Make 128-bit addition use 2*64 bit values

As opposed to 4*32 bit values.
Done for subtraction as well

presto-spi/src/main/java/io/prestosql/spi/type/UnscaledDecimal128Arithmetic.java

@@ -25,7 +25,6 @@
 import static io.prestosql.spi.type.Decimals.MAX_PRECISION;
 import static io.prestosql.spi.type.Decimals.longTenToNth;
 import static java.lang.Integer.toUnsignedLong;
-import static java.lang.String.format;
 import static java.lang.System.arraycopy;
 import static java.util.Arrays.fill;
 
@@ -353,77 +352,38 @@ else if (compare < 0) {
      */
     private static long addUnsignedReturnOverflow(Slice left, Slice right, Slice result, boolean resultNegative)
     {
-        // TODO: consider two 7 bytes operations
-        int l0 = getInt(left, 0);
-        int l1 = getInt(left, 1);
-        int l2 = getInt(left, 2);
-        int l3 = getInt(left, 3);
+        long l0 = getLong(left, 0);
+        long l1 = getLong(left, 1);
 
-        int r0 = getInt(right, 0);
-        int r1 = getInt(right, 1);
-        int r2 = getInt(right, 2);
-        int r3 = getInt(right, 3);
+        long r0 = getLong(right, 0);
+        long r1 = getLong(right, 1);
 
-        long intermediateResult;
-        intermediateResult = toUnsignedLong(l0) + toUnsignedLong(r0);
+        long z0 = l0 + r0;
+        int overflow = unsignedIsSmaller(z0, l0) ? 1 : 0;
 
-        int z0 = (int) intermediateResult;
+        long intermediateResult = l1 + r1 + overflow;
+        long z1 = intermediateResult & (~SIGN_LONG_MASK);
+        pack(result, z0, z1, resultNegative);
 
-        intermediateResult = toUnsignedLong(l1) + toUnsignedLong(r1) + (intermediateResult >>> 32);
-
-        int z1 = (int) intermediateResult;
-
-        intermediateResult = toUnsignedLong(l2) + toUnsignedLong(r2) + (intermediateResult >>> 32);
-
-        int z2 = (int) intermediateResult;
-
-        intermediateResult = toUnsignedLong(l3) + toUnsignedLong(r3) + (intermediateResult >>> 32);
-
-        int z3 = (int) intermediateResult & (~SIGN_INT_MASK);
-
-        pack(result, z0, z1, z2, z3, resultNegative);
-
-        return intermediateResult >> 31;
+        return intermediateResult >>> 63;
     }
 
     /**
      * This method ignores signs of the left and right and assumes that left is greater then right
      */
     private static void subtractUnsigned(Slice left, Slice right, Slice result, boolean resultNegative)
     {
-        // TODO: consider two 7 bytes operations
-        int l0 = getInt(left, 0);
-        int l1 = getInt(left, 1);
-        int l2 = getInt(left, 2);
-        int l3 = getInt(left, 3);
-
-        int r0 = getInt(right, 0);
-        int r1 = getInt(right, 1);
-        int r2 = getInt(right, 2);
-        int r3 = getInt(right, 3);
-
-        long intermediateResult;
-        intermediateResult = toUnsignedLong(l0) - toUnsignedLong(r0);
-
-        int z0 = (int) intermediateResult;
-
-        intermediateResult = toUnsignedLong(l1) - toUnsignedLong(r1) + (intermediateResult >> 32);
+        long l0 = getLong(left, 0);
+        long l1 = getLong(left, 1);
 
-        int z1 = (int) intermediateResult;
+        long r0 = getLong(right, 0);
+        long r1 = getLong(right, 1);
 
-        intermediateResult = toUnsignedLong(l2) - toUnsignedLong(r2) + (intermediateResult >> 32);
+        long z0 = l0 - r0;
+        int underflow = unsignedIsSmaller(l0, z0) ? 1 : 0;
+        long z1 = l1 - r1 - underflow;
 
-        int z2 = (int) intermediateResult;
-
-        intermediateResult = toUnsignedLong(l3) - toUnsignedLong(r3) + (intermediateResult >> 32);
-
-        int z3 = (int) intermediateResult;
-
-        pack(result, z0, z1, z2, z3, resultNegative);
-
-        if ((intermediateResult >> 32) != 0) {
-            throw new IllegalStateException(format("Non empty carry over after subtracting [%d]. right > left?", (intermediateResult >> 32)));
-        }
+        pack(result, z0, z1, resultNegative);
     }
 
     public static Slice multiply(Slice left, Slice right)
@@ -1737,6 +1697,14 @@ private static void setRawLong(Slice decimal, int index, long value)
         decimal.setLong(SIZE_OF_LONG * index, value);
     }
 
+    /**
+     * Based on Long.compareUnsigned()
+     */
+    private static boolean unsignedIsSmaller(long first, long second)
+    {
+        return first + Long.MIN_VALUE < second + Long.MIN_VALUE;
+    }
+
     private static void checkArgument(boolean condition)
     {
         if (!condition) {