Bug #6862: BigMath.exp negative exponent

• Status: Closed
• Assignee: mrkn (Kenta Murata)
• Target version: 2.6
• ruby -v: ruby 1.9.3p260 (2012-08-09 revision 36669) [i686-linux]
• Backport: 1.9.3: DONE, 2.0.0: DONE

[karatedog (Földes László)]

Ruby 1.9.3 BigMath.exp accepts Fixnum for exponent but silently treats negative exponents as positive:
1.9.3p260 :009 > BigMath.exp(3, 10)
=> #BigDecimal:9be2ce8,'0.2008553692E2',18(72)
1.9.3p260 :010 > BigMath.exp(-3, 10)
=> #BigDecimal:9bd8e50,'0.2008553692E2',18(45)

Converting the exponent parameter to BigDecimal solves the problem:
1.9.3p260 :011 > BigMath.exp(BigDecimal(-3), 10)
=> #BigDecimal:9bd1420,'0.4978706837E-1',18(45)

[phasis68 (Heesob Park)]

BigMath.exp cannot handle floating point value too.

C:\Users\phasis>ruby -rbigdecimal -e 'p BigMath.exp(3.0,10)'
-e:1:in exp': Float can't be coerced into BigDecimal without a precision (ArgumentError) from -e:1:in '

And Here is a patch.

diff --git a/bigdecimal.c b/bigdecimal.c.new
index 866ce34..f0dc9bd 100644
--- a/bigdecimal.c
+++ b/bigdecimal.c.new
@@ -2546,6 +2546,7 @@ BigMath_s_exp(VALUE klass, VALUE x, VALUE vprec)
if (negative) {
VpSetSign(vx, 1);
}

• x = ToValue(vx);

  RB_GC_GUARD(one) = ToValue(VpCreateRbObject(1, "1"));
  RB_GC_GUARD(x1) = one;

[naruse (Yui NARUSE)]

• Status changed from Open to Assigned
• Assignee set to mrkn (Kenta Murata)

[naruse (Yui NARUSE)]

• Target version changed from 1.9.3 to 2.6

[phasis68 (Heesob Park)]

This issue was solved with changeset r41623.
BTW, my patch is same to Garth Snyder's and it is 11 months old.

[nagachika (Tomoyuki Chikanaga)]

• Backport set to 1.9.3: REQUIRED, 2.0.0: REQUIRED

[mrkn (Kenta Murata)]

• Status changed from Assigned to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r41723.
Földes, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

Additionally mention Heesob Park for his patch to [Bug #6862]

[mrkn (Kenta Murata)]

phasis68 (Heesob Park) wrote:

This issue was solved with changeset r41623.
BTW, my patch is same to Garth Snyder's and it is 11 months old.

I'm sorry I missed this issue and your patch.
I added your name in ChangeLog at r41723.

[mame (Yusuke Endoh)]

So phasis68 should have a commit bit, as I said. ;-)

--
Yusuke Endoh [e-mail]

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 1.9.3: REQUIRED, 2.0.0: REQUIRED to 1.9.3: REQUIRED, 2.0.0: DONE

[mrkn (Kenta Murata)]

mame (Yusuke Endoh) wrote:

So phasis68 should have a commit bit, as I said. ;-)

+1

[usa (Usaku NAKAMURA)]

• Backport changed from 1.9.3: REQUIRED, 2.0.0: DONE to 1.9.3: DONE, 2.0.0: DONE