Hash index table hash generator apparatus

Apparatus for generating a hash index table entry address from a virtual address in a data processing system, the data processing system having a main store, the virtual address having a first group of bits for addressing within an object and a second group of bits for addressing a particular object, where the hash index table size is variable and is based upon the size of the main store, the main store having a plurality of objects, comprising:

• a virtual address register containing a virtual address for addressing the main store;
• indicating means for indicating the number of entries in said hash index table;
• alignment means for aligning the first group of bits relative to the second group of bits based upon the number of entries in said hash index table as indicated by said indicating means;
• EXCLUSIVE-OR means for EXCLUSIVE-OR'ing the first group of bits with the second group of bits after the first and second group of bits have been aligned by said alignment means to produce a result having a number of bits encodable to represent the maximum number of entries in said hash index table;
• and
• bit eliminating means for eliminating bits from the result produced by said EXCLUSIVE-OR means based upon the number of entries in said hash index table indicated by said indicating means.

Apparatus for generating a hash index table entry address from a virtual address in a data processing system, the data processing system having a main store, the virtual address having first and second groups of bits for addressing a particular segment of virtual storage and a third group of bits for addressing within a segment of virtual storage, where the size of the hash index table is variable and is based upon the size of the main store, the main store having a plurality of segments, comprising:

• a virtual address register for storing a virtual address;
• indicating means for indicating the size of the hash index table;
• reversing means for reversing the order of the third group of bits;
• alignment means for aligning the first and second groups of bits relative to the group of bits produced by said reversing means based upon the size of the hash index table as indicated by said indicating means;
• EXCLUSIVE-OR means connected to receive the first and second groups of bits and the group of bits produced by said alignment means and operable to generate a result having a number of bits encodable to represent the maximum number of entries in the table;
• shift left means for shifting to the left one position the result produced by said EXCLUSIVE-OR means;
• bit eliminating means for eliminating high order bits from the result produced by said EXCLUSIVE-OR means and said shift left means based upon the size of the hash index table indicated by said indicating means;
• and
• adder means for adding the main store address of the beginning of the hash index table to the result obtained from said bit eliminating means, whereby the hash index table entry address corresponding to the virtual address stored in said virtual address register is obtained.