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Code Assertion


This statement introduces conditions to be checked. Here, we distinguish two cases depending on if bool_expression is unknown at compilation time:

  • If the assert statement depends on a control flow with only known conditions (see Unknowns) and the bool_expression is known (e.g., if it only depends on the value of template parameters or field constants), the assert is evaluated in compilation time. If the result of the evaluation is false, then the compilation fails. Consider the next piece of code:
template A(n) {
  signal input in;
  in * in === n;

component main = A(0);

Here, the assert can be evaluated during the compilation and the result of the evaluation is false. Thus, the compilation ends throwing error error[T3001]: False assert reached. If the main component was defined as component main = A(2);, then the compilation correctly finishes.

  • Otherwise, the compiler adds an assert in the final witness-generation code that must be satisfied during the witness generation. In the next example, if the input in passed as parameter to produce the witness does not satisfy the assert, then the witness will not be generated.
template Translate(n) {
  signal input in;  
  . . .

Recall that, when a constraint like in * in === n; is introduced with ===, then an assert is automatically added in the witness generation code. In this case, assert(in * in == n).