte(bits, impl);
+                return ConstructClMul1Byte(bits, impl);
             case 2:
-                if (FieldImpl(impl) == FieldImpl::CLMUL) return ConstructClMul2Bytes(bits, impl);
-                if (FieldImpl(impl) == FieldImpl::CLMUL_TRI) return ConstructClMulTri2Bytes(bits, impl);
+                return ConstructClMul2Bytes(bits, impl);
             case 3:
-                if (FieldImpl(impl) == FieldImpl::CLMUL) return ConstructClMul3Bytes(bits, impl);
-                if (FieldImpl(impl) == FieldImpl::CLMUL_TRI) return ConstructClMulTri3Bytes(bits, impl);
+                return ConstructClMul3Bytes(bits, impl);
             case 4:
-                if (FieldImpl(impl) == FieldImpl::CLMUL) return ConstructClMul4Bytes(bits, impl);
-                if (FieldImpl(impl) == FieldImpl::CLMUL_TRI) return ConstructClMulTri4Bytes(bits, impl);
+                return ConstructClMul4Bytes(bits, impl);
             case 5:
-                if (FieldImpl(impl) == FieldImpl::CLMUL) return ConstructClMul5Bytes(bits, impl);
-                if (FieldImpl(impl) == FieldImpl::CLMUL_TRI) return ConstructClMulTri5Bytes(bits, impl);
+                return ConstructClMul5Bytes(bits, impl);
             case 6:
-                if (FieldImpl(impl) == FieldImpl::CLMUL) return ConstructClMul6Bytes(bits, impl);
-                if (FieldImpl(impl) == FieldImpl::CLMUL_TRI) return ConstructClMulTri6Bytes(bits, impl);
+                return ConstructClMul6Bytes(bits, impl);
             case 7:
-                if (FieldImpl(impl) == FieldImpl::CLMUL) return ConstructClMul7Bytes(bits, impl);
-                if (FieldImpl(impl) == FieldImpl::CLMUL_TRI) return ConstructClMulTri7Bytes(bits, impl);
+                return ConstructClMul7Bytes(bits, impl);
             case 8:
-                if (FieldImpl(impl) == FieldImpl::CLMUL) return ConstructClMul8Bytes(bits, impl);
-                if (FieldImpl(impl) == FieldImpl::CLMUL_TRI) return ConstructClMulTri8Bytes(bits, impl);
+                return ConstructClMul8Bytes(bits, impl);
             default:
                 return nullptr;
             }
         }
-    }
+        break;
+    case FieldImpl::CLMUL_TRI:
+        if (EnableClmul()) {
+            switch ((bits + 7) / 8) {
+            case 1:
+                return ConstructClMulTri1Byte(bits, impl);
+            case 2:
+                return ConstructClMulTri2Bytes(bits, impl);
+            case 3:
+                return ConstructClMulTri3Bytes(bits, impl);
+            case 4:
+                return ConstructClMulTri4Bytes(bits, impl);
+            case 5:
+                return ConstructClMulTri5Bytes(bits, impl);
+            case 6:
+                return ConstructClMulTri6Bytes(bits, impl);
+            case 7:
+                return ConstructClMulTri7Bytes(bits, impl);
+            case 8:
+                return ConstructClMulTri8Bytes(bits, impl);
+            default:
+                return nullptr;
+            }
+        }
+        break;
 #endif
     }
     return nullptr;