Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Oh, you're so random
Search
Vicent Martí
March 25, 2012
Programming
14
2.5k
Oh, you're so random
Randomness and pink ponies in Codemotion Rome 2012
Vicent Martí
March 25, 2012
Tweet
Share
More Decks by Vicent Martí
See All by Vicent Martí
Unicorns Die With Bullets Made of Glitter
tanoku
5
520
Threedee Tales From Urban Bohemia
tanoku
2
770
My Mom told me that Git doesn't scale
tanoku
28
1.8k
Intergalactic Javascript Robots from Outer Space
tanoku
270
27k
Ruby is Unlike a Banana
tanoku
97
11k
A talk about libgit2
tanoku
11
1.6k
Other Decks in Programming
See All in Programming
SwiftUI API Design Lessons
niw
1
260
Java 24まとめ / Java 24 summary
kishida
3
490
Kamal 2 – Get Out of the Cloud
aleksandrov
1
180
Go1.24 go vetとtestsアナライザ
kuro_kurorrr
2
840
Going Structural with Named Tuples
bishabosha
0
200
Strategic Design (DDD)for the Frontend @DDD Meetup Stuttgart
manfredsteyer
PRO
0
110
「”誤った使い方をすることが困難”な設計」で良いコードの基礎を固めよう / phpcon-odawara-2025
taniguhey
0
120
Agentic Applications with Symfony
el_stoffel
2
270
英語 × の私が、生成AIの力を借りて、OSSに初コントリビュートした話
personabb
0
190
自分のために作ったアプリが、グローバルに使われるまで / Indie App Development Lunch LT
pixyzehn
1
150
「影響が少ない」を自分の目でみてみる
o0h
PRO
2
1k
Enterprise Web App. Development (1): Build Tool Training Ver. 5
knakagawa
1
110
Featured
See All Featured
Visualization
eitanlees
146
16k
[RailsConf 2023 Opening Keynote] The Magic of Rails
eileencodes
29
9.4k
Helping Users Find Their Own Way: Creating Modern Search Experiences
danielanewman
29
2.5k
Git: the NoSQL Database
bkeepers
PRO
430
65k
Principles of Awesome APIs and How to Build Them.
keavy
126
17k
Let's Do A Bunch of Simple Stuff to Make Websites Faster
chriscoyier
507
140k
jQuery: Nuts, Bolts and Bling
dougneiner
63
7.7k
Refactoring Trust on Your Teams (GOTO; Chicago 2020)
rmw
34
2.9k
GraphQLの誤解/rethinking-graphql
sonatard
71
10k
Being A Developer After 40
akosma
91
590k
The Cost Of JavaScript in 2023
addyosmani
49
7.7k
The Myth of the Modular Monolith - Day 2 Keynote - Rails World 2024
eileencodes
23
2.6k
Transcript
None
select a random element
select a random element ‘tis one is ok.
None
None
Information Theory
hard TOPIC Information Theory
hard TOPIC dumb SPEAKER + Information Theory
0≤H(X)≤1 where X is a discrete random variable
0≤H(X)≤1 where X is a discrete random variable unpredictable
0≤H(X)≤1 where X is a discrete random variable unpredictable always
the same
None
ask a question.
None
bool is_random(char *bytes, size_t n) { }
bool is_random(char *bytes, size_t n) { } AGHHH
UNIFORM distribution
UNIFORM distribution
select a random element array[rand() % array.size]
select a random element array[rand() % array.size] UNIFORM distribution
select a random element array[rand() % array.size] UNIFORM distribution
select a random element array[rand() % array.size] UNIFORM distribution AGHHH
This is how you kill the RANDOM pnrg array
This is how you kill the RANDOM a pnrg array
This is how you kill the RANDOM a pnrg array
This is how you kill the RANDOM a a pnrg
array
This is how you kill the RANDOM a a pnrg
array
This is how you kill the RANDOM a a a
pnrg array
This is how you kill the RANDOM a a a
pnrg array
This is how you kill the RANDOM a a a
pnrg array
This is how you kill the RANDOM a a a
b pnrg array
This is how you kill the RANDOM a a a
b pnrg array
This is how you kill the RANDOM a a a
b b pnrg array
This is how you kill the RANDOM a a a
b b pnrg array
This is how you kill the RANDOM a a a
b b pnrg array
This is how you kill the RANDOM a a a
b b pnrg array
how to FIX:
how to FIX: 1. Random is hard
how to FIX: 1. Random is hard 2. Run away
how to FIX: 1. Random is hard 2. Run away
Math.random() // between 0.0 and 1.0 Javascript
how to FIX: 1. Random is hard 2. Run away
how to FIX: 1. Random is hard 2. Run away
prng.rand(5..9) #=> one of [5, 6, 7, 8, 9] prng.rand(5...9) #=> one of [5, 6, 7, 8] Ruby
Good.
Good. (but I don’t care)
None
“PRNGs and Hash functions are in the same family of
algorithms”
None
hash tables out of nowhere!
hash tables out of nowhere! O(1)
hash tables out of nowhere! O(1) uniform
pathological average data set: O(1)
pathological average data set: O(1)
pathological average data set: O(1) O(n)
ONE fix
ONE fix INT_MAX % size == 0
collide make them
collide make them • Brute force
collide make them • Brute force • MITM
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
problem & that’s a
problem & that’s a painful comparisons
problem & that’s a painful comparisons ~700ms responses
MANY fixes
MANY fixes (but only one is right)
MANY fixes (but only one is right) 1. Limiting request
size
this is bad and you should feel bad! MANY fixes
(but only one is right) 1. Limiting request size
MANY fixes (but only one is right) 2. Changing the
hash table
MANY fixes (but only one is right) 2. Changing the
hash table (no comment)
MANY fixes (but only one is right) 3. Bring back
the random
None
“Randomness is too important to be left to chance”
Thanks. “Randomness is too important to be left to chance”