Added MULH test

tests/mulh.s

@@ -0,0 +1,40 @@
+.include "exit_return.s"
+
+.global _start
+_start:
+    # Set base value of a0 to 'test failed'
+    addi a0, zero, 1
+
+    # Multiply 2 * 3 in t0, high bits
+    addi t0, zero, 3
+    addi t1, zero, 2
+    mulh t0, t0, t1
+    addi t1, zero, 0
+    beq t0, t1, mulh_low_ok
+    exret
+
+mulh_low_ok:
+    # Multiply 2<<29 * 8 in t0, high bits
+    # Result high should be 2
+    addi t1, zero, 2
+    slli t0, t1, 29
+    addi t1, zero, 8
+    mulh t0, t0, t1
+    addi t1, zero, 2
+    beq t0, t1, mulh_high_ok
+    exret
+
+mulh_high_ok:
+    # Multiply 2 << 29 * -8 in t0, high bits
+    # Result high should be 0xFFFF_FFFE ie -2 signed ?
+    addi t1, zero, 2
+    slli t0, t1, 29
+    addi t1, zero, -8
+    mulh t0, t0, t1
+    addi t1, zero, -2
+    beq t0, t1, mulh_neg_ok
+    exret
+
+mulh_neg_ok:
+    addi a0, zero, 0
+    exret

tests/test.sh

@@ -29,3 +29,4 @@ test "BLT  : Branch Less Than       " "../build/tests/blt  " 0
 test "JAL  : Jump And Link          " "../build/tests/jal  " 0
 test "SWLW : Store Word Load Word   " "../build/tests/swlw " 0
 test "JALR : Jump And Link Register " "../build/tests/jalr " 0
+test "MULH : MULtply High           " "../build/tests/mulh " 0