bignum_core.py: Add "BignumCoreShiftL()"

This patch introduces automatic test input generation for
`mpi_core_shift_l()` function.

It also adds two utility functions in bignum_common.

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>

scripts/mbedtls_dev/bignum_common.py

@@ -80,6 +80,23 @@ def hex_digits_for_limb(limbs: int, bits_in_limb: int) -> int:
     """ Retrun the hex digits need for a number of limbs. """
     return 2 * (limbs * bits_in_limb // 8)
 
+def hex_digits_max_int(val: str, bits_in_limb: int) -> int:
+    """ Return the first number exceeding maximum  the limb space
+    required to store the input hex-string value. This method
+    weights on the input str_len rather than numerical value
+    and works with zero-padded inputs"""
+    n = ((1 << (len(val) * 4)) - 1)
+    l = limbs_mpi(n, bits_in_limb)
+    return bound_mpi_limbs(l, bits_in_limb)
+
+def zfill_match(reference: str, target: str) -> str:
+    """ Zero pad target hex-string the match the limb size of
+    the refference input """
+    lt = len(target)
+    lr = len(reference)
+    targen_len = lr if lt < lr else lt
+    return "{:x}".format(int(target, 16)).zfill(targen_len)
+
 class OperationCommon(test_data_generation.BaseTest):
     """Common features for bignum binary operations.
 

scripts/mbedtls_dev/bignum_core.py

@@ -68,6 +68,68 @@ class BignumCoreShiftR(BignumCoreTarget, test_data_generation.BaseTest):
             for count in counts:
                 yield cls(input_hex, descr, count).create_test_case()
 
+
+class BignumCoreShiftL(BignumCoreTarget, bignum_common.ModOperationCommon):
+    """Test cases for mbedtls_bignum_core_shift_l()."""
+
+    BIT_SHIFT_VALUES = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a',
+                        '1f', '20', '21', '3f', '40', '41', '47', '48', '4f',
+                        '50', '51', '58', '80', '81', '88']
+    DATA = ["0", "1", "40", "dee5ca1a7ef10a75", "a1055eb0bb1efa1150ff",
+            "002e7ab0070ad57001", "020100000000000000001011121314151617",
+            "1946e2958a85d8863ae21f4904fcc49478412534ed53eaf321f63f2a222"
+            "7a3c63acbf50b6305595f90cfa8327f6db80d986fe96080bcbb5df1bdbe"
+            "9b74fb8dedf2bddb3f8215b54dffd66409323bcc473e45a8fe9d08e77a51"
+            "1698b5dad0416305db7fcf"]
+    arity = 1
+    test_function = "mpi_core_shift_l"
+    test_name = "Core shift(L)"
+    input_style = "arch_split"
+    symbol = "<<"
+    input_values = BIT_SHIFT_VALUES
+    moduli = DATA
+
+    @property
+    def val_n_max_limbs(self) -> int:
+        """ Return the limb count required to store the maximum number that can
+        fit in a the number of digits used by val_n """
+        m = bignum_common.hex_digits_max_int(self.val_n, self.bits_in_limb) - 1
+        return bignum_common.limbs_mpi(m, self.bits_in_limb)
+
+    def arguments(self) -> List[str]:
+        return [bignum_common.quote_str(self.val_n),
+                str(self.int_a)
+                ] + self.result()
+
+    def description(self) -> str:
+        """ Format the output as:
+        #{count} {hex input} ({input bits} {limbs capacity}) << {bit shift} """
+        bits = "({} bits in {} limbs)".format(self.int_n.bit_length(), self.val_n_max_limbs)
+        return "{} #{} {} {} {} {}".format(self.test_name,
+                                           self.count,
+                                           self.val_n,
+                                           bits,
+                                           self.symbol,
+                                           self.int_a)
+
+    def format_result(self, res: int) -> str:
+        # Override to match zero-pading for leading digits between the output and input.
+        res_str = bignum_common.zfill_match(self.val_n, "{:x}".format(res))
+        return bignum_common.quote_str(res_str)
+
+    def result(self) -> List[str]:
+        result = (self.int_n << self.int_a)
+        # Calculate if there is space for shifting to the left(leading zero limbs)
+        mx = bignum_common.hex_digits_max_int(self.val_n, self.bits_in_limb)
+        # If there are empty limbs ahead, adjust the bitmask accordingly
+        result = result & (self.r - 1) if mx == self.r else result & (mx - 1)
+        return [self.format_result(result)]
+
+    @property
+    def is_valid(self) -> bool:
+        return True
+
+
 class BignumCoreCTLookup(BignumCoreTarget, test_data_generation.BaseTest):
     """Test cases for mbedtls_mpi_core_ct_uint_table_lookup()."""
     test_function = "mpi_core_ct_uint_table_lookup"