Why does math.random(999999999999) returns 1 in Lua? -


i tried: print(math.random(999999999999)) , has printed 1.

also math.random() includes 999999999999 printing same thing. examples:

print(math.random(1.999999999999)) » 1

print(math.random(1999999999999)) » 1

for k,v in next,{math.random(999999999999), math.random(1999999999999), math.random(2.999999999999)}     print(v) end

» 1

local n = math.random(999999999999) print(n==1)

» true

then think understood (if know lua of course). can explain me?

@edits:

the lua version i'm using 5.2.

i tried print(math.random(-999999999999)) , printed 111711452. looks worked positive number.

this problem surely because math.random treats input arguments passed in lua 5.1 and/or 5.2. [mathlib.c]1:

as may know in c, standard int can represent values -2,147,483,648 2,147,483,647. adding +1 2,147,483,647, in use-case, overflow , wrap around value giving -2,147,483,648. end result negative since you're multiplying positive negative number.

there few ways rectify , handle problem:

  1. upgrade latest lua version 5.3 . 1 has since fixed issue treating input arguments lua_number instead.
  2. switch luajit not have integer overflow issue.
  3. patch lua 5.1 and/or 5.2 source fix , recompile.
  4. modify random range not overflow

and last query read documentation:http://lua-users.org/wiki/mathlibrarytutorial

notice last line quotes:

math.random(upper) generates integer numbers between 1 , upper.upper , lower must integer. in other case lua casts upper integer, giving math.floor(upper) , others math.ceil(upper), unexpected results (the same lower).


Comments

Post a Comment

Popular posts from this blog

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m...
Read more

python Tkinter Capturing keyboard events save as one single string -

is possible store keyboard events 1 string? code below stores 1 char , prints it. card reader or bar code reader, contains collection of character/ string not 1 character @ time. goal save char pressed text variable. from tkinter import * root = tk() def key(event): text= event.char text+= event.char print ("pressed", text) def callback(event): frame.focus_set() print ("clicked at", event.x, event.y) frame = frame(root, width=100, height=100) frame.bind("<key>", key) frame.bind("<button-1>", callback) frame.pack() root.mainloop() currently, creating text variable , everytime key() function gets called, , text stores last character typed. you can define text module level variable , , use module level text inside key function - text = '' def key(event): global text text+= event.char print("pressed", text)
Read more

sql server - Why does Linq-to-SQL add unnecessary COUNT()? -

here tables: create table customer ( cid int primary key, name varchar(32) ) create table ord ( oid int primary key, cid int foreign key references customer, address varchar(20) ) here's linq-to-sql statement: var aaa = c in db.customer select new { c, o = c.ord.tolist() }; and here's inexplicable query generated linq-to-sql: select [t0].[cid] [cid], [t0].[name] [name], [t1].[oid] [oid], [t1].[cid] [cid2], [t1].[address] [address], (select count(*) [dbo].[ord] [t2] [t2].[cid] = [t0].[cid]) [value] [dbo].[customer] [t0] left outer join [dbo].[ord] [t1] on [t1].[cid] = [t0].[cid] order [t0].[cid], [t1].[oid] i want understand how rid of count(*) part. it's entirely uncalled for! linq needs count(*) in order determine number of entries returned o = c.ord.tolist() .
Read more