configure: Check for the math function rint

Add a fallback implementation if it doesn't exist.
Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -1124,6 +1124,7 @@ HAVE_LIST="
     poll_h
     posix_memalign
     rdtsc
+    rint
     round
     roundf
     rweflags
@@ -2954,6 +2955,7 @@ check_mathfunc log2
 check_mathfunc log2f
 check_mathfunc lrint
 check_mathfunc lrintf
+check_mathfunc rint
 check_mathfunc round
 check_mathfunc roundf
 check_mathfunc trunc

libavutil/libm.h

@@ -86,6 +86,13 @@ static av_always_inline av_const int isnan(float x)
 #define log2f(x) ((float)log2(x))
 #endif /* HAVE_LOG2F */
 
+#if !HAVE_RINT
+static inline double rint(double x)
+{
+    return x >= 0 ? floor(x + 0.5) : ceil(x - 0.5);
+}
+#endif /* HAVE_RINT */
+
 #if !HAVE_LRINT
 static av_always_inline av_const long int lrint(double x)
 {