Function execarith 

pub fn execarith(state: &mut estate, _do_exec: i32) -> i32

Port of execarith() from Src/exec.c:5235 — C decl execarith(Estate state, UNUSED(int do_exec)). Run a (( ... )) arithmetic command; returns 0 when val != 0 (success), 1 when val == 0 (false), 2 on parse error.