Re: Add bms_offset_members() function for bitshifting Bitmapsets

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>

To: Chao Li <li.evan.chao@gmail.com>

Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>

Date: 2026-04-14T23:45:12Z

Lists: pgsql-hackers

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v2-0001-Introduce-bms_offset_members-function.patch (application/octet-stream) patch v2-0001

Thanks for looking.

On Tue, 14 Apr 2026 at 20:46, Chao Li <li.evan.chao@gmail.com> wrote:
> +               if (((uint64) new_nwords - 1) * BITS_PER_BITMAPWORD + high_bit + offset_bits > PG_INT32_MAX)
> +                       elog(ERROR, "bitmapset overflow");

> This overflow check seems wrong. Because when high_bit + offset_bits > BITS_PER_BITMAPWORD, new_nwords has been increased by 1, so there high_bit + offset_bits are double counted.

Your idea of checking the old highest member plus the offset seems a
more robust method, so I've adjusted the patch to use that.

David