Fix special case testing signbit on NaNs

Author: honno

array_api_tests/test_special_cases.py

@@ -19,7 +19,7 @@
 from dataclasses import dataclass, field
 from decimal import ROUND_HALF_EVEN, Decimal
 from enum import Enum, auto
-from typing import Any, Callable, Dict, List, Optional, Protocol, Tuple
+from typing import Any, Callable, Dict, List, Optional, Protocol, Tuple, Literal
 from warnings import warn
 
 import pytest
@@ -544,6 +544,10 @@ class UnaryCase(Case):
     "If two integers are equally close to ``x_i``, "
     "the result is the even integer closest to ``x_i``"
 )
+r_nan_signbit = re.compile(
+    "If ``x_i`` is ``NaN`` and the sign bit of ``x_i`` is ``(.+)``, "
+    "the result is ``(.+)``"
+)
 
 
 def integers_from_dtype(dtype: DataType, **kw) -> st.SearchStrategy[float]:
@@ -599,6 +603,25 @@ def trailing_halves_from_dtype(dtype: DataType) -> st.SearchStrategy[float]:
 )
 
 
+def make_nan_signbit_case(signbit: Literal[0, 1], expected: bool) -> UnaryCase:
+    if signbit:
+        sign = -1
+        nan_expr = "-NaN"
+        float_arg = "-nan"
+    else:
+        sign = 1
+        nan_expr = "+NaN"
+        float_arg = "nan"
+
+    return UnaryCase(
+        cond_expr=f"x_i is {nan_expr}",
+        cond=lambda i: math.isnan(i) and math.copysign(1, i) == sign,
+        cond_from_dtype=lambda _: st.just(float(float_arg)),
+        result_expr=str(expected),
+        check_result=lambda _, result: result == float(expected),
+    )
+
+
 def make_unary_check_result(check_just_result: UnaryCheck) -> UnaryResultCheck:
     def check_result(i: float, result: float) -> bool:
         return check_just_result(result)
@@ -655,10 +678,14 @@ def parse_unary_case_block(case_block: str) -> List[UnaryCase]:
     cases = []
     for case_m in r_case.finditer(case_block):
         case_str = case_m.group(1)
-        if m := r_already_int_case.search(case_str):
+        if r_already_int_case.search(case_str):
             cases.append(already_int_case)
-        elif m := r_even_round_halves_case.search(case_str):
+        elif r_even_round_halves_case.search(case_str):
             cases.append(even_round_halves_case)
+        elif m := r_nan_signbit.search(case_str):
+            signbit = parse_value(m.group(1))
+            expected = bool(parse_value(m.group(2)))
+            cases.append(make_nan_signbit_case(signbit, expected))
         elif m := r_unary_case.search(case_str):
             try:
                 cond, cond_expr_template, cond_from_dtype = parse_cond(m.group(1))