Biggest number

ruby-talk
1

I'm learning ruby, and I want to know if it is any way to know the
biggest number to be represented with a specific type of number (Fixnum,
Bignum, Float).

Thank you.

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Posted via http://www.ruby-forum.com/.

2

Javier Esteve wrote:

I'm learning ruby, and I want to know if it is any way to know the
biggest number to be represented with a specific type of number (Fixnum,
Bignum, Float).

Float is a standard 64-bit IEEE floating point value. There are several constants on the Float class that can tell you whatever you need:

➔ jruby -e "p Float::constants"
["MAX", "MAX_10_EXP", "MANT_DIG", "RADIX", "DIG", "MIN", "ROUNDS", "MIN_EXP", "EPSILON", "MIN_10_EXP", "MAX_EXP"]

Fixnum has no such constants, but on most implementations (CRuby, JRuby, Rubinius at least) its max size is dependent on how large its basis representation is. I believe it can be either "32" or "64" bits on CRuby, where on JRuby it is always "64" bits:

➔ ruby -e "p (1 << (1.size * 8 - 1)) - 1"
2147483647

➔ ruby -e "p -(1 << (1.size * 8 - 1))"
-2147483648

➔ jruby -e "p (1 << (1.size * 8 - 1)) - 1"
9223372036854775807

➔ jruby -e "p -(1 << (1.size * 8 - 1))"
-9223372036854775808

The loss of one bit of precision on most impls is to emulate CRuby's implementation of Fixnum as a tagged pointer, where the top bit indicates whether an object pointer is a real pointer or a Fixnum value).

And Bignum has no min or max size, other than the maximum size of a byte on your system.

- Charlie

3

Javier Esteve wrote:

I'm learning ruby, and I want to know if it is any way to know the
biggest number to be represented with a specific type of number (Fixnum,
Bignum, Float).

Thank you.

irb(main):005:0> (2**30).class
=> Bignum
irb(main):006:0> (2**30-1).class
=> Fixnum

irb(main):009:0> RUBY_VERSION
=> "1.8.6"

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       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407