Add verbal specification and runtime-checking for fqmul()
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Signed-off-by: Hanno Becker <[email protected]>
We already have `mlkem_debug_check_bounds()` to check bounds on all elements of an array. In preparation for use in `fqmul()`, this commit adds generic `mlkem_debug_assert()` and `ASSERT()` to checking assertions, and a wrapper assertion `SCALAR_BOUND` to assert absolute bounds on scalars. Signed-off-by: Hanno Becker <[email protected]>
For bounds reasoning, we need to know that `fqmul()` is always called with a signed canonical value in one of its arguments. To simplify the spec, this commit reorders arguments to `fqmul()` so that the signed canonical twiddle is always the _second_ argument. It checks this through a debug-only assertion, and also adds a debug-assertion that the return value of `fqmul()` is always of absolute value < MLKEM_Q. Signed-off-by: Hanno Becker <[email protected]>
`mlkem_debug_check_bounds()` and its wrapper macros `BOUNDS()` etc. are working with _exclusive_ bounds, but the documentation for `mlkem_debug_check_bounds()` wrongly stated that its bounds arguments would be inclusive. This commit fixes the documentation of `mlkem_debug_check_bounds()` to say that bounds are exclusive. No change to the code is needed: We only work with the wrapper macros, and those were already documented and used with exclusive bounds. Signed-off-by: Hanno Becker <[email protected]>
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This is a preparatory PR for CBMC proofs. It reorders arguments to
fqmul()so that the signed canonical twiddle is always in the second position, says as much in the textual description offqmul(), and adds runtime assertions checking the input and output bounds during runtime (for debug builds).