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math.c: Fix Math.log against huge bignum [Bug #19878]

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This commit is contained in:
Yusuke Endoh 2023-09-13 18:56:24 +09:00
parent 4655d2108e
commit 411572661a
Notes: git 2023-09-13 12:40:25 +00:00 
Merged: https://github.com/ruby/ruby/pull/8429
2 changed files with 3 additions and 2 deletions
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4
math.c
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@ -561,14 +561,14 @@ rb_math_log(int argc, const VALUE *argv)
return DBL2NUM(-0.0); return DBL2NUM(-0.0);
} }
d = log_intermediate(d) / log_intermediate(b); d = log_intermediate(d) / log_intermediate(b);
numbits -= numbits_2; d += (numbits - numbits_2) * M_LN2 / log(b);
} }
else { else {
/* check for pole error */ /* check for pole error */
if (d == 0.0) return DBL2NUM(-HUGE_VAL); if (d == 0.0) return DBL2NUM(-HUGE_VAL);
d = log(d); d = log(d);
}
d += numbits * M_LN2; d += numbits * M_LN2;
}
return DBL2NUM(d); return DBL2NUM(d);
} }

1
test/ruby/test_math.rb
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@ -168,6 +168,7 @@ class TestMath < Test::Unit::TestCase
assert_nothing_raised { assert_nan(Math.log(1.0, Float::NAN)) } assert_nothing_raised { assert_nan(Math.log(1.0, Float::NAN)) }
assert_nothing_raised { assert_infinity(-Math.log(0)) } assert_nothing_raised { assert_infinity(-Math.log(0)) }
assert_nothing_raised { assert_infinity(-Math.log(0, 2)) } assert_nothing_raised { assert_infinity(-Math.log(0, 2)) }
check(307.95368556425274, Math.log(2**1023, 10))
end end
def test_log2 def test_log2