From: "phasis68 (Heesob Park)" <phasis@...>
Date: 2012-09-06T18:19:37+09:00
Subject: [ruby-core:47448] [ruby-trunk - Bug #6986] Inconsistent result of BigDecimal#power


Issue #6986 has been updated by phasis68 (Heesob Park).


Could you try "p BigDecimal('1e-10').power(1e50)" ?
On Windows, the parameter higher than 1e19 returns Infinity instead of 0.0.


Here is a patch of NoMemoryError on Windows.

diff --git a/bigdecimal.c b/bigdecimal.c.new
index e798781..976503b 100644
--- a/bigdecimal.c
+++ b/bigdecimal.c.new
@@ -2184,7 +2184,7 @@ retry:
     if (exp != NULL) {
        return rmpd_power_by_big_decimal(x, exp, n);
     }
-    else if (TYPE(vexp) == T_BIGNUM) {
+    else if (TYPE(vexp) == T_BIGNUM || FIX2INT(vexp)>=10000000) {
        VALUE abs_value = BigDecimal_abs(self);
        if (is_one(abs_value)) {
            return ToValue(VpCreateRbObject(n, "1"));

----------------------------------------
Bug #6986: Inconsistent result of BigDecimal#power
https://bugs.ruby-lang.org/issues/6986#change-29206

Author: phasis68 (Heesob Park)
Status: Assigned
Priority: Normal
Assignee: mrkn (Kenta Murata)
Category: ext
Target version: 
ruby -v: ruby 2.0.0dev (2012-09-05 trunk 36913) [i386-mswin32_100]


I found BigDecimal#power returns incorrect result for a large value.

C:\tmp>ruby -rbigdecimal -e "p BigDecimal('1e-10').power(1e7)"
#<BigDecimal:a2bdb8,'0.1E-99999999',9(100000026)>

C:\tmp>ruby -rbigdecimal -e "p BigDecimal('1e-10').power(1e8)"
-e:1:in `power': failed to allocate memory (NoMemoryError)
        from -e:1:in `<main>'
	
C:\tmp>ruby -rbigdecimal -e "p BigDecimal('1e-10').power(1e10)"
#<BigDecimal:f7cb3c,'0.0',9(18)>

C:\tmp>ruby -rbigdecimal -e "p BigDecimal('1e-10').power(1e19)"
#<BigDecimal:f7cb3c,'Infinity',9(18)>




-- 
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