Newbie questions
Raimo Niskanen
raimo@REDACTED
Fri Mar 31 13:23:55 CEST 2006
svenolof@REDACTED (Sven-Olof Nystr|m) writes:
> Richard A. O'Keefe writes:
> > Nick Linker <xlcr@REDACTED> wrote:
> > I'm sorry, but I meant quite different question: given a big
> > number N, how to compute the number of digits?
> >
> > There is obvious solution: length(integer_to_list(N)), but it
> > is not very efficient. I wanted to have a bit faster
> > solution... Ok, nevermind.
> >
> > I'm aware of (and have used) several programming languages providing
> > as-long-as-necessary integer arithmetic. Without consulting manuals
> > (everything is being moved out of my office so that new carpet can
> > be laid) it's hard to be sure, but from memory, NONE of them provides
> > an operation "how many decimal digits in this bignum". Common Lisp
> > has HAULONG, which tells you about how many BITS, and Java's
> > BigInteger class offers bitLength(), which again tells you how many
> > BITS. In Smalltalk, the obvious thing to do would be n printString size,
> > and in Scheme it would be (string-length (number->string n)).
>
>
> You seem to have your Lisps confused :-). Haulong is a function in
> MacLisp; the corresponding operation in Common Lisp is
> integer-length. Both functions give the length of the integer in bits.
>
> > It's not completely clear what you want. Is the "number of digits"
> > in -123456890123456890 twenty (literally the number of digits) or
> > twenty-one (the number of characters in the minimal decimal representation)?
>
> Curiously, both CL's integer-length and Java's bitLength() define the
> length of negative numbers so that -1 has length 0 (same as the length
> of 0, of course).
>
That seems to be some kind of 2-complement notion of bit length.
If you define the bit length of negative numbers to be the number
of bits from the right to the last non-1 as opposed to for
positive numbers to the last non-0, you would get this.
>
> Sven-Olof
>
--
/ Raimo Niskanen, Erlang/OTP, Ericsson AB
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