summaryrefslogtreecommitdiffstats
path: root/Lib/base64.py
diff options
context:
space:
mode:
authorSerhiy Storchaka <storchaka@gmail.com>2013-05-19 08:49:32 (GMT)
committerSerhiy Storchaka <storchaka@gmail.com>2013-05-19 08:49:32 (GMT)
commit87aa7dc211451c0858f4f8cf7adae2de2a16e8fa (patch)
tree742d404abae2097186aae3fa5b9a46dce1152abb /Lib/base64.py
parentfef34e318697e53ea1b39a5da02308acdc5367f4 (diff)
parent2c3f2f19df0939744774370369b55e3ca214040c (diff)
downloadcpython-87aa7dc211451c0858f4f8cf7adae2de2a16e8fa.zip
cpython-87aa7dc211451c0858f4f8cf7adae2de2a16e8fa.tar.gz
cpython-87aa7dc211451c0858f4f8cf7adae2de2a16e8fa.tar.bz2
Issue #17812: Fixed quadratic complexity of base64.b32encode().
Optimize base64.b32encode() and base64.b32decode() (speed up to 3x).
Diffstat (limited to 'Lib/base64.py')
-rwxr-xr-xLib/base64.py125
1 files changed, 48 insertions, 77 deletions
diff --git a/Lib/base64.py b/Lib/base64.py
index 4042f00..0f731fa 100755
--- a/Lib/base64.py
+++ b/Lib/base64.py
@@ -138,21 +138,10 @@ def urlsafe_b64decode(s):
# Base32 encoding/decoding must be done in Python
-_b32alphabet = {
- 0: b'A', 9: b'J', 18: b'S', 27: b'3',
- 1: b'B', 10: b'K', 19: b'T', 28: b'4',
- 2: b'C', 11: b'L', 20: b'U', 29: b'5',
- 3: b'D', 12: b'M', 21: b'V', 30: b'6',
- 4: b'E', 13: b'N', 22: b'W', 31: b'7',
- 5: b'F', 14: b'O', 23: b'X',
- 6: b'G', 15: b'P', 24: b'Y',
- 7: b'H', 16: b'Q', 25: b'Z',
- 8: b'I', 17: b'R', 26: b'2',
- }
-
-_b32tab = [v[0] for k, v in sorted(_b32alphabet.items())]
-_b32rev = dict([(v[0], k) for k, v in _b32alphabet.items()])
-
+_b32alphabet = b'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567'
+_b32tab = [bytes([i]) for i in _b32alphabet]
+_b32tab2 = [a + b for a in _b32tab for b in _b32tab]
+_b32rev = {v: k for k, v in enumerate(_b32alphabet)}
def b32encode(s):
"""Encode a byte string using Base32.
@@ -161,41 +150,30 @@ def b32encode(s):
"""
if not isinstance(s, bytes_types):
raise TypeError("expected bytes, not %s" % s.__class__.__name__)
- quanta, leftover = divmod(len(s), 5)
+ leftover = len(s) % 5
# Pad the last quantum with zero bits if necessary
if leftover:
s = s + bytes(5 - leftover) # Don't use += !
- quanta += 1
- encoded = bytes()
- for i in range(quanta):
- # c1 and c2 are 16 bits wide, c3 is 8 bits wide. The intent of this
- # code is to process the 40 bits in units of 5 bits. So we take the 1
- # leftover bit of c1 and tack it onto c2. Then we take the 2 leftover
- # bits of c2 and tack them onto c3. The shifts and masks are intended
- # to give us values of exactly 5 bits in width.
