From f028611faf62a9b87430ff782ab0bb91d5c63a8f Mon Sep 17 00:00:00 2001
From: Trevor Gross <tmgross@umich.edu>
Date: Fri, 7 Feb 2025 01:05:38 +0000
Subject: [PATCH] Check more subnormal values during edge cases tests

Add checks at the max subnormal value and a couple values scatted
throughout the subnormal range. This helped identifiy a bug in
`fmaf128`.

As part of this, slightly reduce the amount of edge cases checked
without optimizations because the change makes it become noticible.
---
 .../crates/libm-test/src/gen/edge_cases.rs    | 20 ++++++++++++++++++-
 .../libm/crates/libm-test/src/run_cfg.rs      |  2 +-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/library/compiler-builtins/libm/crates/libm-test/src/gen/edge_cases.rs b/library/compiler-builtins/libm/crates/libm-test/src/gen/edge_cases.rs
index 8da635114d2f..69b59a105674 100644
--- a/library/compiler-builtins/libm/crates/libm-test/src/gen/edge_cases.rs
+++ b/library/compiler-builtins/libm/crates/libm-test/src/gen/edge_cases.rs
@@ -1,9 +1,10 @@
 //! A generator that checks a handful of cases near infinities, zeros, asymptotes, and NaNs.
 
-use libm::support::{CastInto, Float, Int};
+use libm::support::{CastInto, Float, Int, MinInt};
 
 use crate::domain::get_domain;
 use crate::gen::KnownSize;
+use crate::op::OpITy;
 use crate::run_cfg::{check_near_count, check_point_count};
 use crate::{BaseName, CheckCtx, FloatExt, FloatTy, MathOp, test_log};
 
@@ -21,6 +22,7 @@ where
     Op: MathOp,
 {
     let mut ret = Vec::new();
+    let one = OpITy::<Op>::ONE;
     let values = &mut ret;
     let domain = get_domain::<_, i8>(ctx.fn_ident, argnum).unwrap_float();
     let domain_start = domain.range_start();
@@ -51,6 +53,22 @@ where
     values.push(Op::FTy::NAN);
     values.extend(Op::FTy::consts().iter());
 
+    // Check around the maximum subnormal value
+    let sub_max = Op::FTy::from_bits(Op::FTy::SIG_MASK);
+    count_up(sub_max, near_points, values);
+    count_down(sub_max, near_points, values);
+    count_up(-sub_max, near_points, values);
+    count_down(-sub_max, near_points, values);
+
+    // Check a few values around the subnormal range
+    for shift in (0..Op::FTy::SIG_BITS).step_by(Op::FTy::SIG_BITS as usize / 5) {
+        let v = Op::FTy::from_bits(one << shift);
+        count_up(v, 2, values);
+        count_down(v, 2, values);
+        count_up(-v, 2, values);
+        count_down(-v, 2, values);
+    }
+
     // Check around asymptotes
     if let Some(f) = domain.check_points {
         let iter = f();
diff --git a/library/compiler-builtins/libm/crates/libm-test/src/run_cfg.rs b/library/compiler-builtins/libm/crates/libm-test/src/run_cfg.rs
index 5728c3b2e5b0..4dd43bdf3868 100644
--- a/library/compiler-builtins/libm/crates/libm-test/src/run_cfg.rs
+++ b/library/compiler-builtins/libm/crates/libm-test/src/run_cfg.rs
@@ -342,7 +342,7 @@ pub fn check_near_count(ctx: &CheckCtx) -> u64 {
             x => panic!("unexpected argument count {x}"),
         }
     } else {
-        10
+        8
     }
 }