meta-info read fails for large transformation values while write works

[sebastian-goeldi]

Hi Matthias,

I have found a somewhat nasty bug. There seems to be a slight asymmetry in writer vs reader for trans objects. Below is an (AI slopped) minimal working example (I am not convinced the description is correct, but I assume you can easily find the actual bug based on it, so I left it in).

"""
KLayout meta-info INT32_MIN round-trip bug — confirmed on 0.30.8 / 0.30.9.
Reproduces the failure integer overflow (written by gdsfactory/kfactory):
    RuntimeError: Range overflow on integer in Layout.read

Root cause: an integer `Trans` stored in meta-info serializes its coordinates as
BARE integers, e.g.  'p'=>[trans:r0 -2147483648,-2147483648]. KLayout's variant
reader parses such a bare integer as a signed 32-bit int. -2147483648 (= INT32_MIN)
is a VALID int32, but the parser reads the magnitude 2147483648 (> INT32_MAX
2147483647) before applying the sign, so it overflows. KLayout's own writer emits
the value, but its reader cannot read it back -> genuine "write ok / read fails".
"""

import klayout.db as db

print("klayout", db.__version__)


def roundtrip(x):
    ly = db.Layout()
    ly.create_cell("TOP")
    mi = db.LayoutMetaInfo("p", db.Trans(0, False, x, x))  # integer Trans, coord = x
    mi.persisted = True
    ly.add_meta_info(mi)
    ly.write("/tmp/tr.gds")  # WRITE always succeeds
    seg = open("/tmp/tr.gds", "rb").read()
    i = seg.find(b"META")
    try:
        db.Layout().read("/tmp/tr.gds")  # READ may fail
        print(f"  x={x:>12}  file={seg[i : i + 24]!r}...  READ OK")
    except BaseException as e:
        print(f"  x={x:>12}  file={seg[i : i + 24]!r}...  *** {type(e).__name__}: {e}")


print("[int Trans coordinate round-trip through GDS meta-info]")
roundtrip(-2147483647)  # INT32_MIN + 1  -> OK
roundtrip(-2147483648)  # INT32_MIN      -> fails on read

[klayoutmatthias]

What a border case :)

Thanks for reporting this problem.

Are you employing that kind of transformation to encode a missing optional one? In that case, maybe you like to use "nil" to represent non-existing transformations.

Best regards,

Matthias

[sebastian-goeldi]

Hi Matthias,

No, it was a conversion issue, i.e. DBU values written to a um value field which then causes 2m instead of 2mm offset ;)

dcplx_trans=DCplxTrans(1, 0, False, trans.disp.x, trans.disp.y) essentially ;)

Claude claimed it's getting coerced to INT_MIN in the transformation. Is it possible to throw errors (or warnings) on these cases already? I.e. when the transformation values exceeds them. Pretty sure it's like a python float/int (pretty sure those are long long or the float equivalent) which then gets mapped to the 32bit coordinate.

Essentially this problem:

>>> import klayout.db as db
>>> db.Trans(0, False, 111111111111111111, 0)
r0 -2074054201,0