Hello, > I am working on a Z80 project and I needed 72 bits of precision for 64 > elements of the form log2(1+2^-i) (so log2(3/2), log2(5/4),...). I > needed to convert these to hexadecimal, and it worked until I tried > the following for i=56: > int(256*log(1+2^-56,2)) > > This returns 1, when in fact it should be 0. Actually, instead of > multiplying by 256, multiplying by 65536, or 600, or many other > numbers would also return the integer part as 1. > > As a note, I used RealField(80) as my precision.
Typing log(1 + 2^-56, 2) gives the result as a symbolic expression, not as an element of a real field. Applying int() to this internally uses a RealIntervalField with 53 bits of precision, which is not enough in this case. Here is a way to get the desired precision: sage: x = RealField(80)(256*log(1+2^-56,2)) sage: x 5.1254824061038682620123e-15 sage: int(x) 0 Peter -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.
