Submitted by: @paulvink

Assigned to: @samofatov

SFID: 775003#⁠
Submitted By: paulvink

log( x, y ) should return the x-based log of y, according
to the description in ib_udf.sql. But in fact it calculates
and returns ln x / ln y. This is the y-based log of x, and
the _inverse_ of what it should return.

Observed under Windows SS 1.0.0, 1.0.3 and 1.6 Alpha,
but clearly universal if you look at the source in ib_udf.c

A patch - which simply swaps numerator and
denominator in the one-line function body - has been
posted yesterday to firebird-devel.

Leaving the code intact and changing the description is
also an option, but I would strongly advise against that
because:

a) in English and lots of other languages you name the
log base before the number. So it feels natural that a
function returning the base-a log of b should be called
as log( a, b ) -- just as div( a, b ) divides a by b, not b
by a.

b) We also have the UDF log10. If you call log10( 100 ),
the base is before the number. Again, the most natural
thing would be if log10( 100 ) == log( 10, 100 ).

Grtz,
Paul Vinkenoog