Ruby最大整数

Question

我需要能够确定Ruby中的系统最大整数.有人知道怎么样,或者有可能吗？

Answer 1

FIXNUM_MAX = (2**(0.size * 8 -2) -1)
FIXNUM_MIN = -(2**(0.size * 8 -2))

Answer 2

Ruby在溢出时自动将整数转换为大整数类,因此(实际上)它们的大小没有限制.

如果您正在寻找机器的大小,即64位或32位,我在ruby-forum.com上找到了这个技巧:

machine_bytes = ['foo'].pack('p').size
machine_bits = machine_bytes * 8
machine_max_signed = 2**(machine_bits-1) - 1
machine_max_unsigned = 2**machine_bits - 1

如果您正在寻找Fixnum对象的大小(小到足以存储在单个机器字中的整数),您可以调用0.size以获取字节数.我猜它应该是32位版本的4,但我现在无法测试.此外,最大的Fixnum显然是2**30 - 1(或2**62 - 1),因为一位用于将其标记为整数而不是对象引用.

Answer 3

阅读友好的手册？谁想要这样做？

start = Time.now
largest_known_fixnum = 1
smallest_known_bignum = nil

until smallest_known_bignum == largest_known_fixnum + 1
  if smallest_known_bignum.nil?
    next_number_to_try = largest_known_fixnum * 1000
  else
    next_number_to_try = (smallest_known_bignum + largest_known_fixnum) / 2 # Geometric mean would be more efficient, but more risky
  end

  if next_number_to_try <= largest_known_fixnum ||
       smallest_known_bignum && next_number_to_try >= smallest_known_bignum
    raise "Can't happen case" 
  end

  case next_number_to_try
    when Bignum then smallest_known_bignum = next_number_to_try
    when Fixnum then largest_known_fixnum = next_number_to_try
    else raise "Can't happen case"
  end
end

finish = Time.now
puts "The largest fixnum is #{largest_known_fixnum}"
puts "The smallest bignum is #{smallest_known_bignum}"
puts "Calculation took #{finish - start} seconds"

Answer 4

在ruby Fixnums中自动转换为Bignums.

要找到最高可能的Fixnum,您可以执行以下操作:

class Fixnum
 N_BYTES = [42].pack('i').size
 N_BITS = N_BYTES * 8
 MAX = 2 ** (N_BITS - 2) - 1
 MIN = -MAX - 1
end
p(Fixnum::MAX)

从一个红宝石谈话讨论中无耻地撕掉了.看那里了解更多细节.