bitfield.py

来自「这是一个嵌入式linux系统下的命令工具包」· Python 代码 · 共 163 行

# Written by Bram Cohen, Uoti Urpala, and John Hoffman
# see LICENSE.txt for license information

try:
    True
except:
    True = 1
    False = 0
    bool = lambda x: not not x

try:
    sum([1])
    negsum = lambda a: len(a)-sum(a)
except:
    negsum = lambda a: reduce(lambda x,y: x+(not y), a, 0)
    
def _int_to_booleans(x):
    r = []
    for i in range(8):
        r.append(bool(x & 0x80))
        x <<= 1
    return tuple(r)

lookup_table = []
reverse_lookup_table = {}
for i in xrange(256):
    x = _int_to_booleans(i)
    lookup_table.append(x)
    reverse_lookup_table[x] = chr(i)


class Bitfield:
    def __init__(self, length = None, bitstring = None, copyfrom = None):
        if copyfrom is not None:
            self.length = copyfrom.length
            self.array = copyfrom.array[:]
            self.numfalse = copyfrom.numfalse
            return
        if length is None:
            raise ValueError, "length must be provided unless copying from another array"
        self.length = length
        if bitstring is not None:
            extra = len(bitstring) * 8 - length
            if extra < 0 or extra >= 8:
                raise ValueError
            t = lookup_table
            r = []
            for c in bitstring:
                r.extend(t[ord(c)])
            if extra > 0:
                if r[-extra:] != [0] * extra:
                    raise ValueError
                del r[-extra:]
            self.array = r
            self.numfalse = negsum(r)
        else:
            self.array = [False] * length
            self.numfalse = length

    def __setitem__(self, index, val):
        val = bool(val)
        self.numfalse += self.array[index]-val
        self.array[index] = val

    def __getitem__(self, index):
        return self.array[index]

    def __len__(self):
        return self.length

    def tostring(self):
        booleans = self.array
        t = reverse_lookup_table
        s = len(booleans) % 8
        r = [ t[tuple(booleans[x:x+8])] for x in xrange(0, len(booleans)-s, 8) ]
        if s:
            r += t[tuple(booleans[-s:] + ([0] * (8-s)))]
        return ''.join(r)

    def complete(self):
        return not self.numfalse


def test_bitfield():
    try:
        x = Bitfield(7, 'ab')
        assert False
    except ValueError:
        pass
    try:
        x = Bitfield(7, 'ab')
        assert False
    except ValueError:
        pass
    try:
        x = Bitfield(9, 'abc')
        assert False
    except ValueError:
        pass
    try:
        x = Bitfield(0, 'a')
        assert False
    except ValueError:
        pass
    try:
        x = Bitfield(1, '')
        assert False
    except ValueError:
        pass
    try:
        x = Bitfield(7, '')
        assert False
    except ValueError:
        pass
    try:
        x = Bitfield(8, '')
        assert False
    except ValueError:
        pass
    try:
        x = Bitfield(9, 'a')
        assert False
    except ValueError:
        pass
    try:
        x = Bitfield(7, chr(1))
        assert False
    except ValueError:
        pass
    try:
        x = Bitfield(9, chr(0) + chr(0x40))
        assert False
    except ValueError:
        pass
    assert Bitfield(0, '').tostring() == ''
    assert Bitfield(1, chr(0x80)).tostring() == chr(0x80)
    assert Bitfield(7, chr(0x02)).tostring() == chr(0x02)
    assert Bitfield(8, chr(0xFF)).tostring() == chr(0xFF)
    assert Bitfield(9, chr(0) + chr(0x80)).tostring() == chr(0) + chr(0x80)
    x = Bitfield(1)
    assert x.numfalse == 1
    x[0] = 1
    assert x.numfalse == 0
    x[0] = 1
    assert x.numfalse == 0
    assert x.tostring() == chr(0x80)
    x = Bitfield(7)
    assert len(x) == 7
    x[6] = 1
    assert x.numfalse == 6
    assert x.tostring() == chr(0x02)
    x = Bitfield(8)
    x[7] = 1
    assert x.tostring() == chr(1)
    x = Bitfield(9)
    x[8] = 1
    assert x.numfalse == 8
    assert x.tostring() == chr(0) + chr(0x80)
    x = Bitfield(8, chr(0xC4))
    assert len(x) == 8
    assert x.numfalse == 5
    assert x.tostring() == chr(0xC4)