WIP,TST: Add exhaustive test for FPEs in casts

unfortunately, I had to realize that float -> integer casts are not
well defined when values are out of range for the integer.
This is a problem with C, but means that neither the warnings seem
to be particularly well defined...
(I suspect, on my CPU it either warns OR gives "valid" integer overflow
results, but the question is if that is even universally true...)

1 files changed, 135 insertions, 0 deletions

diff --git a/numpy/core/tests/test_casting_floatingpoint_errors.py b/numpy/core/tests/test_casting_floatingpoint_errors.py
new file mode 100644
index 000000000..797dc3387
--- /dev/null
+++ b/numpy/core/tests/test_casting_floatingpoint_errors.py
@@ -0,0 +1,135 @@
+import pytest
+from pytest import param
+
+import numpy as np
+
+
+def values_and_dtypes():
+    """
+    Generate value+dtype pairs that generate floating point errors during
+    casts.  The invalid casts to integers will generate "invalid" value
+    warnings, the float casts all generate "overflow".
+
+    (The Python int/float paths don't need to get tested in all the same
+    situations, but it does not hurt.)
+    """
+    # Casting to float16:
+    yield param(70000, "float16", id="int-to-f2")
+    yield param("70000", "float16", id="str-to-f2")
+    yield param(70000.0, "float16", id="float-to-f2")
+    yield param(np.longdouble(70000.), "float16", id="longdouble-to-f2")
+    yield param(np.float64(70000.), "float16", id="double-to-f2")
+    yield param(np.float32(70000.), "float16", id="float-to-f2")
+    # Casting to float32:
+    yield param(10**100, "float32", id="int-to-f4")
+    yield param(1e100, "float32", id="float-to-f2")
+    yield param(np.longdouble(1e300), "float32", id="longdouble-to-f2")
+    yield param(np.float64(1e300), "float32", id="double-to-f2")
+    # Casting to float64:
+    if np.finfo(np.longdouble).max > np.finfo(np.float64).max:
+        yield param(np.finfo(np.longdouble).max, "float64",
+                    id="longdouble-to-f4")
+
+    # Invalid float to integer casts:
+    with np.errstate(over="ignore"):
+        for to_dt in np.typecodes["AllInteger"]:
+            for value in [np.inf, np.nan]:
+                for from_dt in np.typecodes["AllFloat"]:
+                    from_dt = np.dtype(from_dt)
+                    from_val = from_dt.type(value)
+
+                    yield param(from_val, to_dt, id=f"{from_val}-to-{to_dt}")
+
+
+def check_operations(dtype, value):
+    """
+    There are many dedicated paths in NumPy which cast and should check for
+    floating point errors which occurred during those casts.
+    """
+    if dtype.kind != 'i':
+        def assignment():
+            arr = np.empty(3, dtype=dtype)
+            arr[0] = value
+
+        yield assignment
+
+        def fill():
+            arr = np.empty(3, dtype=dtype)
+            arr.fill(value)
+
+        yield fill
+
+    def copyto_scalar():
+        arr = np.empty(3, dtype=dtype)
+        np.copyto(arr, value, casting="unsafe")
+
+    yield copyto_scalar
+
+    def copyto():
+        arr = np.empty(3, dtype=dtype)
+        np.copyto(arr, np.array([value, value, value]), casting="unsafe")
+
+    yield copyto
+
+    def copyto_scalar_masked():
+        arr = np.empty(3, dtype=dtype)
+        np.copyto(arr, value, casting="unsafe",
+                  where=[True, False, True])
+
+    yield copyto_scalar_masked
+
+    def copyto_masked():
+        arr = np.empty(3, dtype=dtype)
+        np.copyto(arr, np.array([value, value, value]), casting="unsafe",
+                  where=[True, False, True])
+
+    yield copyto_masked
+
+    def direct_cast():
+        np.array([value, value, value]).astype(dtype)
+
+    yield direct_cast
+
+    def direct_cast_nd_strided():
+        arr = np.full((5, 5, 5), fill_value=value)[:, ::2, :]
+        arr.astype(dtype)
+
+    yield direct_cast_nd_strided
+
+    def boolean_array_assignment():
+        arr = np.empty(3, dtype=dtype)
+        arr[[True, False, True]] = np.array([value, value])
+
+    yield boolean_array_assignment
+
+    def integer_array_assignment():
+        arr = np.empty(3, dtype=dtype)
+        values = np.array([value, value])
+
+        arr[[0, 1]] = values
+
+    #yield integer_array_assignment
+
+    def integer_array_assignment_with_subspace():
+        arr = np.empty((5, 3), dtype=dtype)
+        values = np.array([value, value, value])
+
+        arr[[0, 2]] = values
+
+    yield integer_array_assignment_with_subspace
+
+
+@pytest.mark.parametrize(["value", "dtype"], values_and_dtypes())
+@pytest.mark.filterwarnings("ignore::numpy.ComplexWarning")
+def test_floatingpoint_errors_casting(dtype, value):
+    dtype = np.dtype(dtype)
+    for operation in check_operations(dtype, value):
+        dtype = np.dtype(dtype)
+
+        match = "invalid" if dtype.kind in 'iu' else "overflow"
+        with pytest.warns(RuntimeWarning, match=match):
+            operation()
+
+        with np.errstate(all="raise"):
+            with pytest.raises(FloatingPointError, match=match):
+                operation()