def __init__(self, **kwargs):
buffer = kwargs.get("buffer", None)
self.flags = kwargs.get("flags", b'\x00')
self.pageCapacity = kwargs.get("pageCapacity", len(buffer))
self.tupleSize = kwargs.get("tupleSize", None)
self.bitmap = kwargs.get("bitmap", None)
if buffer == None:
raise ValueError(
"No backing buffer supplied for SlottedPageHeader")
if self.bitmap == None:
headerSizeWithoutBitmap = struct.Struct("cHHH").size
tupleCapacity = math.floor(
(8 * (self.pageCapacity - headerSizeWithoutBitmap)) /
(1 + (8 * self.tupleSize)))
bString = '0b' + ('0' * tupleCapacity)
self.bitmap = BitArray(bString)
self.binrepr = struct.Struct("cHHH" +
str(math.ceil(len(self.bitmap))) + 's')
self.size = self.binrepr.size
self.freeSpaceOffset = self.size
buffer[0:self.size] = self.pack()
def unpack(cls, buffer):
binrepr1 = struct.Struct("cHHH")
values1 = binrepr1.unpack_from(buffer)
headerSizeWithoutBitmap = binrepr1.size
tupleCapacity = math.floor(
(8 * (values1[3] - headerSizeWithoutBitmap)) / (1 +
(8 * values1[1])))
binrepr2 = struct.Struct("cHHH" + str(math.ceil(tupleCapacity)) + 's')
values2 = binrepr2.unpack_from(buffer)
bString = '0b' + ('0' * tupleCapacity)
bitmap = BitArray(bString)
index = 0
for bit in values2[4]:
if index >= tupleCapacity:
break
if bit:
bitmap[index] = '0b1'
else:
bitmap[index] = '0b0'
index = index + 1
if len(values2) == 5:
return cls(buffer=buffer,
flags=values2[0],
tupleSize=values2[1],
freeSpaceOffset=values2[2],
pageCapacity=values2[3],
bitmap=bitmap)
