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* ext/bigdecimal/lib/bigdecimal/math.rb (atan): atan(Infinity) is

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PI/2.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@25063 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
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nobu 2009-09-23 17:21:26 +00:00
parent 1ef3ac4738
commit 39ea1c8c7c
3 changed files with 13 additions and 15 deletions
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5
ChangeLog
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@ -1,4 +1,7 @@
Thu Sep 24 02:08:35 2009 Nobuyoshi Nakada <nobu@ruby-lang.org> Thu Sep 24 02:21:23 2009 Nobuyoshi Nakada <nobu@ruby-lang.org>
* ext/bigdecimal/lib/bigdecimal/math.rb (atan): atan(Infinity) is
PI/2.
* ext/bigdecimal/lib/bigdecimal/math.rb (atan): reduce loop with * ext/bigdecimal/lib/bigdecimal/math.rb (atan): reduce loop with
the formula of the double corner. based on a patch from the formula of the double corner. based on a patch from

20
ext/bigdecimal/lib/bigdecimal/math.rb
View file

@ -117,22 +117,16 @@ module BigMath
# Computes the arctangent of x to the specified number of digits of precision. # Computes the arctangent of x to the specified number of digits of precision.
# #
# If x is infinite or NaN, returns NaN. # If x is NaN, returns NaN.
def atan(x, prec) def atan(x, prec)
raise ArgumentError, "Zero or negative precision for atan" if prec <= 0 raise ArgumentError, "Zero or negative precision for atan" if prec <= 0
return BigDecimal("NaN") if x.infinite? || x.nan? return BigDecimal("NaN") if x.nan?
pi = PI(prec) pi = PI(prec)
if neg = x < 0 x = -x if neg = x < 0
x = -x return pi.div(neg ? -2 : 2, prec) if x.infinite?
end return pi / (neg ? -4 : 4) if x.round(prec) == 1
if x.round(prec) == 1 x = 1 / x if inv = x > 1
return pi / (neg ? -4 : 4) x = (-1 + sqrt(1 + x**2, prec))/x if dbl = x > 0.5
elsif inv = x > 1
x = 1 / x
end
if dbl = x > 0.5
x = (-1 + sqrt(1 + x**2, prec))/x
end
n = prec + BigDecimal.double_fig n = prec + BigDecimal.double_fig
y = x y = x
d = y d = y

3
test/bigdecimal/test_bigmath.rb
View file

@ -21,7 +21,7 @@ class TestBigMath < Test::Unit::TestCase
assert_equal(0.0, sqrt(BigDecimal("-0"), N)) assert_equal(0.0, sqrt(BigDecimal("-0"), N))
assert_raise(FloatDomainError) {sqrt(BigDecimal("-1.0"), N)} assert_raise(FloatDomainError) {sqrt(BigDecimal("-1.0"), N)}
assert_raise(FloatDomainError) {sqrt(NAN, N)} assert_raise(FloatDomainError) {sqrt(NAN, N)}
assert_equal(PINF, sqrt(PINF, N)) assert_raise(FloatDomainError) {sqrt(PINF, N)}
end end
def test_sin def test_sin
@ -56,6 +56,7 @@ class TestBigMath < Test::Unit::TestCase
assert_equal(0.0, atan(BigDecimal("0.0"), N)) assert_equal(0.0, atan(BigDecimal("0.0"), N))
assert_in_delta(Math::PI/4, atan(BigDecimal("1.0"), N)) assert_in_delta(Math::PI/4, atan(BigDecimal("1.0"), N))
assert_in_delta(Math::PI/6, atan(sqrt(BigDecimal("3.0"), N) / 3, N)) assert_in_delta(Math::PI/6, atan(sqrt(BigDecimal("3.0"), N) / 3, N))
assert_in_delta(Math::PI/2, atan(PINF, N))
end end
def test_exp def test_exp