update windows build to Python 3.7

Lib/site-packages/asn1crypto/_perf/_big_num_ctypes.py

@@ -0,0 +1,69 @@
+# coding: utf-8
+
+"""
+ctypes interface for BN_mod_inverse() function from OpenSSL. Exports the
+following items:
+
+ - libcrypto
+    - BN_bn2bin()
+    - BN_CTX_free()
+    - BN_CTX_new()
+    - BN_free()
+    - BN_mod_inverse()
+    - BN_new()
+    - BN_num_bits()
+    - BN_set_negative()
+
+Will raise asn1crypto._ffi.LibraryNotFoundError() if libcrypto can not be
+found. Will raise asn1crypto._ffi.FFIEngineError() if there is an error
+interfacing with libcrypto.
+"""
+
+from __future__ import unicode_literals, division, absolute_import, print_function
+
+import sys
+
+from ctypes import CDLL, c_int, c_char_p, c_void_p
+from ctypes.util import find_library
+
+from .._ffi import LibraryNotFoundError, FFIEngineError
+
+
+try:
+    # On Python 2, the unicode string here may raise a UnicodeDecodeError as it
+    # tries to join a bytestring path to the unicode name "crypto"
+    libcrypto_path = find_library(b'crypto' if sys.version_info < (3,) else 'crypto')
+    if not libcrypto_path:
+        raise LibraryNotFoundError('The library libcrypto could not be found')
+
+    libcrypto = CDLL(libcrypto_path)
+
+    libcrypto.BN_new.argtypes = []
+    libcrypto.BN_new.restype = c_void_p
+
+    libcrypto.BN_bin2bn.argtypes = [c_char_p, c_int, c_void_p]
+    libcrypto.BN_bin2bn.restype = c_void_p
+
+    libcrypto.BN_bn2bin.argtypes = [c_void_p, c_char_p]
+    libcrypto.BN_bn2bin.restype = c_int
+
+    libcrypto.BN_set_negative.argtypes = [c_void_p, c_int]
+    libcrypto.BN_set_negative.restype = None
+
+    libcrypto.BN_num_bits.argtypes = [c_void_p]
+    libcrypto.BN_num_bits.restype = c_int
+
+    libcrypto.BN_free.argtypes = [c_void_p]
+    libcrypto.BN_free.restype = None
+
+    libcrypto.BN_CTX_new.argtypes = []
+    libcrypto.BN_CTX_new.restype = c_void_p
+
+    libcrypto.BN_CTX_free.argtypes = [c_void_p]
+    libcrypto.BN_CTX_free.restype = None
+
+    libcrypto.BN_mod_inverse.argtypes = [c_void_p, c_void_p, c_void_p, c_void_p]
+    libcrypto.BN_mod_inverse.restype = c_void_p
+
+except (AttributeError):
+    raise FFIEngineError('Error initializing ctypes')