# Class: Integer

Inherits:
Object
show all
Defined in:
lib/epitools/core_ext/numbers.rb,
lib/epitools/core_ext/truthiness.rb

## Constant Summary collapse

BASE_DIGITS =

Cached constants for encoding numbers into bases up to 64

[*'0'..'9', *'A'..'Z', *'a'..'z', '_', '-']
SMALL_POWERS_OF_2 =
{2=>1, 4=>2, 8=>3, 16=>4, 32=>5, 64=>6}

## Instance Method Summary collapse

• 'true' if the integer is 0.

• #fact ⇒ Object (also: #factorial)

Factorial.

• Returns the all the prime factors of a number.

• #fib ⇒ Object (also: #fibonacci)

Fibonacci (recursive style).

• Flip all bits except the sign bit.

• Am I a prime number?.

• Return a specified number of primes (optionally starting at the argument).

• Convert a number into a string representation (encoded in a base <= 64).

• #to_bits ⇒ Object (also: #bits)

Convert the number to an array of bits (least significant digit first, or little-endian).

• Convert the number into a hexadecimal string representation.

## Instance Method Details

### #blank? ⇒ Boolean

'true' if the integer is 0

Returns:

• (Boolean)
 61 # File 'lib/epitools/core_ext/truthiness.rb', line 61 def blank?; self == 0; end

### #fact ⇒ ObjectAlso known as: factorial

Factorial

 368 369 370 371 372 373 374 375 376 # File 'lib/epitools/core_ext/numbers.rb', line 368 def fact if self < 0 -(1..-self).reduce(:*) elsif self == 0 1 else (1..self).reduce(:*) end end

### #factors ⇒ Object

Returns the all the prime factors of a number.

 360 361 362 363 # File 'lib/epitools/core_ext/numbers.rb', line 360 def factors Prime # autoload the prime module prime_division.map { |n,count| [n]*count }.flatten end

### #fib ⇒ ObjectAlso known as: fibonacci

Fibonacci (recursive style)

 382 383 384 # File 'lib/epitools/core_ext/numbers.rb', line 382 def fib self < 2 ? self : (self-1).fib + (self-2).fib end

### #integer? ⇒ Boolean

Returns:

• (Boolean)
 63 # File 'lib/epitools/core_ext/truthiness.rb', line 63 def integer?; true; end

### #invert ⇒ Object

Flip all bits except the sign bit.

NOTE: This method should only be used with unsigned integers; if you use it with a signed integer, it will only flip the non-sign bits (I dunno if that's useful for anything; nothing comes to mind.)

 394 395 396 # File 'lib/epitools/core_ext/numbers.rb', line 394 def invert to_s(2).tr("01","10").to_i(2) end

### #prime? ⇒ Boolean

Am I a prime number?

Returns:

• (Boolean)
 337 338 339 # File 'lib/epitools/core_ext/numbers.rb', line 337 def prime? Prime.prime? self end

### #primes(starting_at = 2) ⇒ Object

Return a specified number of primes (optionally starting at the argument)

 344 345 346 347 348 349 350 351 352 353 354 355 # File 'lib/epitools/core_ext/numbers.rb', line 344 def primes(starting_at=2) result = [] current = starting_at loop do if current.prime? result << current return result if result.size >= self end current += 1 end end

### #to_base(base = 10) ⇒ Object

Convert a number into a string representation (encoded in a base <= 64).

The number is represented usiing the characters: 0..9, A..Z, a..z, _, -

(Setting base to 64 results in the encoding scheme that YouTube and url shorteners use for their ID strings, eg: www.youtube.com/watch?v=dQw4w9WgXcQ)

 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 # File 'lib/epitools/core_ext/numbers.rb', line 300 def to_base(base=10) raise "Error: Can't handle bases greater than 64" if base > 64 n = self digits = [] alphabet = BASE_DIGITS[0...base] if bits = SMALL_POWERS_OF_2[base] # a slightly accelerated version for powers of 2 mask = (2**bits)-1 loop do digits << (n & mask) n = n >> bits break if n == 0 end else # generic base conversion loop do n, digit = n.divmod(base) digits << digit break if n == 0 end end digits.reverse.map { |d| alphabet[d] }.join end

### #to_base62 ⇒ Object

 330 331 332 # File 'lib/epitools/core_ext/numbers.rb', line 330 def to_base62 to_base(62) end

### #to_bits ⇒ ObjectAlso known as: bits

Convert the number to an array of bits (least significant digit first, or little-endian).

 280 281 282 283 # File 'lib/epitools/core_ext/numbers.rb', line 280 def to_bits # TODO: Why does this go into an infinite loop in 1.8.7? ("%b" % self).chars.to_a.reverse.map(&:to_i) end

### #to_hex ⇒ Object

Convert the number into a hexadecimal string representation. (Identical to to_s(16), except that numbers < 16 will have a 0 in front of them.)

 273 274 275 # File 'lib/epitools/core_ext/numbers.rb', line 273 def to_hex "%0.2x" % self end