# \[Bug:1.9\] exact Time and inexact Time

**URL:** <https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934>\
**Category:** Development\
**Created:** [May 14, 2009, 6:52am UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934 "2009-05-14T06:52:56Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [May 14, 2009, 6:52am UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934/1 "2009-05-14T06:52:56Z")

</div>

e$B1sF#$G$9!#e(B

e$B8=:\_!"e(BTime#- e$B$,e(B Rational e$B$rJV$9$h$&$K$J$C$F$$$^$9!#e(B

$ ./ruby -e ‘p Time.now - Time.now’  
(-7/156250)

e$B$7$+$7!"e(BTime.now e$B$N$h$&$Ke(B inexact  
e$B$J;~9o$N:9J,$,!"e(Bexact e$B$Ne(B  
e$B$h$&$K8+$($ke(B Rational e$B$K$J$k$N$O$h$/$J$$$H;W$$$^$9!#e(B

Time.gm(2000) e$B$J$I$Oe(B exact e$B$J;~9o$H9M$($i$l$^$9$,!"$=$l$G$be(B  
e$B0J2\<$Ge(B Rational e$B$,JV$k$N$O9%$^$7$/$J$$$H;W$$$^$9!#e(B

$ ./ruby -e ‘p Time.gm(2000) + 0.1 - Time.gm(2000)’  
(3602879701896397/36028797018963968)

e$B$h$C$Fe(B Time e$B%\*%V%8%’%/%H$Ke(B exact  
e$B$+$I$&$+$r$"$i$o$9%U%i%0$re(B  
e$B;}$?$;$kI,MW$,$"$k$N$G$O$J$$$G$7$g$&$+!#e(B

e$B$?$@!"e(BTime#- e$B$,e(B Rational  
e$B$rJV$7$F$b$h$$$H;W$o$l$kNc$O!"e(B

$ ./ruby -e ‘p Time.gm(2000) + Rational(1, 2) - Time.gm(2000)’  
(1/2)

e$B$/$i$$$7$+;W$$$D$-$^$;$s!#$J$N$Ge(B Time#- e$B$N7k2L$r\>o$Ke(B Integer  
e$B$^$?$Oe(B Float e$B$K$9$k$H$$$&A\*Br$b$"$k$+$b$7$l$^$;$s!#e(B

e$B$H$j$"$($:LdBjDs5/$HDs0F$G$9!#$I$&;W$o$l$^$9$G$7$g$&!#e(B

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [May 14, 2009, 5:01pm UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934/2 "2009-05-14T17:01:17Z")

</div>

In article  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid),  
Yusuke ENDOH [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

> e$B8=:\_!"e(BTime#- e$B$,e(B Rational e$B$rJV$9$h$&$K$J$C$F$$$^$9!#e(B
> 
> $ ./ruby -e ‘p Time.now - Time.now’  
> (-7/156250)
> 
> e$B$7$+$7!"e(BTime.now e$B$N$h$&$Ke(B inexact e$B$J;~9o$N:9J,$,!"e(Bexact e$B$Ne(B  
> e$B$h$&$K8+$($ke(B Rational e$B$K$J$k$N$O$h$/$J$$$H;W$$$^$9!#e(B

e$B0lHL$K?tCM7W;;$G$O!“CM$,;}$D8m:9$h$j$b=\<J,$K9b$$@:EY$r;}$C$Fe(B  
e$B$$$k?tCMI=8=$r;H$&I,MW$,$”$k$s$8$c$J$$$G$7$g$&$+!#e(B

e$B$?$H$($P!"Hf3SE_C;$$;~4V$r07$&MQES$G$O!"e(Bdouble e$B$OBEEv$JA_Bre(B  
e$B;h$+$b$7$l$^$;$s!#e(B

e$B$7$+$7!“0[$J$ke(B Epoch e$B$XJQ49$9$k$H$$$&MQES$G$Oe(B double  
e$B$G$O=\<e(B  
e$BJ,$G$J$$$3$H$b$”$k$G$7$g$&!#e(B

e$B$I$A$i$be(B Time e$BF1;N$N0z$-;;$G\<B8=$G$-$^$9$,!"I,MW$J@:EY$O0[$Je(B  
e$B$j$^$9!#e(B

e$B$A$J$\_$K!“e(BUnix Epoch e$B$+$i%J%NICC10L$G?t$($k$H!”:#$N;~9o$Oe(B  
double e$B$G2\<$N$[$&$N%S%C%H$rI=8=$G$-$^$;$s!#$J$N$G!“e(Bdouble e$B7Pe(B  
e$BM3$GB\>$Ne(B Epoch e$B$KJQ49$7$F!“JQ49$7$?B&$G7W;;$9$k$H!”@:EY$,Mne(B  
e$B$A$F$$$FE,@Z$JCM$K$J$i$J$$!”$H$$$&2DG=@-$b$"$j$^$9!#$^$!!"6qe(B  
e$BBNE\*$Je(B Epoch e$B$HJQ49$N$d$j$+$?$K$b$h$j$^$9$,!#e(B

inexact, exact e$B$H$$$&C1=c$J6hJL$G$O$J$/$F!“MQK!$K$h$C$F$I$Ne(B  
e$B$/$i$$$N8m:9$,5vMF$G$-$k$+!”$H$$$&E@$r5DO@$9$kI,MW$,$"$k$N$Ge(B  
e$B$O$J$$$G$7$g$&$+!#e(B

