diff options
| -rw-r--r-- | rsa/common.py | 31 |
1 files changed, 29 insertions, 2 deletions
diff --git a/rsa/common.py b/rsa/common.py index 7c852b6..ecb42c9 100644 --- a/rsa/common.py +++ b/rsa/common.py @@ -8,10 +8,17 @@ def bit_size(number): >>> bit_size(1023) 10 >>> bit_size(1024) - 10 + 11 >>> bit_size(1025) 11 + >>> bit_size(1 << 1024) + 1025 + >>> bit_size((1 << 1024) + 1) + 1025 + >>> bit_size((1 << 1024) - 1) + 1024 + ''' if number < 0: @@ -20,12 +27,32 @@ def bit_size(number): if number == 0: return 1 - return int(math.ceil(math.log(number, 2))) + # This works, even with very large numbers. When using math.log(number, 2), + # you'll get rounding errors and it'll fail. + bits = 0 + while number: + bits += 1 + number >>= 1 + + return bits + def byte_size(number): """Returns the number of bytes required to hold a specific long number. The number of bytes is rounded up. + + >>> byte_size(1 << 1023) + 128 + >>> byte_size((1 << 1024) - 1) + 128 + >>> byte_size(1 << 1024) + 129 """ return int(math.ceil(bit_size(number) / 8.0)) + +if __name__ == '__main__': + import doctest + doctest.testmod() + |