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.
diff --git a/configure.in b/configure.in
index 49864f4..c6a9437 100644
--- a/configure.in
+++ b/configure.in
@@ -2512,7 +2512,7 @@
futimens futimes \
gai_strerror getgroups getlogin getloadavg getpeername getpgid getpid \
getpriority getresuid getresgid getpwent getspnam getspent getsid getwd \
- initgroups kill killpg lchmod lchown lockf linkat lstat lutimes mbrtowc mkdirat mkfifo \
+ initgroups kill killpg lchmod lchown lockf log2 linkat lstat lutimes mbrtowc mkdirat mkfifo \
mkfifoat mknod mknodat mktime mremap nice openat pathconf pause plock poll \
posix_fallocate posix_fadvise pread \
pthread_init pthread_kill putenv pwrite readlink readlinkat readv realpath renameat \
@@ -3368,7 +3368,7 @@
LIBS="$LIBS $LIBM"
AC_CHECK_FUNCS([acosh asinh atanh copysign erf erfc expm1 finite gamma])
-AC_CHECK_FUNCS([hypot lgamma log1p round tgamma])
+AC_CHECK_FUNCS([hypot lgamma log1p log2 round tgamma])
AC_CHECK_DECLS([isinf, isnan, isfinite], [], [], [[#include <math.h>]])
# On FreeBSD 6.2, it appears that tanh(-0.) returns 0. instead of