MPC: modulo not working as expected

[sebw42]

Hi, the MPC compiler on the mpc_aws branch seems to have an issue with the modulo operation.
Here is an example:

int main() {
    return (0-1) % 10;
}

This returns 5.

It works as expected when using a secret input instead of 0-1:

int main(__attribute__(private(0)) int x) {
    return x % 10;
}

Compilation command:

export CARGO_MANIFEST_DIR="$PWD"; ./target/release/examples/circ --parties 2 examples/C/mpc/program.c mpc --cost-model "empirical" --selection-scheme css

Execution command:

/path/to/ABY/build/bin/aby_interpreter -m mpc -f ./scripts/aby_tests/tests/program_c -t ./scripts/aby_tests/test_inputs/program.txt -r 0 & /path/to/ABY/build/bin/aby_interpreter -m mpc -f ./scripts/aby_tests/tests/program_c -t ./scripts/aby_tests/test_inputs/program.txt -r 1

Thanks for looking into this!