Provide a way to override iteration count

Benchmarks need a way to limit how many iterations get run. Introuce a
way to inject this information here.

Author: tgross35

crates/libm-test/src/run_cfg.rs

@@ -40,6 +40,8 @@ pub struct CheckCtx {
     /// Source of truth for tests.
     pub basis: CheckBasis,
     pub gen_kind: GeneratorKind,
+    /// If specified, this value will override the value returned by [`iteration_count`].
+    pub override_iterations: Option<u64>,
 }
 
 impl CheckCtx {
@@ -53,6 +55,7 @@ impl CheckCtx {
             base_name_str: fn_ident.base_name().as_str(),
             basis,
             gen_kind,
+            override_iterations: None,
         };
         ret.ulp = crate::default_ulp(&ret);
         ret
@@ -62,6 +65,10 @@ impl CheckCtx {
     pub fn input_count(&self) -> usize {
         self.fn_ident.math_op().rust_sig.args.len()
     }
+
+    pub fn override_iterations(&mut self, count: u64) {
+        self.override_iterations = Some(count)
+    }
 }
 
 /// Possible items to test against
@@ -71,6 +78,8 @@ pub enum CheckBasis {
     Musl,
     /// Check against infinite precision (MPFR).
     Mpfr,
+    /// Benchmarks or other times when this is not relevant.
+    None,
 }
 
 /// The different kinds of generators that provide test input, which account for input pattern
@@ -216,13 +225,20 @@ pub fn iteration_count(ctx: &CheckCtx, argnum: usize) -> u64 {
         total_iterations = 800;
     }
 
+    let mut overridden = false;
+    if let Some(count) = ctx.override_iterations {
+        total_iterations = count;
+        overridden = true;
+    }
+
     // Adjust for the number of inputs
     let ntests = match t_env.input_count {
         1 => total_iterations,
         2 => (total_iterations as f64).sqrt().ceil() as u64,
         3 => (total_iterations as f64).cbrt().ceil() as u64,
         _ => panic!("test has more than three arguments"),
     };
+
     let total = ntests.pow(t_env.input_count.try_into().unwrap());
 
     let seed_msg = match ctx.gen_kind {
@@ -235,12 +251,13 @@ pub fn iteration_count(ctx: &CheckCtx, argnum: usize) -> u64 {
 
     test_log(&format!(
         "{gen_kind:?} {basis:?} {fn_ident} arg {arg}/{args}: {ntests} iterations \
-         ({total} total){seed_msg}",
+         ({total} total){seed_msg}{omsg}",
         gen_kind = ctx.gen_kind,
         basis = ctx.basis,
         fn_ident = ctx.fn_ident,
         arg = argnum + 1,
         args = t_env.input_count,
+        omsg = if overridden { " (overridden)" } else { "" }
     ));
 
     ntests