From 584982b2511d763da96cdbce8a0e5f97083ca527 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Sun, 18 Oct 2026 11:36:05 +0000
Subject: [PATCH 1/2] Initial plan


From 76cdf5ceb740d1fe6d90b5006a31f614921e6ad7 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Sun, 18 Oct 2026 11:38:10 +0000
Subject: [PATCH 2/2] Fix TiesToAway rounding just below subnormal midpoint

Co-authored-by: awf <128119+awf@users.noreply.github.com>
---
 src/gfloat/round.py          |  2 +-
 test/test_round_underflow.py | 21 +++++++++++++++++++--
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/gfloat/round.py b/src/gfloat/round.py
index 32be3a8..4967f7d 100644
--- a/src/gfloat/round.py
+++ b/src/gfloat/round.py
@@ -137,7 +137,7 @@ def round_float(
             case RoundMode.TowardNegative:
                 should_round_away = sign and delta > 0
             case RoundMode.TiesToAway:
-                should_round_away = delta + 0.5 >= 1.0
+                should_round_away = delta >= 0.5
             case RoundMode.TiesToEven:
                 should_round_away = delta > 0.5 or (delta == 0.5 and code_is_odd)
             case RoundMode.ToOdd:
diff --git a/test/test_round_underflow.py b/test/test_round_underflow.py
index 1c6194e..0c0ae5e 100644
--- a/test/test_round_underflow.py
+++ b/test/test_round_underflow.py
@@ -2,12 +2,14 @@
 
 from typing import Callable
 
+import math
+
 import numpy as np
 import pytest
 
-from gfloat import FormatInfo, RoundMode, decode_float, encode_float
+from gfloat import FormatInfo, RoundMode, Signedness, decode_float, encode_float
 from gfloat import round_float, round_ndarray
-from gfloat.formats import Domain, format_info_ocp_e8m0
+from gfloat.formats import Domain, format_info_ocp_e8m0, format_info_p3109
 
 
 def scalar_round(
@@ -41,6 +43,21 @@ def no_subnormal_format(precision: int, signed: bool = False) -> FormatInfo:
     )
 
 
+@pytest.mark.parametrize("rounder", [scalar_round, array_round])
+@pytest.mark.parametrize("sign", [1, -1])
+@pytest.mark.parametrize("direction", [0.0, 0.5, 1.0])
+def test_round_ties_to_away_subnormal_midpoint(
+    rounder: Callable, sign: int, direction: float
+) -> None:
+    fi = format_info_p3109(8, 3, Signedness.Signed, Domain.Extended)
+    midpoint = fi.smallest / 2
+    value = math.nextafter(midpoint, direction * fi.smallest)
+    expected = 0.0 if direction == 0.0 else sign * fi.smallest
+    actual = rounder(fi, sign * value, RoundMode.TiesToAway, False, 0)
+    assert actual == expected
+    assert np.signbit(actual) == np.signbit(expected)
+
+
 @pytest.mark.parametrize("rounder", [scalar_round, array_round])
 @pytest.mark.parametrize("rnd", RoundMode)
 @pytest.mark.parametrize("sat", [False, True])