fix: 🐛 do not generate inf values if elements has infinity disabled f…

…or bfloat16 tensors.

Before, if a float strategy that prevented infinities was provided to as `elements` to `tensor_strategy`, the resultant tensor could still occasionally have infinities because the strategy would generate float32 values that exceeded the maximium/minimum values for bfloat16.

hypothesis_torch/dtype.py

@@ -50,7 +50,7 @@
     torch.float16: np.float16,
     torch.float32: np.float32,
     torch.float64: np.float64,
-    torch.bfloat16: np.float32,  # Numpy does not have a bf16, but it has the same dynamic range as f32
+    torch.bfloat16: np.float32,  # Numpy does not have a bf16, but it is a strict subset of fp32
     torch.complex64: complex,
     torch.complex128: complex,
     torch.bool: np.bool_,
@@ -60,7 +60,7 @@
 
 float_width_map: Final[Mapping[torch.dtype, Literal[16, 32, 64]]] = {
     torch.float16: 16,
-    torch.bfloat16: 32,  # Numpy does not have a bf16, but it has the same dynamic range as f32
+    torch.bfloat16: 32,  # Numpy does not have a bf16, but it is a strict subset of f32
     torch.float32: 32,
     torch.float64: 64,
 }

hypothesis_torch/tensor.py

@@ -95,14 +95,14 @@ def tensor_strategy(
     if isinstance(device, st.SearchStrategy):
         device = draw(device)
     # MPS devices do not support tensors with dtype torch.float64 and bfloat16
-    hypothesis.assume(not (device is not None and device.type == "mps" and dtype in (torch.float64, torch.bfloat16)))
+    hypothesis.assume(device is None or device.type != "mps" or dtype not in (torch.float64, torch.bfloat16))
 
     if layout is None:
         layout = st.from_type(torch.layout)
     if isinstance(layout, st.SearchStrategy):
         layout = draw(layout)
     # MPS devices do not support sparse tensors
-    hypothesis.assume(not (device is not None and device.type == "mps" and layout == torch.sparse_coo))
+    hypothesis.assume(device is None or device.type != "mps" or layout != torch.sparse_coo)
 
     # If the dtype is an integer, we need to make sure that the elements are integers within the dtype's range
     if dtype in dtype_module.INT_DTYPES and isinstance(elements, st.SearchStrategy):
@@ -112,6 +112,14 @@ def tensor_strategy(
     # If the dtype is a float, then we need to make sure that only elements that can be represented exactly are
     # generated
     if dtype in dtype_module.FLOAT_DTYPES and elements is not None:
+        if dtype == torch.bfloat16:
+            # Since we do not directly support bfloat16 in numpy, we will generate float32.
+            # This still means that we will occasionally generate values that exceed the max/min of bfloat16.
+            # All other values (within the range) will be simply truncated below when casting the numpy array to
+            # a bfloat16 tensor.
+            bfloat16_info = torch.finfo(torch.bfloat16)
+            elements = elements.filter(lambda x: bfloat16_info.min <= x <= bfloat16_info.max)
+
         width = dtype_module.float_width_map[dtype]
         if width < 64:
 
@@ -129,9 +137,9 @@ def downcast(x: float) -> float:
                     The downcasted float.
                 """
                 try:
-                    return float_of(x, width)
+                    return hypothesis.internal.floats.float_of(x, width)
                 except OverflowError:  # pragma: no cover
-                    reject()
+                    hypothesis.reject()
 
             elements = elements.map(downcast)