Add nextup and nextdown math functions

TS 18661 adds nextup and nextdown functions alongside nextafter to provide
support for float128 equivalent to it.  This patch adds nextupl, nextup,
nextupf, nextdownl, nextdown and nextdownf to libm before float128 support.

The nextup functions return the next representable value in the direction of
positive infinity and the nextdown functions return the next representable
value in the direction of negative infinity.  These are currently enabled
as GNU extensions.

1 files changed, 4 insertions, 0 deletions

diff --git a/math/Versions b/math/Versions
index e6a597c..467d7ed 100644
--- a/math/Versions
+++ b/math/Versions
@@ -210,4 +210,8 @@ libm {
     # dynamic symbol for signgam but not __signgam.
     lgamma; lgammaf; lgammal; __signgam;
   }
+  GLIBC_2.24 {
+    nextup; nextupf; nextupl;
+    nextdown; nextdownf; nextdownl;
+  }
 }