It seems that 80-bit pseudo-denormals (that is, 80-bit extended floats with exponent of zero and significand greater than 0x8000000000000000) are not handled properly. For example, there is an unhandled overflow here:
(i.e. if you add the smallest denormal w/ significand 0x0000000000000001 to the largest pseudo-denormal w/ significand 0xffffffffffffffff, SoftFloat gives zero as the answer.)
I don't know if handling pseudo-denormals is within the scope of Berkeley Softfloat. But since the 80-bit extended format is fairly specific to Intel x87 FPUs, it seems like pseudo-denormals should be handled just as x87 handles them.
It seems that 80-bit pseudo-denormals (that is, 80-bit extended floats with exponent of zero and significand greater than 0x8000000000000000) are not handled properly. For example, there is an unhandled overflow here:
berkeley-softfloat-3/source/s_addMagsExtF80.c
Line 84 in a0c6494
(i.e. if you add the smallest denormal w/ significand 0x0000000000000001 to the largest pseudo-denormal w/ significand 0xffffffffffffffff, SoftFloat gives zero as the answer.)
I don't know if handling pseudo-denormals is within the scope of Berkeley Softfloat. But since the 80-bit extended format is fairly specific to Intel x87 FPUs, it seems like pseudo-denormals should be handled just as x87 handles them.