Get exponent from a scientific notation

Question

How do we extract the exponent and sign from a "scientific" notation?

If we print a double value with printf("%lf %e") it shows par ex.:

   normal   scientific
   ------   ----------
   -888.3   -8.88e2    
    1.23     1.23e0    
    3.001    3.1e-1

x = floor(log10(N))

works only for positive values N. With -N it shows -nan(ind). Obviously Log10() with negatie value is not allowed.

Is [this](http://stackoverflow.com/questions/15685181/how-to-get-the-sign-mantissa-and-exponent-of-a-floating-point-number) what you are looking for? — SamVanDonut, Jan 13 '17 at 18:27
Why not just keep track of the sign with `bool neg = signbit(N);`, then reapply signed-ness after calculating `floor(log10(abs(N)))`? — Justin Time - Reinstate Monica, Jan 13 '17 at 19:58

score 2 · Answer 1 · answered Jan 13 '17 at 16:21

2

You don't care about the sign of the number, you need the exponent only, so you can get rid of the sign safely:

log10(abs(N))

Where abs returns the absolute value of N, which is always non-negative and thus can be used as an argument to log10.

answered Jan 13 '17 at 16:21

ForceBru

I need the sign too. Ex -3 or 3 is a big difference – Tom Tom Jan 13 '17 at 16:35
@TomTom, my answer is about removing the sign of _the number_, not the exponent. – ForceBru Jan 13 '17 at 16:36

1 Answers1