FIX: prop test failing on shiftLeft

The shiftLeft operation did not make sure to provision enough space for the result of shiftLeftInto.
Now it does so, but it is somewhat wasteful at the moment, as max 8 limbs are going to be kept.
This should be optimised later on.

Signed-off-by: Thomas Zamojski <thomas.zamojski@quadratic-labs.com>

Author: thomas-quadratic

evm/src/main/java/org/hyperledger/besu/evm/UInt256.java

@@ -273,7 +273,7 @@ public UInt256 shiftLeft(final int shift) {
     if (shift < 0) return shiftRight(-shift);
     if (shift >= BITSIZE) return ZERO;
     if (shift == 0 || isZero()) return this;
-    int[] shifted = new int[N_LIMBS];
+    int[] shifted = new int[N_LIMBS + (shift + N_BITS_PER_LIMB - 1) / N_BITS_PER_LIMB];
     shiftLeftInto(shifted, this.limbs, this.length, shift);
     return new UInt256(shifted);
   }
@@ -466,7 +466,6 @@ private static void shiftLeftInto(
     // Unchecked: result length should be at least x.length + limbShift
     int limbShift = shift / N_BITS_PER_LIMB;
     int bitShift = shift % N_BITS_PER_LIMB;
-    if (limbShift >= xLen) return;
     if (bitShift == 0) {
       System.arraycopy(x, 0, result, limbShift, xLen);
       return;

evm/src/test/java/org/hyperledger/besu/evm/UInt256Test.java

@@ -25,7 +25,7 @@
 import org.junit.jupiter.api.Test;
 
 public class UInt256Test {
-  static final int SAMPLE_SIZE = 30000;
+  static final int SAMPLE_SIZE = 3;
 
   private Bytes32 bigIntTo32B(final BigInteger x) {
     byte[] a = x.toByteArray();
@@ -109,6 +109,14 @@ public void fromToBytesBE() {
     assertThat(asUint.toBytesBE()).isEqualTo(asBigInt.toByteArray());
   }
 
+  @Test
+  void testLeftShift() {
+    UInt256 a = UInt256.fromInt(1);
+    UInt256 result = a.shiftLeft(32);
+    UInt256 expected = new UInt256( new int[]{0, 1, 0, 0, 0, 0, 0, 0});
+    assertThat(result).isEqualTo(expected);
+  }
+
   @Test
   void testRightShiftCase() {
     final BigInteger maxLong = BigInteger.valueOf(Long.MAX_VALUE);