1 files changed, 75 insertions, 0 deletions
diff --git a/missing/nextafter.c b/missing/nextafter.c
new file mode 100644
index 0000000000..116a0d376b
--- /dev/null
+++ b/missing/nextafter.c
@@ -0,0 +1,75 @@
+#include <math.h>
+#include <float.h>
+
+/* This function doesn't set errno.  It should on POSIX, though. */
+
+double
+nextafter(double x, double y)
+{
+    double x1, x2, d;
+    int e;
+
+    if (isnan(x))
+        return x;
+    if (isnan(y))
+        return y;
+
+    if (x == y)
+        return y;
+
+    if (x == 0) {
+        /* the minimum "subnormal" float */
+        x1 = ldexp(0.5, DBL_MIN_EXP - DBL_MANT_DIG + 1);
+        if (x1 == 0)
+            x1 = DBL_MIN; /* the minimum "normal" float */
+        if (0 < y)
+            return x1;
+        else
+            return -x1;
+    }
+
+    if (x < 0) {
+        if (isinf(x))
+            return -DBL_MAX;
+        if (x == -DBL_MAX && y < 0 && isinf(y))
+            return y;
+    }
+    else {
+        if (isinf(x))
+            return DBL_MAX;
+        if (x == DBL_MAX && 0 < y && isinf(y))
+            return y;
+    }
+
+    x1 = frexp(x, &e);
+
+    if (x < y) {
+        d = DBL_EPSILON/2;
+        if (x1 == -0.5) {
+            x1 *= 2;
+            e--;
+        }
+    }
+    else {
+        d = -DBL_EPSILON/2;
+        if (x1 == 0.5) {
+            x1 *= 2;
+            e--;
+        }
+    }
+
+    if (e < DBL_MIN_EXP) {
+        d = ldexp(d, DBL_MIN_EXP-e);
+    }
+
+    x2 = x1 + d;
+
+    if (x2 == 0.0) {
+        if (x1 < 0)
+            return -0.0;
+        else
+            return +0.0;
+    }
+
+    return ldexp(x2, e);
+}