Ruby modulo 3 with negative numbers is unintuitive -


ruby modulo rules negative numbers unclear. in irb: 

-7 % 3 == 2

should 1! why?

when 1 of operands % negative, there’s no clear best answer result return. every programming language has own rules. wikipedia page modulo operation has giant table of how each programming language has decided handle this, , there’s no clear consensus:

$ # modulus sign is: $ $ curl 'http://en.wikipedia.org/w/index.php?title=modulo_operation&action=edit&section=1' \     | egrep -o 'divisor|dividend|always positive|closest zero|not defined|implementation defined' \     | sort | uniq -c | sort -nr    67 dividend   42 divisor    7 positive    4 closest 0    2 not defined    2 implementation defined

some choose sign of left-hand operand, , right-hand operand. others don’t specify. example, the c programming language says:

the sign of result % [is] machine-dependent negative operands

instead of making particular choice how handle this, c returns whatever particular hardware or compiler being used have chosen implement! seems have been standardized in more recent versions of c programming language standards.

if want particular version in ruby, there 2 different methods call, modulo aka %, , remainder, different behaviour on negative numbers:

$ irb irb(main):001:0> -7.modulo(3) => 2 irb(main):002:0> -7.remainder(3) => -1

in other languages don’t have built-in methods this, may end using % twice desired sign.


Comments

Post a Comment

Popular posts from this blog

Why does Ruby on Rails generate add a blank line to the end of a file? -

running rails generate controller foo home results in: class foocontroller < application controller def home end end (there's nothing on line in actual file, blank line) is there purpose blank line? it's common use newline indicate end of line, last line. many editors (like vi, use) add in newline silently. consensus text files (especially in unix world) should end in newline, , there have been problems historically if wasn't present. why should text files end newline? the tool used count lines in file "wc" counts newlines in file, without trailing newline show 3 instead of 4. it improves readability of templates used in generator. consider: https://github.com/rails/rails/blob/master/railties/lib/rails/generators/rails/controller/templates/controller.rb to remove trailing newline, template have last line of: end<% end -%> instead of: end <% end -%> that seems less readable me. the discussion below refers ...
Read more

keyboard - Smiles and long press feature in Android -

i've created android keyboard. how add features inserting smilies, , using long keypresses display symbols? to create long-press behavior allows select several options pop-up menu, follow guide (specifically pop-up menu section): http://developer.android.com/guide/topics/ui/menus.html smileys (also known emoticons) combination of keys, understood programs , parsed same way. have do, when clicks smiley face on keyboard, simulate pressing of key combination matching emoticon. example, when clicks smiley, should simulate key presses ':' , ')' :). here's list of emoticons: http://en.wikipedia.org/wiki/list_of_emoticons
Read more

node.js - Bad Request - node js ajax post -

i'm using express 3.0 , node v0.11.0. have button submits form , i'm using ajax post data json object node server. client code is: $('#contact').submit(function(e) { console.log('submit called'); var formdata = json.stringify($('form').serializeobject()); console.log(formdata); $.ajax({ url: "http://localhost:3000/savedata/", type: "post", datatype: 'json', data: {objectdata: formdata}, contenttype: "application/json", complete: function() { console.log('process complete'); }, success: function(data) { console.log('process sucess'); }, error: function() { console.log('process error'); }, }); return false; }); then on server: var express = require('express'); var app = express(); app.set('views', __dirname + '/views'); app.set('view engine', 'jade'); app.use(express.bodyparser());...
Read more