Re: [ANN] Lua 5.4.0 (work2) now available
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- Subject: Re: [ANN] Lua 5.4.0 (work2) now available
- From: Albert Chan <albertmcchan@...>
- Date: 2018年8月26日 18:58:48 -0400
> Going down all the way, the multiplication used in 5.3 to test
> the sign of the result may underflow:
>
> $ Lua 5.3.2 Copyright (C) 1994-2015 Lua.org, PUC-Rio
>> -2.1^-1000 % 2^-1000
> -5.928787750095e-323
>
> The result should be non negative, in the range [0,2^-1000).
>
> -- Roberto
Good catch !
FYI, even with underflow, the sign bit is still there.
double a = -6e-323, b = 0x1p-1000, c = a*b;
printf("c = %g, sign_bit = %#x\n", c, signbit(c));
c = 0, sign_bit = 0x200
However, signbit test is too good, fmod test like this:
if (signbit((m)*(b)) && (m) != 0) (m) += (b);