Oh, you're so random - Speaker Deck

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select a random element

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select a random element ‘tis one is ok.

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Information Theory

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hard TOPIC Information Theory

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hard TOPIC dumb SPEAKER + Information Theory

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0≤H(X)≤1 where X is a discrete random variable

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0≤H(X)≤1 where X is a discrete random variable unpredictable

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0≤H(X)≤1 where X is a discrete random variable unpredictable always the same

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ask a question.

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bool is_random(char *bytes, size_t n) { }

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bool is_random(char *bytes, size_t n) { } AGHHH

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UNIFORM distribution

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UNIFORM distribution

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select a random element array[rand() % array.size]

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select a random element array[rand() % array.size] UNIFORM distribution

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select a random element array[rand() % array.size] UNIFORM distribution

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select a random element array[rand() % array.size] UNIFORM distribution AGHHH

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This is how you kill the RANDOM pnrg array

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This is how you kill the RANDOM a pnrg array

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This is how you kill the RANDOM a pnrg array

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This is how you kill the RANDOM a a pnrg array

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This is how you kill the RANDOM a a pnrg array

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This is how you kill the RANDOM a a a pnrg array

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This is how you kill the RANDOM a a a pnrg array

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This is how you kill the RANDOM a a a pnrg array

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This is how you kill the RANDOM a a a b pnrg array

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This is how you kill the RANDOM a a a b pnrg array

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This is how you kill the RANDOM a a a b b pnrg array

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This is how you kill the RANDOM a a a b b pnrg array

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This is how you kill the RANDOM a a a b b pnrg array

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This is how you kill the RANDOM a a a b b pnrg array

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how to FIX:

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how to FIX: 1. Random is hard

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how to FIX: 1. Random is hard 2. Run away

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how to FIX: 1. Random is hard 2. Run away Math.random() // between 0.0 and 1.0 Javascript

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how to FIX: 1. Random is hard 2. Run away

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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

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Good.

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Good. (but I don’t care)

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“PRNGs and Hash functions are in the same family of algorithms”

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hash tables out of nowhere!

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hash tables out of nowhere! O(1)

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hash tables out of nowhere! O(1) uniform

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pathological average data set: O(1)

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pathological average data set: O(1)

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pathological average data set: O(1) O(n)

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ONE fix

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ONE fix INT_MAX % size == 0

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collide make them

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collide make them • Brute force

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