perf: replace unnecessary usize::try_from with as casts#1473
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Nicolas0315 wants to merge 1 commit intomemorysafety:mainfrom
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perf: replace unnecessary usize::try_from with as casts#1473Nicolas0315 wants to merge 1 commit intomemorysafety:mainfrom
usize::try_from with as casts#1473Nicolas0315 wants to merge 1 commit intomemorysafety:mainfrom
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Replace `usize::try_from(n).unwrap()` with `n as usize` in three locations: - `fn read_pal_indices` in decode.rs: block dimensions (w4, h4, bw4, bh4) are always non-negative per the AV1 spec. - Segmentation map update in decode.rs: the comment about needing checked casts for `from_raw_parts_mut` is stale — the code now uses bounds-checked `DisjointMut` indexing, so overflow in the cast would cause a bounds-check panic rather than UB. Remove the outdated comment. - `fn cfl_ac_rust` in ipred.rs: w_pad and h_pad are non-negative and immediately asserted to be less than width/height. This removes the overhead of the checked conversion (comparison + unwrap/panic path) on every call. Addresses memorysafety#1344.
kkysen
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Mar 2, 2026
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kkysen
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Could you leave inline comments saying that they're non-negative like you have in the PR description?
Also, we should probably update these variables/arguments/fields to be actually unsigned (e.g., u32), but not sure if we want to do that right here (feel free to do that if you'd like, though).
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Replace
usize::try_from(n).unwrap()withn as usizein three locations where the checked conversion is unnecessary:fn read_pal_indices(decode.rs:643): Block dimensions (w4, h4, bw4, bh4) are always non-negative per the AV1 spec.Segmentation map update (decode.rs:3062-3063): The original comment about needing checked casts for
from_raw_parts_mutis stale — the code now uses bounds-checkedDisjointMutindexing, so overflow in the cast would cause a bounds-check panic rather than UB. The outdated comment is removed.fn cfl_ac_rust(ipred.rs:1310): w_pad and h_pad are non-negative and immediately asserted to be less than width/height.This removes the overhead of the checked conversion (comparison + unwrap/panic path) on every call.
usize::try_froms withascasts #1344.