[GitHub] kamaci commented on issue #6932: Raw byte values should not be used in bitwise operations in combination with shifts.

[GitBox <gi...@apache.org>]

kamaci commented on issue #6932: Raw byte values should not be used in bitwise operations in combination with shifts.
URL: https://github.com/apache/incubator-druid/pull/6932#issuecomment-459274669
 
 
   Here are some explanations about this vulnerability:
   
   > When reading bytes in order to build other primitive values such as ints or longs, the byte values are automatically promoted, but that promotion can have unexpected results.
   > 
   > For instance, the binary representation of the integer 640 is 0b0000_0010_1000_0000, which can also be written with the array of (unsigned) bytes [2, 128]. However, since Java uses two's complement, the representation of the integer in signed bytes will be [2, -128] (because the byte 0b1000_0000 is promoted to the int 0b1111_1111_1111_1111_1111_1111_1000_0000). Consequently, trying to reconstruct the initial integer by shifting and adding the values of the bytes without taking care of the sign will not produce the expected result.
   
   https://wiki.sei.cmu.edu/confluence/display/java/NUM52-J.+Be+aware+of+numeric+promotion+behavior

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