Add boundary checks in gen_associated_data_from_range()

[Copilot]

gen_associated_data_from_range() performed unchecked u32 arithmetic on user-supplied CLI values: end - start underflows when end < start, and end - start + 1 overflows when end == u32::MAX && start == 0.

Changes

• Input validation: Return CMDToolError early when end < start
• Checked arithmetic: Replace end - start + 1 with (end - start).checked_add(1), returning an error on overflow
• Tests: Add test_gen_associated_data_from_range_end_less_than_start and test_gen_associated_data_from_range_max_overflow

// Before (panics/wraps on bad input)
let num_ints = end - start + 1;

// After
if end < start {
    return Err(CMDToolError {
        details: format!("invalid range: end ({end}) must be greater than or equal to start ({start})"),
    });
}
let num_ints = (end - start).checked_add(1).ok_or_else(|| CMDToolError {
    details: format!("range [{start}, {end}] is too large: count overflows u32"),
})?;

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add boundary checks in gen_associated_data_from_range()</issue_title>
<issue_description>> Since start/end are user-provided (via the CLI wrapper), this function should defensively validate end >= start and avoid unchecked u32 arithmetic (currently end - start + 1 will overflow/panic when end < start, and can also overflow when end == u32::MAX && start == 0). Consider returning an error on invalid ranges and computing the count with checked arithmetic.

Originally posted by Copilot in #763</issue_description>

Comments on the Issue (you are Copilot in this section)

• Fixes Add boundary checks in gen_associated_data_from_range() #788

---

📱 Kick off Copilot coding agent tasks wherever you are with GitHub Mobile, available on iOS and Android.

[Copilot]

Pull request overview

This PR hardens diskann-tools’s gen_associated_data_from_range() against invalid user-supplied CLI ranges by validating end >= start and using checked arithmetic to prevent u32 underflow/overflow when computing the count written into the DiskANN binary header.

Changes:

• Added early input validation returning CMDToolError when end < start.
• Replaced end - start + 1 with checked arithmetic to detect the start=0, end=u32::MAX overflow case.
• Added unit tests covering end < start and maximum-range overflow.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Aditya Krishnan (arkrishn94)]

Looks fine Alex, happy to stamp after we resolve the two small comments.

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

❌ Patch coverage is 93.75000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.51%. Comparing base (72fc467) to head (a654a40).
⚠️ Report is 65 commits behind head on main.

Files with missing lines	Patch %	Lines
...-tools/src/utils/gen_associated_data_from_range.rs	93.75%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #847      +/-   ##
==========================================
+ Coverage   89.10%   89.51%   +0.41%     
==========================================
  Files         443      460      +17     
  Lines       83361    85454    +2093     
==========================================
+ Hits        74277    76497    +2220     
+ Misses       9084     8957     -127     

Flag	Coverage Δ
miri	89.51% <93.75%> (+0.41%)	⬆️
unittests	89.36% <93.75%> (+0.41%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...-tools/src/utils/gen_associated_data_from_range.rs	97.56% <93.75%> (-2.44%)	⬇️

... and 198 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.