commit 8f9f8d612a1ee264a465f493b1ce6215418128de
author Victor Stinner <victor.stinner@haypocalc.com> Mon May 09 12:45:41 2011 +0200
committer Victor Stinner <victor.stinner@haypocalc.com> Mon May 09 12:45:41 2011 +0200
tree 932bbe3ba95806fc499f853fe25c2ec3726c6afa
parent 936d518dc8fb8fb094de1391d5a0703287db694e

Issue #11888: Use system log2() when available

I expect the system libc to use more accurate functions than Python. The GNU
libc uses for example FYL2X and FYL2XP1 hardware instructions on Intel FPU.

Modules/mathmodule.c

diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 14d008a..cebb4ff 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -602,6 +602,9 @@
     }
 
     if (x > 0.0) {
+#ifdef HAVE_LOG2
+        return log2(x);
+#else
         double m;
         int e;
         m = frexp(x, &e);
@@ -617,6 +620,7 @@
         else {
             return log(m) / log(2.0) + e;
         }
+#endif
     }
     else if (x == 0.0) {
         errno = EDOM;