Why does the SIMD path use < instead of <= in std.mem.findScalarPos?

A Zig developer questioned why the SIMD path in std.mem.findScalarPos uses `<` instead of `<=` when checking if a block fits within the slice, noting that a block ending exactly at slice.len is valid. The discussion references TigerBeetle's blog post on Index, Count, Offset, Size to explain the distinction, but the original poster maintains that the end position should allow `<=`.

noobie https://ziggit.dev/u/noobie 1 I’m trying to understand the reasoning behind the < checks in this SIMD code. The relevant part is: js if i + 2 block len < slice.len { const mask: Block = @splat value ; while true { inline for 0..2 | | { const block: Block = slice i.. 0..block len . ; const matches = block == mask; if @reduce .Or, matches { return i + std.simd.firstTrue matches .?; } i += block len; } if i + 2 block len = slice.len break; } } Then the tail handling has: js const block x len = block len / 1 << j ; if i + block x len < slice.len { const block: BlockX = slice i.. 0..block x len . ; ... } I’m wondering why these use < instead of <= . If a block ends exactly at slice.len , wouldn’t it still be valid? For example, if slice.len == 16 and block len == 8 , the block 8..16 fits completely. With < , that final block is left for the scalar loop instead. I’m mainly trying to understand if there is a performance, bounds-check, or other implementation reason for using < here that I’m missing. Looks to me like the usual difference between Offset i and Size slice.len . There is a nice visualization at TigerBeetles Blog post Index, Count, Offset, Size https://tigerbeetle.com/blog/2026-02-16-index-count-offset-size/ I think the use of < is appropriate here. noobie https://ziggit.dev/u/noobie 3 I see the index/count distinction, but in this case I think i + block len is an end position rather than an index. If i = 8 , block len = 8 , and slice.len = 16 , the accessed range is 8..16 , so the block fits exactly. That’s why I’m wondering why the condition uses < rather than <= .