third_party/pffft/patches/04-add_m_ln2.diff

diff --git a/third_party/pffft/src/test_pffft.c b/third_party/pffft/src/test_pffft.c
index ab78b4dcc0d5..deaf98ed9f09 100644
--- a/third_party/pffft/src/test_pffft.c
+++ b/third_party/pffft/src/test_pffft.c
@@ -45,6 +45,10 @@
 #  include <fftw3.h>
 #endif
 
+#ifndef M_LN2
+#define M_LN2 0.693147180559945309417
+#endif
+
 #define MAX(x,y) ((x)>(y)?(x):(y))
 
 double frand() {