rdblue commented on code in PR #4920: URL: https://github.com/apache/iceberg/pull/4920#discussion_r895224444
########## python/src/iceberg/avro/decoder.py: ########## @@ -0,0 +1,193 @@ +# Licensed to the Apache Software Foundation (ASF) under one +# or more contributor license agreements. See the NOTICE file +# distributed with this work for additional information +# regarding copyright ownership. The ASF licenses this file +# to you under the Apache License, Version 2.0 (the +# "License"); you may not use this file except in compliance +# with the License. You may obtain a copy of the License at +# +# http://www.apache.org/licenses/LICENSE-2.0 +# +# Unless required by applicable law or agreed to in writing, +# software distributed under the License is distributed on an +# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +# KIND, either express or implied. See the License for the +# specific language governing permissions and limitations +# under the License. +import datetime +import decimal +import struct + +from iceberg.io.base import InputStream + +STRUCT_FLOAT = struct.Struct("<f") # little-endian float +STRUCT_DOUBLE = struct.Struct("<d") # little-endian double +STRUCT_SIGNED_SHORT = struct.Struct(">h") # big-endian signed short +STRUCT_SIGNED_INT = struct.Struct(">i") # big-endian signed int +STRUCT_SIGNED_LONG = struct.Struct(">q") # big-endian signed long + + +class BinaryDecoder: + """Read leaf values.""" + + _input_stream: InputStream + + def __init__(self, input_stream: InputStream) -> None: + """ + reader is a Python object on which we can call read, seek, and tell. + """ + self._input_stream = input_stream + + def read(self, n: int) -> bytes: + """ + Read n bytes. + """ + if n < 0: + raise ValueError(f"Requested {n} bytes to read, expected positive integer.") + read_bytes = self._input_stream.read(n) + if len(read_bytes) != n: + raise ValueError(f"Read {len(read_bytes)} bytes, expected {n} bytes") + return read_bytes + + def read_boolean(self) -> bool: + """ + a boolean is written as a single byte + whose value is either 0 (false) or 1 (true). + """ + return ord(self.read(1)) == 1 + + def read_int(self) -> int: + """int values are written using variable-length, zigzag coding.""" + return self.read_long() + + def read_long(self) -> int: + """long values are written using variable-length, zigzag coding.""" + b = ord(self.read(1)) + n = b & 0x7F + shift = 7 + while (b & 0x80) != 0: + b = ord(self.read(1)) + n |= (b & 0x7F) << shift + shift += 7 + datum = (n >> 1) ^ -(n & 1) + return datum + + def read_float(self) -> float: + """ + A float is written as 4 bytes. + The float is converted into a 32-bit integer using a method equivalent to + Java's floatToIntBits and then encoded in little-endian format. + """ + return float(STRUCT_FLOAT.unpack(self.read(4))[0]) + + def read_double(self) -> float: + """ + A double is written as 8 bytes. + The double is converted into a 64-bit integer using a method equivalent to + Java's doubleToLongBits and then encoded in little-endian format. + """ + return float(STRUCT_DOUBLE.unpack(self.read(8))[0]) + + def read_decimal_from_bytes(self, precision: int, scale: int) -> decimal.Decimal: + """ + Decimal bytes are decoded as signed short, int or long depending on the + size of bytes. + """ + size = self.read_long() + return self.read_decimal_from_fixed(precision, scale, size) + + def read_decimal_from_fixed(self, precision: int, scale: int, size: int) -> decimal.Decimal: + """ + Decimal is encoded as fixed. Fixed instances are encoded using the + number of bytes declared in the schema. + """ + datum = self.read(size) + unscaled_datum = 0 + msb = struct.unpack("!b", datum[0:1])[0] + leftmost_bit = (msb >> 7) & 1 Review Comment: @Fokko, do you know why this uses `ord` and `unpack`? I don't think it needs to be this complicated. If you access a byte, then it is returned as the unsigned value. ```python datum = b'\x01\x02\x03\xFF' datum[0] # => 1 datum[-1] # => 255 ``` Maybe I'm missing something, but I don't see how the line to produce `msb` isn't equivalent to `datum[0]`. I think this could be: ```java unscaled_datum = 0 if datum[0] & 0x80 != 0: # negative two's complement ... else: # positive ... ``` -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
