Underflow and Denormal Numbers

• When de-normalized numbers emerge in a computation (i.e. numbers x<DBL_MIN) they are flushed to zero by default:

• will print zero. To force IEEE-754 gradual underflow it is necessary to manipulate status register on the R1x000 cpu.

• Calling no_flush at the beginning of the program will print

• 0.22250738585072014D-308

• Flush-to-zero property can lead to x-y=0, while x?y .

• Keeping de-normalized numbers in computations will avoid that condition, but will cause

• fp exception, that must be processed in software.

• It is a performance issue - not to manipulate the de-normalized numbers in calculations.

Program denorm

real*8 a,b

a = 2.2250738585072014D-308

b = a/10.0D0

write(6,10) b

end

#include <sys/fpu.h>

void no_flush_()

{

union fpc_csr f;

f.fc_word = get_fpc_csr();

f.fc_struct.flush = 0;

set_fpc_csr(f.fc_word);

}

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