Issue #11888: Add log2 function to math module. Patch written by Mark
Dickinson.
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index 98c5b33..8254d3f 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -184,6 +184,13 @@
    result is calculated in a way which is accurate for *x* near zero.
 
 
+.. function:: log2(x)
+
+   Return the base-2 logarithm of *x*.
+
+   .. versionadded:: 3.3
+
+
 .. function:: log10(x)
 
    Return the base-10 logarithm of *x*.  This is usually more accurate