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [May 14, 2009, 6:13pm UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934/3 "2009-05-14T18:13:29Z")

</div>

卜部です。

Tanaka A. さんは書きました:

> 一般に数値計算では、値が持つ誤差よりも充分に高い精度を持って  
> いる数値表現を使う必要があるんじゃないでしょうか。

無闇矢鱈に高けりゃいいってもんでもないはずです。

たとえばRationalは無限に高い精度を持つものと考えるのが一般的であると思います。  
すると、もしTime.nowが誤差を含んでいるのだとしたら、それをRationalで表現すると  
ã€Œèª¤å·®ã‚’å«ã‚“ã§ã„ã‚‹ã€ã¨ã„ã†æƒ…å ±ã‚’å¤±ã„ã¾ã™ã®ã§ã€Rationalは不適切です。

どのぐらいの誤差を許容できるかが用法によって異なるのに本気で取り組む気があるな  
ã‚‰ã€ãã¡ã‚“ã¨èª¤å·®ã‚’æ‰±ãˆã‚‹ãƒ‡ãƒ¼ã‚¿æ§‹é€ ã€ãŸã¨ãˆã°BigDecimalなどを採用すべきだと思い  
ます。

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [May 15, 2009, 1:50pm UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934/4 "2009-05-15T13:50:16Z")

</div>

e$B1sF#$G$9!#e(B

2009/05/15 0:00 Tanaka A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> e$B0lHL$K?tCM7W;;$G$O!“CM$,;}$D8m:9$h$j$b=\<J,$K9b$$@:EY$r;}$C$Fe(B  
> e$B$$$k?tCMI=8=$r;H$&I,MW$,$”$k$s$8$c$J$$$G$7$g$&$+!#e(B

e$B?tCM7W;;$NLdBj$b$“$k$+$b$7$l$^$;$s$,!”;d$O%$%s%?!\<%U%'%$%9$Ne(B  
e$BLdBj$r5$$K$7$F$$$^$9!#e(B

e$BKNIt$5$s$b$\*$C$7$c$C$F$$$^$9$,!“e(BRational  
e$B$O!V8m:9$,$J$$?tCM!W$re(B  
e$BI=8=$7$F$$$k$h$&$K$7$+8+$($:!”!V==J,$K9b$$@:EY$r;}$C$F$$$k?tCM!We(B  
e$B$H$7$F;H$o$l$F$$$k$H$O9M$(IU$-$^$;$s!#e(B

e$B$=$N$?$a!“:GDc$G$be(B Float e$B$+$ie(B Rational  
e$B$K0EL[$KJQ49$5$l$k$3$H$,e(B  
e$B$”$k$N$O!"2?$i$+$N=hCV$r$9$Y$-LdBj$@$H;W$$$^$9!#6qBNE\*$JJ}K!$Oe(B  
e$B$H$b$+$/!#e(B

> e$B$7$+$7!“0[$J$ke(B Epoch e$B$XJQ49$9$k$H$$$&MQES$G$Oe(B double e$B$G$O=\<e(B  
> e$BJ,$G$J$$$3$H$b$”$k$G$7$g$&!#e(B
> 
> e$B$I$A$i$be(B Time e$BF1;N$N0z$-;;$G\<B8=$G$-$^$9$,!"I,MW$J@:EY$O0[$Je(B  
> e$B$j$^$9!#e(B

e$B$$$m$$$m9M$($?$s$G$9$,!"e(BTime#to\_r e$B$rMQ0U$7$?$i$I$&$G$7$g$&!#e(B  
e$B8m:9$J$/e(B Epoch e$BJQ49$7$?$$?M$O!"e(Bto\_r e$B$7$F@53N$Je(B Unix  
Epoch e$B$Ke(B  
e$B$7$F$+$i!"e(BTime e$B$G$J$/e(B Rational  
e$B$G$d$C$F$/$l$H$$$&$3$H$G!#e(B

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [May 17, 2009, 2:46pm UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934/5 "2009-05-17T14:46:39Z")

</div>

In article [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid),  
Yusuke ENDOH [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

> e$B$$$m$$$m9M$($?$s$G$9$,!"e(BTime#to\_r e$B$rMQ0U$7$?$i$I$&$G$7$g$&!#e(B  
> e$B8m:9$J$/e(B Epoch e$BJQ49$7$?$$?M$O!"e(Bto\_r e$B$7$F@53N$Je(B Unix Epoch e$B$Ke(B  
> e$B$7$F$+$i!"e(BTime e$B$G$J$/e(B Rational e$B$G$d$C$F$/$l$H$$$&$3$H$G!#e(B

