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Questions tagged [reversible-computing]

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Can you unwind a cryptographic hash function's last round?

Given a cryptographic hash, $ \text{hash}(A || B || C) $, and the last block added to the hash, $ C $, can you determine $ \text{hash}(A || B) $? In other words, can you roll back the last round of a ...
Zaz's user avatar
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Prove that it is impossible to construct the toffoli gate using only CNOT gates

Show that it is not possible to construct the toffoli gate using only CNOT gates, given we are allowed to choose any number of ancilla bits. My Attempt The action of a toffoli gate can be defined as, ...
Sooraj S's user avatar
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Reversible computing as a path to a useful PRNG or hash function?

There's a question I've long had about reversible computing: do non-trivial algorithms usually end up generating strongly pseudorandom data as an artifact of the computation? The most straightforward ...
Trev's user avatar
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Are there any formal systems or programming languages in which its only possible to define functions that have inverses?

Consider an algorithm $f(x)$. Are there formal systems or programming languages that only allow $f(x)$ to be defined if $f^-1(x)$ exists?
newlogic's user avatar
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How does the circuit depth of a bijective function change if it is optimally rexpressed in terms of larger gates?

Consider a bijective function $f:\{0,1\}^n\rightarrow \{0,1\}^n$. Let $d_k$ be the minimal circuit depth of $f$ when expressed in terms of arbitrary $k$ bit gates (i.e. arbitrary bijective functions ...
Kfir Dolev's user avatar
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Would all objects in a reversible computing language be mutable?

Full disclosure, I'm asking this after watching a couple pop science videos; I do not know anything about the actual physics and hardware. I suspect the presenters expected an audience like me because ...
BatWannaBe's user avatar
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Is this statistical group summation unambiguously reversible?

Let $X$ be a finite multisubset of $\mathbb{N}^2$. Let's introduce the following notation: $A$ is a set of all first elements of pairs from $X$ and $B$ is a set of all second elements of pairs from $X$...
Tobias Hermann's user avatar
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Why isn't energy wasted with reversible computing? Isn't information discarded when we feed the function with a new input?

I understand that irreversible computing consumes energy because it has to "get rid" of outputs which have been used. With reversible computing that information is not "wasted" because with the ...
Nicu Righeriu's user avatar
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How to Implement a reversible OR operator with a Fredkin gate (controlled swap)?

How to implement a reversible OR operator with a Fredkin gate ?
Lokesh Pathak's user avatar
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What is the relation between reversible circuits and invertible functions?

A reversible circuit, if I understand it correctly, is a circuit where every gate in the circuit is invertible, i.e. can simply be “turned in the opposite direction”, so that the entire circuit can in ...
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How Janus (Reversible Programming Language) `if`, `while`, and Update Work

In Reversible Computing, all program statements are reversible. I understand for example that the following: \begin{align} x\ {+}&{=}\ 4\\ y\ {*}&{=}\ x\\ x\ {-}&{=}\ 10 \end{align} Has ...
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Reversible computation and no cloning theorem in quantum computing

I am having a problem in understanding a conflict between reversibility in quantum computation and the No cloning theorem. Given a function f, we construct the reversible version of f by adding ...
acevik's user avatar
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How to prove Landauer's principle [closed]

I have some questions about energy emitted when one bit of information is processed. Landauer's principle states the minimum possible amount of energy required to erase one bit of information is <...
Onur A.'s user avatar
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How to model reversible interactive programs

Reversible programs with finite execution steps are well studied. For example, a Turing machine whose transitions are reversible and halts can be executed backwards consuming its tape in the reverse ...
Akuri's user avatar
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Is it possible to make N-way Controlled-NOTs out of Toffoli gates, without extra work bits?

I'm working on exercise 4.29 of Nielsen and Chuang: Find a circuit containing O(n^2) Toffoli, CNOT, and single qubit gates which implements a $C^n(X)$ gate (for n >3), using no work qubits. As ...
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What difference does it make when universal classical gates in quantum computation are reversible but not unitary?

As I've come across Grovers algorithm I dont understand why when computing F(X), which is an oracle function people use classical reversible circuits(toffoli, fredkin) to evaluate the circuit. Why can'...
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What's flawed about the "save-the-input" method of reversible computing?

I'm an undergraduate just beginning to read about reversible computing. I know that, because of Landauer's principle, irreversible computations dissipate heat (and reversible ones do not). I brought ...
Eli Rose's user avatar
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A programming language that can only implement computable bijective functions?

Are there programming languages(or logic) that can implement(or express) a function $f:\mathbb{N}\to \mathbb{N}$ if and only if $f$ is a computable bijective functions?
Chao Xu's user avatar
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