1 files changed, 15 insertions, 0 deletions
diff --git a/Python/pymath.c b/Python/pymath.c
index 24b804223e..a08a0e7961 100644
--- a/Python/pymath.c
+++ b/Python/pymath.c
@@ -79,3 +79,18 @@ round(double x)
     return copysign(y, x);
 }
 #endif /* HAVE_ROUND */
+
+static const unsigned int BitLengthTable[32] = {
+    0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
+    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5
+};
+
+unsigned int _Py_bit_length(unsigned long d) {
+   unsigned int d_bits = 0;
+   while (d >= 32) {
+       d_bits += 6;
+       d >>= 6;
+   }
+   d_bits += BitLengthTable[d];
+   return d_bits;
+}