Time#to\_r e$B$r2C$($k$N$O$"$jF@$k$H;W$$$^$9!#e(B

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [May 18, 2009, 2:06am UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934/6 "2009-05-18T02:06:17Z")

</div>

e$B$^$D$b$He(B e$B$f$-$R$m$G$9e(B

In message “Re: [ruby-dev:38484] Re: [Bug:1.9] exact Time and inexact  
Time”  
on Sun, 17 May 2009 21:46:01 +0900, Tanaka A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
writes:

|Time#to\_r e$B$r2C$($k$N$O$"$jF@$k$H;W$$$^$9!#e(B

e$B;d$b$3$A$i$K;?@.$7$^$9!#e(B

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [May 18, 2009, 6:03pm UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934/7 "2009-05-18T18:03:56Z")

</div>

e$B1sF#$G$9!#e(B

2009/05/18 9:05 Yukihiro M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> e$B$^$D$b$He(B e$B$f$-$R$m$G$9e(B
> 
> In message “Re: [ruby-dev:38484] Re: [Bug:1.9] exact Time and inexact Time”  
> on Sun, 17 May 2009 21:46:01 +0900, Tanaka A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:
> 
> |Time#to\_r e$B$r2C$($k$N$O$"$jF@$k$H;W$$$^$9!#e(B
> 
> e$B;d$b$3$A$i$K;?@.$7$^$9!#e(B

e$B$=$l$G$O%Q%C%A$r=q$-$^$7$?!#e(B

- Time#to\_r e$B$rDI2Ce(B
- Time#- e$B$O\>o$Ke(B Float e$B$rJV$9e(B (1.9.1 e$B$HF1$85sF0e(B)

e$BFC$KH?BP$,$J$1$l$P%3%\_%C%H$7$h$&$H;W$$$^$9!#e(B

# Index: time.c

— time.c (revision 23485)  
+++ time.c (working copy)  
@@ -2277,6 +2277,30 @@

/\*

- call-seq:

- 
  - 

```
time.to_r => Rational

```

- 
  - 

- 
  - Returns the value of _time_ as a rational number of seconds

- 
  - since the Epoch.

- 
  - 

- 
  - 

```
t = Time.now

```

- 
  - 

```
p t.to_r #=> (8807170717088293/8388608)

```

- 
  - 

- 
  - This method is intended to be used to get an accurate value

- 
  - representing nanoseconds from the Epoch. You can use this

- 
  - to convert time to another Epoch.

- \*/
- 

+static VALUE  
+time\_to\_r(VALUE time)  
+{

- struct time\_object \*tobj;
- 
- GetTimeval(time, tobj);
- return tobj-\>timev;  
+}
- 

+/\*

- 
  - call-seq:
  - 

```
time.usec => int

```

  - 

```
time.tv_usec => int

```

  - 

@@ -2803,7 +2827,7 @@  
struct time\_object \*tobj2;

GetTimeval(time2, tobj2);

- 

```
   return sub(tobj->timev, tobj2->timev);

```

- 

```
   return rb_Float(sub(tobj->timev, tobj2->timev));

```

}  
return time\_add(tobj, time2, -1);  
}  
@@ -3682,6 +3706,7 @@

rb\_define\_method(rb\_cTime, “to\_i”, time\_to\_i, 0);  
rb\_define\_method(rb\_cTime, “to\_f”, time\_to\_f, 0);

- rb\_define\_method(rb\_cTime, “to\_r”, time\_to\_r, 0);  
rb\_define\_method(rb\_cTime, “\<=\>”, time\_cmp, 1);  
rb\_define\_method(rb\_cTime, “eql?”, time\_eql, 1);  
rb\_define\_method(rb\_cTime, “hash”, time\_hash, 0);

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [May 21, 2009, 9:18pm UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934/8 "2009-05-21T21:18:36Z")

</div>

e$B%A%1%C%He(B #1481 e$B$,99?7$5$l$^$7$?!#e(B (by Yukihiro M.)

e$B%9%F!\<%?%9e(B Opene$B$+$ie(BClosede$B$KJQ99e(B  
ruby -v 1.9.1e$B$K%;%C%He(B

## redundant

[http://redmine.ruby-lang.org/issues/show/1481](http://redmine.ruby-lang.org/issues/show/1481)

---

<div class="post-metadata">

**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\
**Post date:** [May 19, 2009, 4:08pm UTC](https://www.ruby-forum.com/t/bug-1-9-exact-time-and-inexact-time/167934/9 "2009-05-19T16:08:14Z")

</div>

e$B%A%1%C%He(B #1468 e$B$,99?7$5$l$^$7$?!#e(B (by Yusuke E.)

e$B%9%F!\<%?%9e(B Opene$B$+$ie(BClosede$B$KJQ99e(B  
e$B?JD=e(B % 0e$B$+$ie(B100e$B$KJQ99e(B

## Applied in changeset r23490.

[http://redmine.ruby-lang.org/issues/show/1468](http://redmine.ruby-lang.org/issues/show/1468)