1251366 - Consider cleaning up the bitfield in PrefTypeFlags in modules/libpref/prefapi.h

Status: RESOLVED DUPLICATE of bug 1418156

(Core :: Preferences: Backend, defect, P3)

Description

[Milan Sreckovic [:milan] (needinfo for best results)]

See bug 1249157 comment 3.  We have a uint16_t that stores both the preference type (int, string, bool), as well as some flags about that preference (has default, etc.)
Bit fiddling being what it is, we could consider using bool:1 or some such to clean the code.  It would be all internal to PrefTypeFlags at this point, the implementation is not exposed outside the class.

One thing to consider is the size of PrefHashEntry (also in prefapi.h).  Bug 1248521 reduced the size from 40 to 32 bytes, if any work is done in this bug, it shouldn't increase that value.

For example, the "obvious":
PrefType
bool flag:1
bool flag:1
...
bool flag:1

gets us back to 40 bytes.

Comment 1

[Milan Sreckovic [:milan] (needinfo for best results)]

Attachment: A bit verbose and inellegant, but keeps the size to 32 bytes.

Comment 2

[Milan Sreckovic [:milan] (needinfo for best results)]

Attachment: Clean source code, but hash table entry is back to 40 bytes.

Comment 3

[Milan Sreckovic [:milan] (needinfo for best results)]

It seems we care about the size, so we would not want option 2.  Arguably, option 1 is still nicer code than the existing version.

Comment 4

[Nicholas Nethercote [inactive]]

I ended up doing this in bug 1418156.