Code and test clean up

Author: plokhotnyuk

jsoniter-scala-core/native/src/main/resources/scala-native/multiply_high.c

@@ -3,9 +3,7 @@
 #include <intrin.h>
 
 long long jsoniter_scala_multiply_high(long long x, long long y) {
-  long long high_product;
-  (void) _mul128(x, y, &high_product);
-  return high_product;
+  return __mulh(x, y);
 }
 
 unsigned long long jsoniter_scala_unsigned_multiply_high(unsigned long long x, unsigned long long y) {
@@ -24,22 +22,24 @@ unsigned long long jsoniter_scala_unsigned_multiply_high(unsigned long long x, u
 
 #else
 
+// Based on `int mulhs(int u, int v)` function from Hacker’s Delight 2nd Ed. by Henry S. Warren, Jr.
 long long jsoniter_scala_multiply_high(long long x, long long y) {
-  long long x0 = x & 0xffffffffL;
+  long long x0 = x & 0xFFFFFFFFL;
   long long x1 = x >> 32;
-  long long y0 = y & 0xffffffffL;
+  long long y0 = y & 0xFFFFFFFFL;
   long long y1 = y >> 32;
   long long t = x1 * y0 + ((unsigned long long) (x0 * y0) >> 32);
-  return x1 * y1 + (t >> 32) + (((t & 0xffffffffL) + x0 * y1) >> 32);
+  return x1 * y1 + (t >> 32) + (((t & 0xFFFFFFFFL) + x0 * y1) >> 32);
 }
 
+// Based on `unsigned mulhu(unsigned u, unsigned v)` function from Hacker’s Delight 2nd Ed. by Henry S. Warren, Jr.
 unsigned long long jsoniter_scala_unsigned_multiply_high(unsigned long long x, unsigned long long y) {
-  unsigned long long x0 = x & 0xffffffffL;
+  unsigned long long x0 = x & 0xFFFFFFFFL;
   unsigned long long x1 = x >> 32;
-  unsigned long long y0 = y & 0xffffffffL;
+  unsigned long long y0 = y & 0xFFFFFFFFL;
   unsigned long long y1 = y >> 32;
   unsigned long long t = x1 * y0 + ((x0 * y0) >> 32);
-  return x1 * y1 + (t >> 32) + (((t & 0xffffffffL) + x0 * y1) >> 32);
+  return x1 * y1 + (t >> 32) + (((t & 0xFFFFFFFFL) + x0 * y1) >> 32);
 }
 
 #endif

jsoniter-scala-core/native/src/test/scala/com/github/plokhotnyuk/jsoniter_scala/core/NativeMathSpec.scala

@@ -27,10 +27,6 @@ class NativeMathSpec extends AnyWordSpec with Matchers with ScalaCheckPropertyCh
     }
   }
 
-  def unsignedMultiplyHigh(x: Long, y: Long): Long = { // FIXME: replace by Math.unsignedMultiplyHigh after dropping JDK 17 support
-    var r = Math.multiplyHigh(x, y)
-    r += y & (x >> 63)
-    r += x & (y >> 63)
-    r
-  }
+  def unsignedMultiplyHigh(x: Long, y: Long): Long = // FIXME: replace by Math.unsignedMultiplyHigh after dropping JDK 17 support
+    Math.multiplyHigh(x, y) + (y & (x >> 63)) + (x & (y >> 63))
 }