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numeric.c: Fix round_half_even for specific values (#7023)

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Handle the integert and the float parts separately in round_half_even
to prevent error occursions in floating point calculation.
This commit is contained in:
Kenta Murata 2022-12-26 21:02:47 +09:00 committed by GitHub
parent bb60e4615f
commit 9f2378959e
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GPG Key ID: 4AEE18F83AFDEB23
Notes: git 2022-12-26 12:03:08 +00:00 
Merged-By: mrkn <mrkn@ruby-lang.org>
3 changed files with 28 additions and 11 deletions
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26
numeric.c
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@ -144,31 +144,37 @@ round_half_down(double x, double s)
static double static double
round_half_even(double x, double s) round_half_even(double x, double s)
{ {
double f, d, xs = x * s; double u, v, us, vs, f, d, uf;
v = modf(x, &u);
us = u * s;
vs = v * s;
if (x > 0.0) { if (x > 0.0) {
f = floor(xs); f = floor(vs);
d = xs - f; uf = us + f;
d = vs - f;
if (d > 0.5) if (d > 0.5)
d = 1.0; d = 1.0;
else if (d == 0.5 || ((double)((f + 0.5) / s) <= x)) else if (d == 0.5 || ((double)((uf + 0.5) / s) <= x))
d = fmod(f, 2.0); d = fmod(uf, 2.0);
else else
d = 0.0; d = 0.0;
x = f + d; x = f + d;
} }
else if (x < 0.0) { else if (x < 0.0) {
f = ceil(xs); f = ceil(vs);
d = f - xs; uf = us + f;
d = f - vs;
if (d > 0.5) if (d > 0.5)
d = 1.0; d = 1.0;
else if (d == 0.5 || ((double)((f - 0.5) / s) >= x)) else if (d == 0.5 || ((double)((uf - 0.5) / s) >= x))
d = fmod(-f, 2.0); d = fmod(-uf, 2.0);
else else
d = 0.0; d = 0.0;
x = f - d; x = f - d;
} }
return x; return us + x;
} }
static VALUE fix_lshift(long, unsigned long); static VALUE fix_lshift(long, unsigned long);

2
spec/ruby/core/float/round_spec.rb
View File

@ -136,7 +136,7 @@ describe "Float#round" do
-4.809999999999999.round(5, half: :even).should eql(-4.81) -4.809999999999999.round(5, half: :even).should eql(-4.81)
end end
ruby_bug "", ""..."3.4" do ruby_bug "", ""..."3.3" do
# These numbers are neighbouring floating point numbers round a # These numbers are neighbouring floating point numbers round a
# precise value. They test that the rounding modes work correctly # precise value. They test that the rounding modes work correctly
# round that value and precision is not lost which might cause # round that value and precision is not lost which might cause

11
test/ruby/test_float.rb
View File

@ -486,6 +486,17 @@ class TestFloat < Test::Unit::TestCase
assert_equal(-1.26, -1.255.round(2)) assert_equal(-1.26, -1.255.round(2))
end end
def test_round_half_even_with_precision
assert_equal(767573.18759, 767573.1875850001.round(5, half: :even))
assert_equal(767573.18758, 767573.187585.round(5, half: :even))
assert_equal(767573.18758, 767573.1875849998.round(5, half: :even))
assert_equal(767573.18758, 767573.187575.round(5, half: :even))
assert_equal(-767573.18759, -767573.1875850001.round(5, half: :even))
assert_equal(-767573.18758, -767573.187585.round(5, half: :even))
assert_equal(-767573.18758, -767573.1875849998.round(5, half: :even))
assert_equal(-767573.18758, -767573.187575.round(5, half: :even))
end
def test_floor_with_precision def test_floor_with_precision
assert_equal(+0.0, +0.001.floor(1)) assert_equal(+0.0, +0.001.floor(1))
assert_equal(-0.1, -0.001.floor(1)) assert_equal(-0.1, -0.001.floor(1))