binascii: Add Python base64 implementation from PyPy3-2.4.0's interp_base64.py

Full source path in tarball:
pypy3-2.4.0-src/pypy/module/binascii/interp_base64.py

binascii/binascii.py

@@ -1,5 +1,113 @@
-def b2a_base64():
-    raise NotImplementError
+from pypy.interpreter.error import OperationError
+from pypy.interpreter.gateway import unwrap_spec
+from rpython.rlib.rstring import StringBuilder
+from pypy.module.binascii.interp_binascii import raise_Error
+from rpython.rlib.rarithmetic import ovfcheck
 
-def a2b_base64():
-    raise NotImplementError
+# ____________________________________________________________
+
+PAD = '='
+
+table_a2b_base64 = [
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,62, -1,-1,-1,63,
+    52,53,54,55, 56,57,58,59, 60,61,-1,-1, -1,-1,-1,-1, # Note PAD->-1 here
+    -1, 0, 1, 2,  3, 4, 5, 6,  7, 8, 9,10, 11,12,13,14,
+    15,16,17,18, 19,20,21,22, 23,24,25,-1, -1,-1,-1,-1,
+    -1,26,27,28, 29,30,31,32, 33,34,35,36, 37,38,39,40,
+    41,42,43,44, 45,46,47,48, 49,50,51,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
+    -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,    
+]
+def _transform(n):
+    if n == -1:
+        return '\xff'
+    else:
+        return chr(n)
+table_a2b_base64 = ''.join(map(_transform, table_a2b_base64))
+assert len(table_a2b_base64) == 256
+
+
+@unwrap_spec(ascii='bufferstr')
+def a2b_base64(space, ascii):
+    "Decode a line of base64 data."
+
+    res = StringBuilder((len(ascii) // 4) * 3)   # maximum estimate
+    quad_pos = 0
+    leftchar = 0
+    leftbits = 0
+    last_char_was_a_pad = False
+
+    for c in ascii:
+        if c == PAD:
+            if quad_pos > 2 or (quad_pos == 2 and last_char_was_a_pad):
+                break      # stop on 'xxx=' or on 'xx=='
+            last_char_was_a_pad = True
+        else:
+            n = ord(table_a2b_base64[ord(c)])
+            if n == 0xff:
+                continue    # ignore strange characters
+            #
+            # Shift it in on the low end, and see if there's
+            # a byte ready for output.
+            quad_pos = (quad_pos + 1) & 3
+            leftchar = (leftchar << 6) | n
+            leftbits += 6
+            #
+            if leftbits >= 8:
+                leftbits -= 8
+                res.append(chr(leftchar >> leftbits))
+                leftchar &= ((1 << leftbits) - 1)
+            #
+            last_char_was_a_pad = False
+    else:
+        if leftbits != 0:
+            raise_Error(space, "Incorrect padding")
+
+    return space.wrapbytes(res.build())
+
+# ____________________________________________________________
+
+table_b2a_base64 = (
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")
+
+@unwrap_spec(bin='bufferstr')
+def b2a_base64(space, bin):
+    "Base64-code line of data."
+
+    newlength = (len(bin) + 2) // 3
+    try:
+        newlength = ovfcheck(newlength * 4)
+    except OverflowError:
+        raise OperationError(space.w_MemoryError, space.w_None)
+    newlength += 1
+    res = StringBuilder(newlength)
+
+    leftchar = 0
+    leftbits = 0
+    for c in bin:
+        # Shift into our buffer, and output any 6bits ready
+        leftchar = (leftchar << 8) | ord(c)
+        leftbits += 8
+        res.append(table_b2a_base64[(leftchar >> (leftbits-6)) & 0x3f])
+        leftbits -= 6
+        if leftbits >= 6:
+            res.append(table_b2a_base64[(leftchar >> (leftbits-6)) & 0x3f])
+            leftbits -= 6
+    #
+    if leftbits == 2:
+        res.append(table_b2a_base64[(leftchar & 3) << 4])
+        res.append(PAD)
+        res.append(PAD)
+    elif leftbits == 4:
+        res.append(table_b2a_base64[(leftchar & 0xf) << 2])
+        res.append(PAD)
+    res.append('\n')
+    return space.wrapbytes(res.build())