From: Marc-Andre Lafortune <ruby-core@...>
Date: 2011-12-10T03:44:45+09:00
Subject: [ruby-core:41574] [ruby-trunk - Bug #5715] +/-1 ** Bignum returns different results than +/-1 ** Fixnum
Issue #5715 has been updated by Marc-Andre Lafortune.
Category set to core
Assignee set to Marc-Andre Lafortune
Just saw this update. Yes, as I stated, same issue as 5713. Yes the case for (-1) and bignum exponents can be fixed too. The case for 1 and 0 must be addressed for rational and float exponents too (but -1 will go to float for those)
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Bug #5715: +/-1 ** Bignum returns different results than +/-1 ** Fixnum
http://redmine.ruby-lang.org/issues/5715
Author: John Firebaugh
Status: Open
Priority: Normal
Assignee: Marc-Andre Lafortune
Category: core
Target version:
ruby -v: ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-darwin10.8.0]
=begin
Consider (({1 ** expt})) and (({(-1) ** expt})).
When ((|expt|)) is a Fixnum, the result is always 1, -1, Rational(1/1), or Rational(-1,1) depending on the signs of the operands and parity of the exponent.
When ((|expt|)) is a Bignum, Float 1.0 is always returned. Either the behavior for Fixnum exponents should be followed exactly (preferred), or at the very least -1.0 should be returned when the base is -1 and the exponent is odd.
$VERBOSE = nil
wordsize = 8 * 1.size
fixnum_max = 2 ** (wordsize - 2) - 1
fixnum_min = -2 ** (wordsize - 2)
[1, -1].each do |a|
[ 1, 2, fixnum_max, fixnum_max + 1, fixnum_max + 2,
-1, -2, fixnum_min, fixnum_min - 1, fixnum_min - 2].each do |b|
puts "%5s ** %20s (%s) == %5s" % [a, b, b.class, a ** b]
end
end
Output:
1 ** 1 (Fixnum) == 1
1 ** 2 (Fixnum) == 1
1 ** 4611686018427387903 (Fixnum) == 1
1 ** 4611686018427387904 (Bignum) == 1
1 ** 4611686018427387905 (Bignum) == 1
1 ** -1 (Fixnum) == 1/1
1 ** -2 (Fixnum) == 1/1
1 ** -4611686018427387904 (Fixnum) == 1/1
1 ** -4611686018427387905 (Bignum) == 1.0 # Bug
1 ** -4611686018427387906 (Bignum) == 1.0 # Bug
-1 ** 1 (Fixnum) == -1
-1 ** 2 (Fixnum) == 1
-1 ** 4611686018427387903 (Fixnum) == -1
-1 ** 4611686018427387904 (Bignum) == 1
-1 ** 4611686018427387905 (Bignum) == -1
-1 ** -1 (Fixnum) == -1/1
-1 ** -2 (Fixnum) == 1/1
-1 ** -4611686018427387904 (Fixnum) == 1/1
-1 ** -4611686018427387905 (Bignum) == 1.0 # Bug
-1 ** -4611686018427387906 (Bignum) == 1.0 # Bug
=end
--
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