MAINT: pow1pm1: adopt the convention pow1pm1(-1, 0) is 0.

WarrenWeckesser · Jun 18, 2024 · af85b85 · af85b85
1 parent e0812d3
commit af85b85
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Showing 4 changed files with 12 additions and 3 deletions.
diff --git a/pyproject.toml b/pyproject.toml
@@ -8,7 +8,7 @@ requires = [
 
 [project]
 name = 'ufunclab'
-version = '0.0.8.dev8'
+version = '0.0.8.dev9'
 description = 'NumPy ufuncs and utilities.'
 readme = 'README.md'
 requires-python = '>=3.9'

diff --git a/src/pow1pm1/define_cxxgen_extmods.py b/src/pow1pm1/define_cxxgen_extmods.py
@@ -12,6 +12,9 @@
 
 `nan` is returned when `x < -1`.
 
+The function follows the widely used convention that `pow(0, 0)`
+is 1, so `pow1pm1(-1, 0)` is 0.0.
+
 Parameters
 ----------
 x : array_like

diff --git a/src/pow1pm1/pow1pm1.h b/src/pow1pm1/pow1pm1.h
@@ -11,8 +11,9 @@
 template<typename T>
 T pow1pm1(T x, T y)
 {
-    // XXX Maybe handle (x, y) == (-1, 0) as a special case, and return 0
-    // instead of nan?
+    if (x == -1.0 && y == 0.0) {
+        return static_cast<T>(0.0);
+    }
     return std::expm1(y * std::log1p(x));
 }
 

diff --git a/ufunclab/tests/test_pow1pm1.py b/ufunclab/tests/test_pow1pm1.py
@@ -10,3 +10,8 @@
 def test_logexpint1(x, y, expected):
     z = pow1pm1(x, y)
     assert_allclose(z, expected, rtol=1e-15)
+
+
+def test_edge_case():
+    w = pow1pm1(-1.0, 0.0)
+    assert w == 0.0