Horton

Re: pgsql: Provide overflow safe integer math inline functions.

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: pgsql-committers@postgresql.org, Michael Paquier <michael.paquier@gmail.com>
Date: 2017-12-13T21:37:54Z
Lists: pgsql-hackers 
Hi Michael,

On 2017-12-13 01:01:19 +0000, Andres Freund wrote:
> Provide overflow safe integer math inline functions.

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=dangomushi&dt=2017-12-13%2018%3A00%3A18

which seems half like a compiler bug to me. But either way, we gotta
work around it.  I suspect the reason configure test doesn't
sufficiently detect this here is because it's testing the function with
constant arguments.

Could you perhaps test whether replacing PGAC_C_BUILTIN_OP_OVERFLOW's body with something like
result
PG_INT64_TYPE a;
PG_INT64_TYPE b;
PG_INT64_TYPE result;
__builtin_mul_overflow(*(volatile PG_INT64_TYPE*) &a, *(volatile PG_INT64_TYPE*) &b, &result);

makes it fail? I'd rather not test this via the buildfarm, given that
dangomushi isn't the most frequently running / fastest animal.

- Andres

Commits

  1. Try harder to detect unavailability of __builtin_mul_overflow(int64).

  2. Try to detect runtime unavailability of __builtin_mul_overflow(int64).

  3. Fix a number of copy & paste comment errors in common/int.h.

  4. Provide overflow safe integer math inline functions.