HASHTAB

Prolog  

Control Block Contents  
   HASHTAB DSECT

Storage Layout  

Cross Reference (Contains links to field and bit definitions)  

HASHTAB Prolog

 Name       : HASHTAB
 Description: Hash Table Complex
 DSECT      : HASHTAB
 Function   : HASHTAB is used exclusively by file management
              to reduce the paging overhead when searching
              for a file on a read/write disk. It contains a
              header plus a pointer array with the address of
              each hyperblock associated with the disk, and a
              scatter index table with a 4-byte entry for
              each file on the disk. HASHTAB is called by the
              HASHTAB macro.

HASHTAB Control Block Content

HASHTAB DSECT

Hex   Dec Type/Val   Lng Label (dup)    Comments
---- ---- --------- ---- -------------- --------
0000    0 Structure      HASHTAB        Hash Table Complex
     H E A D E R
0000    0 Signed       4 HYPTSIZE       Size of Hyperblock Address Table
                                        (bytes)
0004    4 Signed       4 SCTSIZE        Size of Scatter Table (bytes)
0008    8 Signed       4 NSCTSLOT       Number of 4 byte slots in Scatter
                                        Table
000C   12 Signed       4 NSCTUSED       Number of used Scatter Table
                                        slots
0010   16 Character    7 HASHEYEC       Hash Table eyecatcher
0017   23 Character    1 HASHVERS       Hash Table version number
0018   24 Character    8 *              Reserved
          00000020       HSHLENHD       *-HASHTAB Size of header
     H Y P E R B L O C K A D D R E S S T A B L E
0020   32 Signed       4 HYPTABLE (0)   Start of Hyperblock Address
                                        Portion
0020   32 Signed       4 HYPADD         Address of hyperblock
          00000004       HADDLEN        *-HYPADD Size of an address entry
     S C A T T E R T A B L E
0024   36 Signed       4 SCATTRTB (0)   Start of Scatter Table Portion
0024   36 Signed       3 HTABINDX       Index into hyperblock address
                                        table
0027   39 Character    1 SECHBYTE       Secondary hash byte
          00000004       SLOTSIZE       *-HTABINDX Size of a Scatter
                                        Table slot

HASHTAB Storage Layout

          
*** HASHTAB - Hash Table Complex
*
*     +---------------------------+---------------------------+
*   0 |         HYPTSIZE          |         SCTSIZE           |
*     +---------------------------+---------------------------+
*   8 |         NSCTSLOT          |         NSCTUSED          |
*     +---------------------------+--------------------+------+
*  10 |                   HASHEYEC                     |:HVERS|
*     +------------------------------------------------+------+
*  18 |///////////////////////////////////////////////////////|
*     +---------------------------+--------------------+------+
*  20 |          HYPADD           |     HTABINDX       |:HBYTE|
*     +---------------------------+--------------------+------+
*  28
*
*** HASHTAB - Hash Table Complex

HASHTAB Cross Reference

Symbol         Dspl Value
-------------- ---- -----
HADDLEN        0020 00000004
HASHEYEC       0010
HASHVERS       0017
HSHLENHD       0018 00000020
HTABINDX       0024
HYPADD         0020
HYPTABLE       0020
HYPTSIZE       0000
NSCTSLOT       0008
NSCTUSED       000C
SCATTRTB       0024
SCTSIZE        0004
SECHBYTE       0027
SLOTSIZE       0027 00000004