codekingpro/portable-devtools

1# Copyright 2014 Google Inc. All rights reserved.2#3# Licensed under the Apache License, Version 2.0 (the "License");4# you may not use this file except in compliance with the License.5# You may obtain a copy of the License at6#7#     http://www.apache.org/licenses/LICENSE-2.08#9# Unless required by applicable law or agreed to in writing, software10# distributed under the License is distributed on an "AS IS" BASIS,11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.12# See the License for the specific language governing permissions and13# limitations under the License.14 15from . import encode16from . import number_types as N17 18 19class Table(object):20  """Table wraps a byte slice and provides read access to its data.21 22  The variable `Pos` indicates the root of the FlatBuffers object therein.23  """24 25  __slots__ = ("Bytes", "Pos")26 27  def __init__(self, buf, pos):28    N.enforce_number(pos, N.UOffsetTFlags)29 30    self.Bytes = buf31    self.Pos = pos32 33  def Offset(self, vtableOffset):34    """Offset provides access into the Table's vtable.35 36    Deprecated fields are ignored by checking the vtable's length.37    """38 39    vtable = self.Pos - self.Get(N.SOffsetTFlags, self.Pos)40    vtableEnd = self.Get(N.VOffsetTFlags, vtable)41    if vtableOffset < vtableEnd:42      return self.Get(N.VOffsetTFlags, vtable + vtableOffset)43    return 044 45  def Indirect(self, off):46    """Indirect retrieves the relative offset stored at `offset`."""47    N.enforce_number(off, N.UOffsetTFlags)48    return off + encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)49 50  def String(self, off):51    """String gets a string from data stored inside the flatbuffer."""52    N.enforce_number(off, N.UOffsetTFlags)53    off += encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)54    start = off + N.UOffsetTFlags.bytewidth55    length = encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)56    return bytes(self.Bytes[start : start + length])57 58  def VectorLen(self, off):59    """VectorLen retrieves the length of the vector whose offset is stored60 61    at "off" in this object.62    """63    N.enforce_number(off, N.UOffsetTFlags)64 65    off += self.Pos66    off += encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)67    ret = encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)68    return ret69 70  def Vector(self, off):71    """Vector retrieves the start of data of the vector whose offset is72 73    stored at "off" in this object.74    """75    N.enforce_number(off, N.UOffsetTFlags)76 77    off += self.Pos78    x = off + self.Get(N.UOffsetTFlags, off)79    # data starts after metadata containing the vector length80    x += N.UOffsetTFlags.bytewidth81    return x82 83  def Union(self, t2, off):84    """Union initializes any Table-derived type to point to the union at85 86    the given offset.87    """88    assert type(t2) is Table89    N.enforce_number(off, N.UOffsetTFlags)90 91    off += self.Pos92    t2.Pos = off + self.Get(N.UOffsetTFlags, off)93    t2.Bytes = self.Bytes94 95  def Get(self, flags, off):96    """Get retrieves a value of the type specified by `flags`  at the97 98    given offset.99    """100    N.enforce_number(off, N.UOffsetTFlags)101    return flags.py_type(encode.Get(flags.packer_type, self.Bytes, off))102 103  def GetSlot(self, slot, d, validator_flags):104    N.enforce_number(slot, N.VOffsetTFlags)105    if validator_flags is not None:106      N.enforce_number(d, validator_flags)107    off = self.Offset(slot)108    if off == 0:109      return d110    return self.Get(validator_flags, self.Pos + off)111 112  def GetVectorAsNumpy(self, flags, off):113    """GetVectorAsNumpy returns the vector that starts at `Vector(off)`114 115    as a numpy array with the type specified by `flags`. The array is116    a `view` into Bytes, so modifying the returned array will117    modify Bytes in place.118    """119    offset = self.Vector(off)120    length = self.VectorLen(off)  # TODO: length accounts for bytewidth, right?121    numpy_dtype = N.to_numpy_type(flags)122    return encode.GetVectorAsNumpy(numpy_dtype, self.Bytes, length, offset)123 124  def GetArrayAsNumpy(self, flags, off, length):125    """GetArrayAsNumpy returns the array with fixed width that starts at `Vector(offset)`126 127    with length `length` as a numpy array with the type specified by `flags`.128    The129    array is a `view` into Bytes so modifying the returned will modify Bytes in130    place.131    """132    numpy_dtype = N.to_numpy_type(flags)133    return encode.GetVectorAsNumpy(numpy_dtype, self.Bytes, length, off)134 135  def GetVOffsetTSlot(self, slot, d):136    """GetVOffsetTSlot retrieves the VOffsetT that the given vtable location137 138    points to. If the vtable value is zero, the default value `d`139    will be returned.140    """141 142    N.enforce_number(slot, N.VOffsetTFlags)143    N.enforce_number(d, N.VOffsetTFlags)144 145    off = self.Offset(slot)146    if off == 0:147      return d148    return off149