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From: PG Bug reporting form <noreply@postgresql.org>
To: pgsql-bugs@lists.postgresql.org
Cc: malis@pgrust.com
Subject: BUG #19593: area(circle) silently returns Infinity instead of raising "value out of range: overflow"
Date: Sat, 01 Aug 2026 03:07:25 +0000
Message-ID: <19593-d80bd21f90d32234@postgresql.org> (raw)

The following bug has been logged on the website:

Bug reference:      19593
Logged by:          Michael Malis
Email address:      malis@pgrust.com
PostgreSQL version: 18.3
Operating system:   Debian (official Docker image), aarch64
Description:        

I'm not sure what you'll want to do with this one, but I figured I would at
least report it. The cause seems to be a bug in gcc.

area(circle) returns Infinity where it must raise ERROR 22003 "value out of
range: overflow".  The overflow check in float8_mul() is present in the
source
but is absent from the generated code, because gcc 13 and later delete it at
-O1 and above.

The same binary raises the error correctly for the equivalent SQL-level
expression, and for a circle whose radius overflows one step earlier, so
this
is not "PostgreSQL does not check circle areas".

    -- WRONG: no error, returns Infinity
    SELECT area(circle '<(0,0),1e154>');
                      area
    ------------------------
                   Infinity

    -- CORRECT (control): the *inner* multiply overflows, so the surviving
    -- check fires
    SELECT area(circle '<(0,0),1e200>');
    ERROR:  value out of range: overflow

    -- CORRECT (control): the same arithmetic, expressed in SQL
    SELECT 1e154::float8 * 1e154::float8 * pi();
    ERROR:  value out of range: overflow

    -- sane value, for reference
    SELECT area(circle '<(0,0),1e10>');
           area
    -------------------------
     3.1415926535897933e+20

1e154 * 1e154 = 1e308, which is finite (below DBL_MAX); multiplying that by
pi
overflows.  Behaviour is identical whether the expression is constant-folded
at
plan time or evaluated at runtime:

    SELECT area(c) FROM (VALUES (circle '<(0,0),1e154>')) t(c);   --
Infinity

NaN and Infinity radii behave correctly (NaN -> NaN, Infinity -> Infinity).


WHERE IT COMES FROM

src/backend/utils/adt/geo_ops.c:5159

    static float8
    circle_ar(CIRCLE *circle)
    {
        return float8_mul(float8_mul(circle->radius, circle->radius), M_PI);
    }

src/include/utils/float.h:207

    static inline float8
    float8_mul(const float8 val1, const float8 val2)
    {
        float8      result;

        result = val1 * val2;
        if (unlikely(isinf(result)) && !isinf(val1) && !isinf(val2))
            float_overflow_error();
        ...

Two float8_mul calls are inlined into one function.  gcc keeps the first
copy's
overflow check and deletes the second's.

Disassembly of the shipped binary (circle_area; symbols are present in
.dynsym).
gcc lowers isinf(x) to |x| > DBL_MAX, with d30 = 0x7fefffffffffffff:

    ; inner multiply -- check intact
    5540dc  fmul d31, d29, d29        ; r*r
    5540e0  fcmp d31, d30
    5540e4  b.le 5540fc
    5540e8  fabs d29, d29             ; |r|  <- the !isinf(val1) test
    5540ec  fcmp d29, d30
    5540f0  b.le 554154
    554154  bl   float_overflow_error ; raises

    ; outer multiply -- operand test gone
    554104  adrp x0, 76c000
    554108  ldr  d29, [x0, #568]      ; M_PI
    55410c  fmul d31, d31, d29        ; (r*r) * M_PI
    554110  fcmp d31, d30
    554114  b.le 554120
    554118  mov  x0, #0x7ff0000000000000   ; returns +Infinity
    55411c  b    55412c

Control reaches the outer multiply only via the b.le at 5540e4, i.e. only
when
r*r <= DBL_MAX, and M_PI is a finite constant.  So
"!isinf(val1) && !isinf(val2)" is true on that path and
float_overflow_error()
must be called.

Building from an unmodified 18.3 tree (git tag stamp 62d6c7d) with gcc 14.2
and
the same CFLAGS reproduces it, so this is not specific to Debian's
packaging:

    ./configure --without-readline --without-zlib --without-icu \
        CFLAGS="-g -O2 -fno-strict-aliasing -fwrapv
-fexcess-precision=standard"
    make -C src/backend submake-generated-headers
    make -C src/backend/utils/adt geo_ops.o
    objdump -d geo_ops.o

circle_area then contains 3 fmul but only 1 call to float_overflow_error.
From
pristine source the outer check is removed entirely: there is no DBL_MAX
comparison after the second fmul at all, only the underflow test.

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  Subject: Re: BUG #19593: area(circle) silently returns Infinity instead of raising "value out of range: overflow"
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