I wrote:
> The POSIX standard says this about the exp(3) function:
> If x is -Inf, +0 shall be returned.
> At least on my Linux box, our version does no such thing:
> regression=# select exp('-inf'::float8);
> ERROR: value out of range: underflow
Now that I look, power() has similar issues:
regression=# select power('1.1'::float8, '-inf');
ERROR: value out of range: underflow
regression=# select power('0.1'::float8, 'inf');
ERROR: value out of range: underflow
regression=# select power('-inf'::float8, '-3');
ERROR: value out of range: underflow
regression=# select power('-inf'::float8, '-4');
ERROR: value out of range: underflow
contradicting POSIX which says
For |x| > 1, if y is -Inf, +0 shall be returned.
For |x| < 1, if y is +Inf, +0 shall be returned.
For y an odd integer < 0, if x is -Inf, -0 shall be returned.
For y < 0 and not an odd integer, if x is -Inf, +0 shall be returned.
I've had the same issue with multiplying two tiny numbers. Select 2e-300::float * 2e-300::float gives an underflow, and it is not a wanted thing. This looks like handmade implementation of IEEE754's underflow exception that should be an optional return flag in addition to well defined number, but became a stop-the-world exception instead. Had to build custom Postgres with that logic ripped off in the past to be able to multiply numbers. Will be happy if that "underflow" (and overflow) thing is removed.
If in doubt whether this exception should be removed, to follow the spec fully in this way you have to also raise exception on any inexact result of operations on floats.