feat: safe exponentiation #4637
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
- Adds configuration option `exponentiation.threshold` - An expression `b^n` where `b` and `n` are literals is not reduced by `whnf`, `simp`, and `isDefEq` if `n > exponentiation.threshold`. Motivation: prevents system from becoming irresponsive. TODO: improve support in the kernel. It is using a hard-coded limit for now.
github-actions
bot
added
the
toolchain-available
leanprover-community-mathlib4-bot
added a commit
to leanprover-community/batteries
that referenced
this pull request
Jul 3, 2024
leanprover-community-mathlib4-bot
added a commit
to leanprover-community/mathlib4
that referenced
this pull request
Jul 3, 2024
leanprover-community-mathlib4-bot
added
the
builds-mathlib
|
Mathlib CI status (docs):
|
What do you think about using |
eric-wieser
reviewed
Aug 7, 2024
| @@ -622,7 +634,7 @@ optional<expr> type_checker::reduce_nat(expr const & e) { | |||
| if (f == *g_nat_add) return reduce_bin_nat_op(nat_add, e); | |||
| if (f == *g_nat_sub) return reduce_bin_nat_op(nat_sub, e); | |||
| if (f == *g_nat_mul) return reduce_bin_nat_op(nat_mul, e); | |||
| if (f == *g_nat_pow) return reduce_bin_nat_op(nat_pow, e); | |||
| if (f == *g_nat_pow) return reduce_pow(e); | |||
There was a problem hiding this comment.
I'm a little worried that this doesn't actually help; I think when I tried this patch, instead of:
- Lean asks GMP to compute a very large natural, using lots of CPU or perhaps running out of heap memory
The result is now:
- Lean refuses to expand
a ^ nvia nat reduction a ^ nis expanded toa * a ^ (n - 1), allocating small objects and filling up the stack- Lean refuses to expand
a ^ (n - 1)via nat reduction - ...
- Recursion uses lots of CPU, and hits a stack overflow
There was a problem hiding this comment.
Here's the smallest test I could construct:
import Lean
import Qq
open Qq
theorem foo : 2 ^ 100000000 = (2 ^ 10000) ^ 10000 := by
run_tac do
(← Lean.Elab.Tactic.getMainGoal).assign
q(Eq.refl ((2 ^ 10000) ^ 10000))Apologies for the Qq use
There was a problem hiding this comment.
I think this was fixed by #4934!
Parcly-Taxel
added a commit
to Parcly-Taxel/lean4
that referenced
this pull request
Aug 9, 2024
In the Carleson project a non-fatal PANIC occurring in the application of certain applications of `Nat.reducePow` was discovered (https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/PANIC.20at.20Lean.2EExpr.2EappArg!.20application.20expected/near/457037665). We fix this regression from leanprover#4637. Fixes leanprover#4947.
Parcly-Taxel
added a commit
to Parcly-Taxel/lean4
that referenced
this pull request
Aug 9, 2024
In the Carleson project a non-fatal PANIC occurring in the application of certain applications of `Nat.reducePow` was discovered (https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/PANIC.20at.20Lean.2EExpr.2EappArg!.20application.20expected/near/457037665). We fix this regression from leanprover#4637. Fixes leanprover#4947.
Parcly-Taxel
added a commit
to Parcly-Taxel/lean4
that referenced
this pull request
Aug 12, 2024
In the Carleson project a non-fatal PANIC occurring in the application of certain applications of `Nat.reducePow` was discovered (https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/PANIC.20at.20Lean.2EExpr.2EappArg!.20application.20expected/near/457037665). We fix this regression from leanprover#4637. Fixes leanprover#4947.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Summary:
exponentiation.thresholdb^nwherebandnare literals is not reduced bywhnf,simp, andisDefEqifn > exponentiation.threshold.Motivation: prevents system from becoming irresponsive and/or crashing without memory.
TODO: improve support in the kernel. It is using a hard-coded limit for now.