Add module for bignum_core test generation

Separate file is added for classes used to generate cases for tests
in bignum_core.function. Common elements of the BignumOperation class
are added to classes in a new common file, for use across files.

Signed-off-by: Werner Lewis <werner.lewis@arm.com>

scripts/mbedtls_dev/bignum_common.py

@@ -0,0 +1,111 @@
+"""Common features for bignum in test generation framework."""
+# Copyright The Mbed TLS Contributors
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import itertools
+import typing
+
+from abc import abstractmethod
+from typing import Iterator, List, Tuple, TypeVar
+
+T = TypeVar('T') #pylint: disable=invalid-name
+
+def hex_to_int(val: str) -> int:
+    return int(val, 16) if val else 0
+
+def quote_str(val) -> str:
+    return "\"{}\"".format(val)
+
+def bound_mpi8(val: int) -> int:
+    """First number exceeding 8-byte limbs needed for given input value."""
+    return bound_mpi8_limbs(limbs_mpi8(val))
+
+def bound_mpi4(val: int) -> int:
+    """First number exceeding 4-byte limbs needed for given input value."""
+    return bound_mpi4_limbs(limbs_mpi4(val))
+
+def bound_mpi8_limbs(limbs: int) -> int:
+    """First number exceeding maximum of given 8-byte limbs."""
+    bits = 64 * limbs
+    return 1 << bits
+
+def bound_mpi4_limbs(limbs: int) -> int:
+    """First number exceeding maximum of given 4-byte limbs."""
+    bits = 32 * limbs
+    return 1 << bits
+
+def limbs_mpi8(val: int) -> int:
+    """Return the number of 8-byte limbs required to store value."""
+    return (val.bit_length() + 63) // 64
+
+def limbs_mpi4(val: int) -> int:
+    """Return the number of 4-byte limbs required to store value."""
+    return (val.bit_length() + 31) // 32
+
+def combination_pairs(values: List[T]) -> List[Tuple[T, T]]:
+    """Return all pair combinations from input values.
+
+    The return value is cast, as older versions of mypy are unable to derive
+    the specific type returned by itertools.combinations_with_replacement.
+    """
+    return typing.cast(
+        List[Tuple[T, T]],
+        list(itertools.combinations_with_replacement(values, 2))
+    )
+
+
+class OperationCommon:
+    """Common features for bignum binary operations.
+
+    This adds functionality common in binary operation tests.
+
+    Attributes:
+        symbol: Symbol to use for the operation in case description.
+        input_values: List of values to use as test case inputs. These are
+            combined to produce pairs of values.
+        input_cases: List of tuples containing pairs of test case inputs. This
+            can be used to implement specific pairs of inputs.
+    """
+    symbol = ""
+    input_values = [] # type: List[str]
+    input_cases = [] # type: List[Tuple[str, str]]
+
+    def __init__(self, val_a: str, val_b: str) -> None:
+        self.arg_a = val_a
+        self.arg_b = val_b
+        self.int_a = hex_to_int(val_a)
+        self.int_b = hex_to_int(val_b)
+
+    def arguments(self) -> List[str]:
+        return [quote_str(self.arg_a), quote_str(self.arg_b), self.result()]
+
+    @abstractmethod
+    def result(self) -> str:
+        """Get the result of the operation.
+
+        This could be calculated during initialization and stored as `_result`
+        and then returned, or calculated when the method is called.
+        """
+        raise NotImplementedError
+
+    @classmethod
+    def get_value_pairs(cls) -> Iterator[Tuple[str, str]]:
+        """Generator to yield pairs of inputs.
+
+        Combinations are first generated from all input values, and then
+        specific cases provided.
+        """
+        yield from combination_pairs(cls.input_values)
+        yield from cls.input_cases