decoder.py 文件源码

def valueDecoder(self, fullSubstrate, substrate, asn1Spec, tagSet,
                     length, state, decodeFun, substrateFun):
        head, tail = substrate[:length], substrate[length:]
        if not head:
            return self._createComponent(asn1Spec, tagSet, 0.0), tail
        fo = oct2int(head[0]); head = head[1:]
        if fo & 0x80:  # binary enoding
            n = (fo & 0x03) + 1
            if n == 4:
                n = oct2int(head[0])
            eo, head = head[:n], head[n:]
            if not eo or not head:
                raise error.PyAsn1Error('Real exponent screwed')
            e = oct2int(eo[0]) & 0x80 and -1 or 0
            while eo:         # exponent
                e <<= 8
                e |= oct2int(eo[0])
                eo = eo[1:]
            p = 0
            while head:  # value
                p <<= 8
                p |= oct2int(head[0])
                head = head[1:]
            if fo & 0x40:    # sign bit
                p = -p
            value = (p, 2, e)
        elif fo & 0x40:  # infinite value
            value = fo & 0x01 and '-inf' or 'inf'
        elif fo & 0xc0 == 0:  # character encoding
            try:
                if fo & 0x3 == 0x1:  # NR1
                    value = (int(head), 10, 0)
                elif fo & 0x3 == 0x2:  # NR2
                    value = float(head)
                elif fo & 0x3 == 0x3:  # NR3
                    value = float(head)
                else:
                    raise error.SubstrateUnderrunError(
                        'Unknown NR (tag %s)' % fo
                        )
            except ValueError:
                raise error.SubstrateUnderrunError(
                    'Bad character Real syntax'
                    )
        else:
            raise error.SubstrateUnderrunError(
                'Unknown encoding (tag %s)' % fo
                )
        return self._createComponent(asn1Spec, tagSet, value), tail