From 8e29a024c6f48d3a15c679ee8d1b9555dcea8b4f Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Sun, 3 Dec 2023 12:05:08 +0100
Subject: [PATCH] Return 1 if NaN, 0 otherwise

---
 Doc/c-api/hash.rst              | 8 ++++----
 Lib/test/test_capi/test_hash.py | 7 +++++--
 Python/pyhash.c                 | 8 ++++----
 3 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/Doc/c-api/hash.rst b/Doc/c-api/hash.rst
index 190a726958438d9..fd12d6204f0e057 100644
--- a/Doc/c-api/hash.rst
+++ b/Doc/c-api/hash.rst
@@ -52,16 +52,16 @@ Functions
 
    Hash a C double number.
 
-   * Set *\*result* to the hash and return ``1`` if *value* is finite or is
+   * Set *\*result* to the hash and return ``0`` if *value* is finite or is
      infinity.
    * Set *\*result* to :data:`sys.hash_info.nan <sys.hash_info>` (``0``) and
-     return ``0`` if *value* is not-a-number (NaN).
+     return ``1`` if *value* is not-a-number (NaN).
 
    *result* must not be ``NULL``.
 
    .. note::
-      Only rely on the function return value to distinguish the "not-a-number"
-      case. *\*result* can be ``0`` if *value* is finite. For example,
+      Only rely on the function return value to distinguish the not-a-number
+      (NaN) case. *\*result* can be ``0`` if *value* is finite. For example,
       ``Py_HashDouble(0.0, &result)`` sets *\*result* to 0.
 
    .. versionadded:: 3.13
diff --git a/Lib/test/test_capi/test_hash.py b/Lib/test/test_capi/test_hash.py
index 68bdcd8ccf0469e..7d2c6c437044312 100644
--- a/Lib/test/test_capi/test_hash.py
+++ b/Lib/test/test_capi/test_hash.py
@@ -35,10 +35,13 @@ def test_hash_getfuncdef(self):
 
     def test_hash_double(self):
         # Test Py_HashDouble()
+        #
+        # _Py_HashDouble() is tested indirectly by test_float in test_hash()
+        # and test_hash_nan().
         hash_double = _testcapi.hash_double
 
         def check_number(value, expected):
-            self.assertEqual(hash_double(value), (1, expected))
+            self.assertEqual(hash_double(value), (0, expected))
 
         # test some integers
         integers = [
@@ -74,4 +77,4 @@ def check_number(value, expected):
                 check_number(-x, hash(-x))
 
         # test not-a-number (NaN)
-        self.assertEqual(hash_double(float('nan')), (0, sys.hash_info.nan))
+        self.assertEqual(hash_double(float('nan')), (1, sys.hash_info.nan))
diff --git a/Python/pyhash.c b/Python/pyhash.c
index 6fa79d08c288213..d43bb39985985dd 100644
--- a/Python/pyhash.c
+++ b/Python/pyhash.c
@@ -95,12 +95,12 @@ Py_HashDouble(double v, Py_hash_t *result)
     if (!Py_IS_FINITE(v)) {
         if (Py_IS_INFINITY(v)) {
             *result = (v > 0 ? _PyHASH_INF : -_PyHASH_INF);
-            return 1;
+            return 0;
         }
         else {
             assert(Py_IS_NAN(v));
             *result = _PyHASH_NAN;
-            return 0;
+            return 1;
         }
     }
 
@@ -134,7 +134,7 @@ Py_HashDouble(double v, Py_hash_t *result)
     if (x == (Py_uhash_t)-1)
         x = (Py_uhash_t)-2;
     *result = (Py_hash_t)x;
-    return 1;
+    return 0;
 }
 
 Py_hash_t
@@ -143,7 +143,7 @@ _Py_HashDouble(PyObject *obj, double v)
     assert(obj != NULL);
 
     Py_hash_t hash;
-    if (Py_HashDouble(v, &hash) == 0) {
+    if (Py_HashDouble(v, &hash) == 1) {
         hash = _Py_HashPointer(obj);
     }
     return hash;