Add shader test for nan/inf detection (#473)

Author: almarklein

tests/test_not_finite.py

@@ -0,0 +1,249 @@
+"""
+A collection of tests related to non-finite values in shaders, like nan and inf.
+
+See:
+* https://en.wikipedia.org/wiki/NaN
+* https://github.com/gpuweb/gpuweb/pull/2311#issuecomment-1973533433
+
+"""
+
+import ctypes
+
+import numpy as np
+
+from wgpu.utils.compute import compute_with_buffers
+from pytest import skip
+from testutils import can_use_wgpu_lib
+
+
+if not can_use_wgpu_lib:
+    skip("Skipping tests that need the wgpu lib", allow_module_level=True)
+
+
+def test_finite_using_nequal():
+    # Just to demonstrate that this does not work.
+    # The compiler filters optimizes away the check.
+
+    shader = """
+        @group(0)
+        @binding(0)
+        var<storage,read> values: array<f32>;
+
+        fn is_nan(v:f32) -> bool {
+            return v != v;
+        }
+
+        fn is_inf(v:f32) -> bool {
+            return v != 0.0 && v * 2.0 == v;
+        }
+
+        fn is_finite(v:f32) -> bool {
+            return v == v && v * 2.0 != v;
+        }
+
+        fn to_real(v:f32) -> f32 {
+            return select(0.0, v, is_finite(v));
+        }
+
+    """
+
+    detect_finites("nequal", shader, False, False)
+
+
+def test_finite_using_min_max():
+    # This obfuscates the check for equality enough for the compiler
+    # not to optimize it away.
+    #
+    # However, if fastmath is enabled, depending on the hardare/compiler,
+    # the loaded value may not actually be a nan/inf anymore.
+
+    shader = """
+        @group(0)
+        @binding(0)
+        var<storage,read> values: array<f32>;
+
+        fn is_nan(v:f32) -> bool {
+            return min(v, 1.0) == 1.0 && max(v, -1.0) == -1.0;
+        }
+
+        fn is_inf(v:f32) -> bool {
+            return v != 0.0 && v * 2.0 == v;
+        }
+
+        fn is_finite(v:f32) -> bool {
+            return !is_nan(v) && !is_inf(v);
+        }
+
+        fn to_real(v:f32) -> f32  {
+            return select(0.0, v, is_finite(v));
+        }
+
+    """
+
+    detect_finites("min-max", shader, True, True)
+
+
+def test_finite_using_uint():
+    # This is the most reliable approach.
+
+    shader = """
+        @group(0)
+        @binding(0)
+        var<storage,read> values: array<u32>;
+
+        fn is_nan(v:u32) -> bool {
+            let mask = 0x7F800000u;
+            let v_is_pos_inf = v == 0x7F800000u;
+            let v_is_neg_inf = v == 0xFF800000u;
+            let v_is_finite = (v & mask) != mask;
+            return !v_is_finite & !(v_is_pos_inf | v_is_neg_inf);
+        }
+
+        fn is_inf(v:u32) -> bool {
+            let v_is_pos_inf = v == 0x7F800000u;
+            let v_is_neg_inf = v == 0xFF800000u;
+            return v_is_pos_inf | v_is_neg_inf;
+        }
+
+        fn is_finite(v:u32) -> bool {
+            return (v & 0x7F800000u) != 0x7F800000u;
+        }
+
+        fn to_real(v:u32) -> f32 {
+            return select(0.0, bitcast<f32>(v), is_finite(v));
+        }
+    """
+
+    detect_finites("uint", shader, True, True)
+
+
+def detect_finites(title, shader, expect_detection_nan, expect_detection_inf):
+
+    base_shader = """
+
+        @group(0)
+        @binding(1)
+        var<storage,read_write> result_nan: array<i32>;
+
+        @group(0)
+        @binding(2)
+        var<storage,read_write> result_inf: array<i32>;
+
+        @group(0)
+        @binding(3)
+        var<storage,read_write> result_finite: array<i32>;
+
+        @group(0)
+        @binding(4)
+        var<storage,read_write> result_real: array<f32>;
+
+        @compute
+        @workgroup_size(1)
+        fn main(@builtin(global_invocation_id) index: vec3<u32>) {
+            let i = i32(index.x);
+            let value = values[i];
+
+            result_nan[i] = i32(is_nan(value));
+            result_inf[i] = i32(is_inf(value));
+            result_finite[i] = i32(is_finite(value));
+            result_real[i] = to_real(value);
+
+        }
+
+    """
+
+    # Create data in blocks of 10: zeros, nans, infs, random reals
+    parts = [
+        [0.0] * 10,
+        [
+            float("nan"),
+            np.nan,
+            np.nan,
+            np.nan,
+            np.nan,
+            np.nan,
+            np.nan,
+            np.nan,
+            np.nan,
+            np.nan,
+        ],
+        [
+            float("-inf"),
+            float("inf"),
+            -np.inf,
+            np.inf,
+            np.inf,
+            np.inf,
+            np.inf,
+            np.inf,
+            np.inf,
+            np.inf,
+        ],
+        np.random.uniform(-1e9, 1e9, 10),
+    ]
+    values = np.concatenate(parts, dtype=np.float32)
+
+    # Check length
+    assert values.shape == (40,)
+    n = len(values)
+
+    # Create reference bool arrays
+    is_nan_ref = np.zeros((n,), bool)
+    is_nan_ref[10:20] = True
+    is_inf_ref = np.zeros((n,), bool)
+    is_inf_ref[20:30] = True
+    is_finite_ref = np.ones((n,), bool)
+    is_finite_ref[10:30] = False
+
+    # Get reference real array
+    real_ref = values.copy()
+    real_ref[~is_finite_ref] = 0
+
+    # Compute!
+    out = compute_with_buffers(
+        {0: (ctypes.c_float * n)(*values)},
+        {
+            1: n * ctypes.c_int32,
+            2: n * ctypes.c_int32,
+            3: n * ctypes.c_int32,
+            4: n * ctypes.c_float,
+        },
+        shader + base_shader,
+    )
+    is_nan = out[1]
+    is_inf = out[2]
+    is_finite = out[3]
+    real = out[4]
+
+    # Check that numpy detects ok
+    assert np.all(np.isnan(values) == is_nan_ref)
+    assert np.all(np.isinf(values) == is_inf_ref)
+    assert np.all(np.isfinite(values) == is_finite_ref)
+
+    # Check that our shader does too
+    detected_nan = bool(np.all(is_nan == is_nan_ref))
+    detected_inf = bool(np.all(is_inf == is_inf_ref))
+    detected_finite = bool(np.all(is_finite == is_finite_ref))
+    good_reals = bool(np.all(real == real_ref))
+
+    # Print, for when run as a script
+    checkmark = lambda x: "x✓"[x]  # noqa
+    print(
+        f"{title:>10}:   {checkmark(detected_nan)} is_nan   {checkmark(detected_inf)} is_inf   {checkmark(detected_finite)} is_finite   {checkmark(good_reals)} good_reals"
+    )
+
+    # Test
+    if expect_detection_nan:
+        assert detected_nan
+    if expect_detection_inf:
+        assert detected_inf
+    if expect_detection_nan and expect_detection_inf:
+        assert detected_finite
+        assert good_reals
+
+
+if __name__ == "__main__":
+
+    test_finite_using_nequal()
+    test_finite_using_min_max()
+    test_finite_using_uint()