- c1, c2, c3 = struct.unpack('!HHB', s[i*5:(i+1)*5])
- c2 += (c1 & 1) << 16 # 17 bits wide
- c3 += (c2 & 3) << 8 # 10 bits wide
- encoded += bytes([_b32tab[c1 >> 11], # bits 1 - 5
- _b32tab[(c1 >> 6) & 0x1f], # bits 6 - 10
- _b32tab[(c1 >> 1) & 0x1f], # bits 11 - 15
- _b32tab[c2 >> 12], # bits 16 - 20 (1 - 5)
- _b32tab[(c2 >> 7) & 0x1f], # bits 21 - 25 (6 - 10)
- _b32tab[(c2 >> 2) & 0x1f], # bits 26 - 30 (11 - 15)
- _b32tab[c3 >> 5], # bits 31 - 35 (1 - 5)
- _b32tab[c3 & 0x1f], # bits 36 - 40 (1 - 5)
- ])
+ encoded = bytearray()
+ from_bytes = int.from_bytes
+ b32tab2 = _b32tab2
+ for i in range(0, len(s), 5):
+ c = from_bytes(s[i: i + 5], 'big')
+ encoded += (b32tab2[c >> 30] + # bits 1 - 10
+ b32tab2[(c >> 20) & 0x3ff] + # bits 11 - 20
+ b32tab2[(c >> 10) & 0x3ff] + # bits 21 - 30
+ b32tab2[c & 0x3ff] # bits 31 - 40
+ )
# Adjust for any leftover partial quanta
if leftover == 1:
- return encoded[:-6] + b'======'
+ encoded[-6:] = b'======'
elif leftover == 2:
- return encoded[:-4] + b'===='
+ encoded[-4:] = b'===='
elif leftover == 3:
- return encoded[:-3] + b'==='
+ encoded[-3:] = b'==='
elif leftover == 4:
- return encoded[:-1] + b'='
- return encoded
-
+ encoded[-1:] = b'='
+ return bytes(encoded)
def b32decode(s, casefold=False, map01=None):
"""Decode a Base32 encoded byte string.
@@ -217,8 +195,7 @@ def b32decode(s, casefold=False, map01=None):
characters present in the input.
"""
s = _bytes_from_decode_data(s)
- quanta, leftover = divmod(len(s), 8)
- if leftover:
+ if len(s) % 8:
raise binascii.Error('Incorrect padding')
# Handle section 2.4 zero and one mapping. The flag map01 will be either
# False, or the character to map the digit 1 (one) to. It should be
@@ -232,42 +209,36 @@ def b32decode(s, casefold=False, map01=None):
# Strip off pad characters from the right. We need to count the pad
# characters because this will tell us how many null bytes to remove from
# the end of the decoded string.
- padchars = 0
- mo = re.search(b'(?P<pad>[=]*)$', s)
- if mo:
- padchars = len(mo.group('pad'))
- if padchars > 0:
- s = s[:-padchars]
+ l = len(s)
+ s = s.rstrip(b'=')
+ padchars = l - len(s)
# Now decode the full quanta
- parts = []
- acc = 0
- shift = 35
- for c in s:
- val = _b32rev.get(c)
- if val is None:
+ decoded = bytearray()
+ b32rev = _b32rev
+ for i in range(0, len(s), 8):
+ quanta = s[i: i + 8]
+ acc = 0
+ try:
+ for c in quanta:
+ acc = (acc << 5) + b32rev[c]
+ except KeyError:
raise TypeError('Non-base32 digit found')
- acc += _b32rev[c] << shift
- shift -= 5
- if shift < 0:
- parts.append(binascii.unhexlify(bytes('%010x' % acc, "ascii")))
- acc = 0
- shift = 35
+ decoded += acc.to_bytes(5, 'big')
# Process the last, partial quanta
- last = binascii.unhexlify(bytes('%010x' % acc, "ascii"))
- if padchars == 0:
- last = b'' # No characters
- elif padchars == 1:
- last = last[:-1]
- elif padchars == 3:
- last = last[:-2]
- elif padchars == 4:
- last = last[:-3]
- elif padchars == 6:
- last = last[:-4]
- else:
- raise binascii.Error('Incorrect padding')
- parts.append(last)
- return b''.join(parts)
+ if padchars:
+ acc <<= 5 * padchars
+ last = acc.to_bytes(5, 'big')
+ if padchars == 1:
+ decoded[-5:] = last[:-1]
+ elif padchars == 3:
+ decoded[-5:] = last[:-2]
+ elif padchars == 4:
+ decoded[-5:] = last[:-3]
+ elif padchars == 6:
+ decoded[-5:] = last[:-4]
+ else:
+ raise binascii.Error('Incorrect padding')
+ return bytes(decoded)