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usr/lib/libcervus/math/isnan.c

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+#include <math.h>
+#include <stdint.h>
+
+int isnan(double x) {
+    union {
+        double f;
+        uint64_t i;
+    } u = { .f = x };
+
+    uint64_t exp = (u.i >> 52) & 0x7FF;
+    uint64_t mantissa = u.i & 0xFFFFFFFFFFFFFULL;
+
+    return (exp == 0x7FF) && (mantissa != 0);
+}