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0e5532d6cf
The signature of mbedtls_mpi_cmp_mpi_ct() meant to support using it in place of mbedtls_mpi_cmp_mpi(). This meant full comparison functionality and a signed result. To make the function more universal and friendly to constant time coding, we change the result type to unsigned. Theoretically, we could encode the comparison result in an unsigned value, but it would be less intuitive. Therefore we won't be able to represent the result as unsigned anymore and the functionality will be constrained to checking if the first operand is less than the second. This is sufficient to support the current use case and to check any relationship between MPIs. The only drawback is that we need to call the function twice when checking for equality, but this can be optimised later if an when it is needed.