s2d vs MSVC/Clang

[ejb77]

i noticed that s2d disagrees with MSVC & CLang. Is this expected?

int main()
{
double d;
double e = 1.2999999999999999E+154;
s2d("1.2999999999999999E+154", &d);
assert(d==e); // assert occurs.
}

E

[ejb77]

d2s returns a number that is slightly different to what MSVC and CLang think they should be. d2s returns 1.2999999999999998e+154, the most insignificant bit is different.

(unsigned long long)&d,x 0x5fef06d5a4bf631e vs
(unsigned long long)&e,x 0x5fef06d5a4bf631f

[abolz]

This is due to an invalid shift value in multipleOfPowerOf2. I think a fix would be to change

ryu/ryu/s2d.c

Line 187 in 4cd47db

trailingZeros = e2 < e10 || multipleOfPowerOf2(m10, e2 - e10);

to

trailingZeros = e2 < e10 || (e2 - e10 < 64 && multipleOfPowerOf2(m10, e2 - e10));

and possibly adding an assert to multipleOfPowerOf2 to check the preconditions.

[ejb77]

thanks. this works great