From: ZyX <kp-pav@yandex.ru>
To: Vincent Lefevre <vincent@vinc17.net>,
"zsh-workers@zsh.org" <zsh-workers@zsh.org>
Subject: Re: Math expression evaluation error?
Date: Mon, 12 Jan 2015 19:18:22 +0300 [thread overview]
Message-ID: <1518701421079502@web12g.yandex.ru> (raw)
In-Reply-To: <20150112091737.GB27773@xvii.vinc17.org>
12.01.2015, 12:18, "Vincent Lefevre" <vincent@vinc17.net>:
> On 2015-01-10 21:10:16 -0800, Ray Andrews wrote:
>> Sure. That's the best argument for leaving it alone and of course it is
>> perfectly sound. I'd go the other way, liking friendliness more, but
>> I respect your decision. And I could be quite wrong about 1/2 + 1/2 = 0,
>> strange as it looks to me, rounding down could be vital to some code
>> somewhere.
>
> It's only a notation problem. Unfortunately / was chosen (historically,
> not by zsh) as the symbol for integer division. The shell expression
> 1/2 + 1/2 just means:
>
> integer_div(1,2) + integer_div(1,2)
>
> where integer_div is the integer division function, which gives 0.
> This is perfectly correct math.
It is not integer division. 1.0/2 and 1/2.0 will give the same result: 0.5. If you want to see language with operator for integer division check out Python-3: it has / for always-floating-point-unless-overridden and // for always-integral-unless-overridden (note: *not* integer (i.e. int type), having float on either side of // will result in floating-point integral value). Though as usual you can do anything you like in your own class, including `rm -rf ~` when trying to use division.
I would rather call it “type-specific division”. And I think that Python-3 way is least surprising and most convenient variant. Though you should not use // for dividing non-integral floats: 1.5//0.1 == 14.0 (rounding+decimal-binary conversion issues I guess).
>
> --
> Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
next prev parent reply other threads:[~2015-01-12 16:18 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-09 19:46 jdh
2015-01-09 20:15 ` Peter Stephenson
2015-01-09 21:40 ` jdh
2015-01-09 22:19 ` Ray Andrews
2015-01-09 23:06 ` Lawrence Velázquez
2015-01-09 23:52 ` Ray Andrews
2015-01-10 0:25 ` Bart Schaefer
2015-01-10 7:27 ` Ray Andrews
2015-01-10 16:53 ` Bart Schaefer
2015-01-10 18:48 ` Ray Andrews
2015-01-10 19:14 ` Bart Schaefer
2015-01-10 22:21 ` Ray Andrews
2015-01-11 1:51 ` Bart Schaefer
2015-01-11 5:10 ` Ray Andrews
2015-01-12 9:17 ` Vincent Lefevre
2015-01-12 16:18 ` ZyX [this message]
2015-01-13 16:00 ` Vincent Lefevre
2015-01-13 23:03 ` ZyX
2015-01-14 14:47 ` Vincent Lefevre
2015-01-14 21:37 ` ZyX
2015-01-15 13:34 ` Vincent Lefevre
2015-01-15 13:41 ` Vincent Lefevre
2015-01-15 18:32 ` ZyX
2015-01-15 21:57 ` Bart Schaefer
2015-01-09 22:40 ` Peter Stephenson
2015-01-12 10:55 ` Peter Stephenson
2015-01-14 15:02 ` Vincent Lefevre
2015-01-14 15:38 ` Peter Stephenson
2015-01-15 14:58 ` Peter Stephenson
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