Re^5: Why is the size even bigger after pack?

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Re^6: Why is the size even bigger after pack? by PerlOnTheWay (Monk) on Nov 04, 2011 at 01:30 UTC
You mentioned it's in previously allocated memory why??Isn't it created on the fly? Perl allocates more memory than required for string, that's what `xpv_cur/xpv_len` is there for	[reply] [d/l]
Re^7: Why is the size even bigger after pack? by ikegami (Patriarch) on Nov 04, 2011 at 03:01 UTC
No, the SV body isn't created at all for SVt_IV scalars. A SV usually has a head block and a body block (that's in addition to any string buffer, etc). SVt_IV scalars, rather exceptionally, don't have a body. Or rather they have a body, but it's location overlaps the head so that it never needs to be allocated. 5.12, 64 bit ints, 64 bit floats - - -+ <---+ : \| : +04 \| Usual SV head SVt_IV : \| --> +-----------------+ --> +-----------------+ +08 \| \| Pointer to body ------+ \| Pointer to body ------+ +04 \| \| \| +04 \| \| +0C \| \| \| \| \| +08 +-----------------+ \| +08 +-----------------+ +10 \| REFCNT \| \| \| REFCNT \| +0C +-----------+-----+ \| +0C +-----------+-----+ +14 \| FLAGS \| SVt \| \| \| FLAGS \| SVt \| +10 +-----------+-----+ \| +10 +-----------+-----+ +18 \| PV ---> +---------- \| \| IV/UV \| +14 \| \| ... \| +14 \| \| +1C \| +---------- \| \| \| +18 +-----------------+ \| +18 +-----------------+ +20 \| Usual SV body \| +-----------------+ <---+ \| NV \| \| \| +04 \| \| +-----------------+ +08 \| CUR \| \| \| +0C \| \| +-----------------+ +10 \| LEN \| \| \| +14 \| \| +-----------------+ +18 \| IV/UV \| \| \| +1C \| \| +-----------------+ +20 [download]	[reply] [d/l]
Re^8: Why is the size even bigger after pack? by PerlOnTheWay (Monk) on Nov 04, 2011 at 03:43 UTC
Can you represent it with an image instead?	[reply]
Re^9: Why is the size even bigger after pack? by ikegami (Patriarch) on Nov 04, 2011 at 07:27 UTC

You mentioned it's in previously allocated memory

why??Isn't it created on the fly?

Perl allocates more memory than required for string, that's what xpv_cur/xpv_len is there for

No, the SV body isn't created at all for SVt_IV scalars.

A SV usually has a head block and a body block (that's in addition to any string buffer, etc). SVt_IV scalars, rather exceptionally, don't have a body. Or rather they have a body, but it's location overlaps the head so that it never needs to be allocated.

5.12, 64 bit ints, 64 bit floats                    - - -+ <---+
                                                         :     |
                                                         : +04 |
     Usual SV head                      SVt_IV           :     |
--> +-----------------+            --> +-----------------+ +08 |
    | Pointer to body ------+          | Pointer to body ------+
+04 |                 |     |      +04 |                 | +0C
    |                 |     |          |                 |
+08 +-----------------+     |      +08 +-----------------+ +10
    | REFCNT          |     |          | REFCNT          |
+0C +-----------+-----+     |      +0C +-----------+-----+ +14
    | FLAGS     | SVt |     |          | FLAGS     | SVt |
+10 +-----------+-----+     |      +10 +-----------+-----+ +18
    | PV ---> +----------   |          | IV/UV           |
+14 |         |        ...  |      +14 |                 | +1C
    |         +----------   |          |                 |
+18 +-----------------+     |      +18 +-----------------+ +20
                            |
     Usual SV body          |
    +-----------------+ <---+
    | NV              |
    |                 | +04
    |                 |
    +-----------------+ +08
    | CUR             |
    |                 | +0C
    |                 |
    +-----------------+ +10
    | LEN             |
    |                 | +14
    |                 |
    +-----------------+ +18
    | IV/UV           |
    |                 | +1C
    |                 |
    +-----------------+ +20
[download]

[reply]
[d/l]

Can you represent it with an image instead?

[reply]