Re: right() returns the whole string for the most negative n

Ewan Young <kdbase(dot)hack(at)gmail(dot)com> writes:

> diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
> index a09a9e5d5bb..3117069cf1a 100644
> --- a/src/backend/utils/adt/varlena.c
> +++ b/src/backend/utils/adt/varlena.c
> @@ -4714,7 +4714,17 @@ text_right(PG_FUNCTION_ARGS)
> int off;
>
> if (n < 0)
> - n = -n;
> + {
> + /*
> + * Negating PG_INT32_MIN would overflow, so clamp instead. Any n whose
> + * absolute value is at least the string's length skips the whole
> + * string, and len can't exceed PG_INT32_MAX, so this is equivalent.
> + */
> + if (unlikely(n == PG_INT32_MIN))
> + n = PG_INT32_MAX;
> + else
> + n = -n;
> + }

Instead of open-coding this, how about about using pg_neg_s32_overflow?

if (pg_neg_s32_overflow(n, &n))
n = PG_INT32_MAX;

This made me think we might want saturating versions of the
pg_*_overflow functions, but some quick grepping doesn't reveal any
other places using pg_*_overflow do it manually, so that feels like
premature generalisation.

- ilmari