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4392. simd::unchecked_load misses difference type casting

Section: 29.10.8.7 [simd.loadstore] Status: New Submitter: Hewill Kang Opened: 2025-09-29 Last modified: 2025-10-22

Priority: 3

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Discussion:

Currently, simd::unchecked_load/partial_load/unchecked_store/partial_store construct a span via span(first, n) when taking an iterator first and its difference type n.

However, the construction is ill-formed when the difference type is an integer-class type; we should perform an explicit casting here.

[2025-10-22; Reflector poll.]

Set priority to 3 after reflector poll.

Question was raised if we should use size_t instead of iter_difference_t for consistency with span.

Proposed resolution:

This wording is relative to N5014.

1. In subclause 29.10.8.7 [simd.loadstore] replace all occurrences of

   R(first, n)
   

   by

   R(first, static_cast<size_t>(n))