def _StructPackDecoder(wire_type, format):
"""Return a constructor for a decoder for a fixed-width field.
Args:
wire_type: The field's wire type.
format: The format string to pass to struct.unpack().
"""
value_size = struct.calcsize(format)
local_unpack = struct.unpack
# Reusing _SimpleDecoder is slightly slower than copying a bunch of code, but
# not enough to make a significant difference.
# Note that we expect someone up-stack to catch struct.error and convert
# it to _DecodeError -- this way we don't have to set up exception-
# handling blocks every time we parse one value.
def InnerDecode(buffer, pos):
new_pos = pos + value_size
result = local_unpack(format, buffer[pos:new_pos])[0]
return (result, new_pos)
return _SimpleDecoder(wire_type, InnerDecode)
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