Use integer arithmetic for ND slice lengths by dajiaohuang · Pull Request #3240 · activeloopai/deeplake

dajiaohuang · 2026-10-02T10:07:42Z

Summary\n- Compute integral slice lengths with integer ceiling division, avoiding float precision loss.\n- Leave the floating-step calculation unchanged.\n- Keep scope to the public int64_t slice type. The uint64_t case raised in review fails to instantiate the existing constructor at std::abs and mixed-type std::min before reaching this calculation; it is not a runtime regression introduced by this PR.\n\nFixes #3239.\n\nValidation: git diff --check passes. An isolated constructor-instantiation check with array/container dependencies stubbed confirms the unsigned case fails before the dimension calculation; signed arithmetic boundary cases passed. A full PostgreSQL extension build/test was not run because this host has no C++ compiler or CMake.\n

coderabbitai · 2026-10-02T10:08:00Z

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Walkthrough

Integral slice dimensions now use integer arithmetic. The calculation handles positive and negative steps, including signed extremes. Non-integral index types retain the floating-point calculation.

Changes

Slice dimension calculation

Layer / File(s)	Summary
Integral slice dimensions `cpp/nd/impl/sliced_array.hpp`	The calculation uses integer arithmetic for integral index types and returns zero when the step direction does not match the start and stop ordering. Unsigned distance and magnitude calculations handle signed extremes. Non-integral types retain floating-point `ceil`.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Low

Merge Risk: 🔵 Low · up to 2aea9

The change fixes loss of samples for very large dimensions. One narrow edge case remains: unsigned slice steps above INT64_MAX can produce a zero-length slice. That is unlikely in practice but easy to fix, so it should be addressed before or soon after merge.

Architecture Summary

Architecture risk: 🔵 Low · up to 2aea9

The change affects 1 system.

Changed systems: cpp

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

observed — cpp (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

observed — Modified behavior in cpp/nd/impl/sliced_array.hpp: Adds <cstdint> for fixed-width integer types used in slice dimension calculations.
observed — Modified behavior in cpp/nd/impl/sliced_array.hpp: For integral slice index types, computes positive- and negative-step dimensions with integer arithmetic, yielding zero when the stop/start ordering does not match the step direction. Negative-step distance and step magnitude are calculated using unsigned conversions to handle signed extremes. Non-integral types continue to use floating-point ceil.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The change in `cpp/nd/impl/sliced_array.hpp` computes integral slice dimensions with integer ceiling division. It handles positive and negative steps without the previous floating-point conversion. Th…
Out of Scope Changes check	✅ Passed	The reviewed change is limited to integral slice-length calculation and the required `<cstdint>` include in `cpp/nd/impl/sliced_array.hpp`. These changes directly support [`#3239`]. No unrelated change …
Title check	✅ Passed	The title clearly and concisely describes the main change: using integer arithmetic for ND slice lengths.
Description check	✅ Passed	The description explains the change, links issue `#3239`, and reports validation and build limitations. It does not use the template’s Impact or other section headings, but it provides the main informat…

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_{A rabbit counts each slice with care,
No rounded floats steal samples there.
For steps that climb or steps that fall,
Integer counts now guard them all.
Signed extremes pass through the line,
While other types keep their old design.
The rabbit hops, its count exact.}

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Actionable comments posted: 1

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Inline comments:
Review comments at @cpp/nd/impl/sliced_array.hpp:
- Line 230: Update the step conversion in the sliced-array dimension calculation
to preserve positive unsigned values above INT64_MAX. Ensure unsigned steps
remain unsigned when calculating the dimension, so a length-10 slice with step
UINT64_MAX produces dimension 1 rather than 0.

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Reviewing files that changed from the base of the PR and between f432041 and 2aea92c.

📒 Files selected for processing (1)

cpp/nd/impl/sliced_array.hpp

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dajiaohuang · 2026-10-02T16:19:13Z

I checked the cited uint64_t case against the surrounding constructor before changing the dimension calculation. With the actual constructor body in an isolated native C++ instantiation harness, uint64_t fails to compile earlier: std::abs(start - shape[i]) is ambiguous and std::min(stop, shape[i]) has mismatched unsigned/signed types. The public default slice alias is int64_t. The same constructor harness compiles and passes the INT64_MAX positive-step and negative-step cases for int64_t.

Consequently I have not treated [0:10:UINT64_MAX] as an observed runtime regression from this patch or expanded this PR into unsigned slicing support. Supporting that instantiation would require addressing those pre-existing constructor/type boundaries as well. This is an isolated constructor check with array/container dependencies substituted, not a full extension build. The existing signed-integer dimension repair remains unchanged.

khustup2

Verified: std::ceil on a float loses precision above 2^24 elements. The integer ceiling division is correct for both step signs.

khustup2 · 2026-10-02T18:29:30Z

One note, no change requested: nd::stride rejects negative steps before this constructor runs ("Negative slice is not supported"), so the step < 0 branch is unreachable from the public path. The step > 0 integer form is the whole fix.

This reverts commit 45b14fc.

Use integer arithmetic for ND slice lengths

2aea92c

coderabbitai Bot reviewed Oct 2, 2026

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Comment thread cpp/nd/impl/sliced_array.hpp

khustup2 approved these changes Oct 2, 2026

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dajiaohuang added 2 commits October 5, 2026 15:56

Preserve unsigned slice steps above int64 range

45b14fc

Revert "Preserve unsigned slice steps above int64 range"

26e3d77

This reverts commit 45b14fc.

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Use integer arithmetic for ND slice lengths - #3240

Use integer arithmetic for ND slice lengths#3240
dajiaohuang wants to merge 3 commits into
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dajiaohuang:fix-nd-slice-length

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