+int l[N];

+float l_2[N];

+void init(int* x, int n)

+		l_2[i] = (ii==0) ? 0.0f : 1.0f/ii;            // avoid division by 0 !

+	for (int i=0; i<n; i++)  x[i] = i*(i+1);

+	x[100] = 0;	// add some zeros at random places

+	x[30] = 0;

+* 1) By default the compiler assumes exceptions can occur. Compile with:

+* 	gcc -O3 -lm test_fpexcept.c

+* run ./a.out prints "0 0"

+* 

+* 2) Now tell the compiler no exceptions will occur, to enable further optimizations. Compile with:

+*     gcc -O3 -fno-trapping-math -lm test_fpexcept.c

+* run ./a.out generates a spurious exception.

+*/

+

+

+#define _GNU_SOURCE

+#include <stdio.h>

+#include <fenv.h>

+

+

+#define N 1000

+double l[N];

+double l_2[N];

+

+void init(double* x, int n)

+{

+	for (int i=0; i<n; i++)  l[i] = i*(i+1);

+	l[100] = 0;	// add some zeros at random places

+	l[30] = 0;

+}

+

+

+int main()

+{

+	init(l,N);

+

+	// -fno-trapping-math basically tells the compiler (among other things) we will NOT call the following line:

+	feenableexcept(FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW);                // turn this on to track NaNs or other floating-point exceptions (requires gcc, #define _GNU_SOURCE and #include <fenv.h>)

+

+	// This loop can be vectorized when compiled with -fno-trapping-math

+	for (int i=0; i<N; i++) {

+		int ii = l[i];

+		l_2[i] = (ii==0) ? 0.0 : 1.0/ii;            // avoid division by 0 !

+	}

+

+	printf("%g %g\n", l_2[30], l_2[100]);		// do something with data to avoid eliminating all code.