Re: [GENERAL] Linking in sin() as a C function

Karel Zak - Zakkr wrote:
>
> On Mon, 31 Jan 2000 mathprof(at)bigfoot(dot)com wrote:
>
> > I tried the following, one at a time, to create sin() for PostgreSQL:
> >
> > CREATE FUNCTION sin(float8) RETURNS float8 AS '/usr/lib/libm.so' LANGUAGE 'c';
> > CREATE FUNCTION sin(float4) RETURNS float4 AS '/usr/lib/libm.so' LANGUAGE 'c';
> > CREATE FUNCTION sin(float4) RETURNS float8 AS '/usr/lib/libm.so' LANGUAGE 'c';
> > CREATE FUNCTION sin(float8) RETURNS float4 AS '/usr/lib/libm.so' LANGUAGE 'c';
> >
> > Each of these gave different and odd results (and a 'segmentation fault'
> > at one point), but none of them gave the right answer. What am I doing
> > wrong?
>
> Yes, it is probably wrong. Very offen PG's buildin functions allocate memory
> for result and IMHO your trial wrong mixing pointers. See a backend/utils/atd
> in PG source as example.

More specifically, only 1,2 and 4 byte integer values may be passed by
call-by-value to userdefined C functions in PostgreSQL. That is, floats
are passed by reference (pointers) while the math lib passes them by
value - you have to write your own wrappers around the mathlib sin
function.

Sevo