This repo contains the Annotated and unannotated version of code which force a file’s CRC to any value i.e. on https://www.nayuki.io/page/forcing-a-files-crc-to-any-value
To compile from terminal, following command needs to be passed :
javac -processor signedness forcecrc32.java
In this case study I learnt that signedness checker is weak in some classes and needs enhancements such as:-
1.)java.lang.Integer- reverse function
3.)java.io.RandomAccessFile
and I think many more in the future too.
When you will compile this file using signedness checker these errors will come-
java:102: error: [comparison.unsignedlhs] comparison has an unsigned LHS
if (offset + 4 > raf.length())
^
java:114: error: [operation.mixed.unsignedrhs] MINUS operation on signed LHS and unsigned RHS values
delta = (int)multiplyMod(reciprocalMod(powMod(2, (raf.length() - offset) * 8)), delta & 0xFFFFFFFFL);
^
java:114: error: [argument.type.incompatible] incompatible types in argument.
delta = (int)multiplyMod(reciprocalMod(powMod(2, (raf.length() - offset) * 8)), delta & 0xFFFFFFFFL);
^
found : @UnknownSignedness long
required: @Unsigned long
java:118: error: [argument.type.incompatible] incompatible types in argument.
raf.seek(offset);
^
found : @Unsigned long
required: @Signed long
java:123: error: [argument.type.incompatible] incompatible types in argument.
raf.readFully(bytes4);
^
found : @Unsigned byte @UnknownSignedness []
required: @Signed byte @UnknownSignedness []
java:128: error: [argument.type.incompatible] incompatible types in argument.
raf.seek(offset);
^
found : @Unsigned long
required: @Signed long
These errors shows the weakness in signedness checker.
Due to this errors came and in someplaces I had to @SuppressWarnings. I would not have found these problems in signedness checker without doing this case study. Will further analyze this checker where it needs more enhancements.
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