FunctionPackage: exclToCDocOverviewCGDocRelNotesFAQIndexPermutedIndex
Allegro CL version 10.1
Unrevised from 10.0 to 10.1.
10.0 version

hash-primify

Arguments: int

Returns a positive fixnum suitable for a hash-table size greater than or equal to int, which should be a fixnum. With all fixnums below the limit, the value returned will be a prime number. The value is returned from a table, so the calculation is fast. For fixnums above the limit, the value returned is at least not divisible by 2, 3, 5, or 7. Results lose accuracy as they approach most-positive-fixnum.

Limits:

Limits are approximate, and may change in the future. Currently:

Granularity:

Not all prime numbers are returned. The prime number table is populated with an approximately 2% increment, so the difference between one result and the next possible result (for values of int under the limit) are approximately 2% apart:

cl-user(1): (excl:hash-primify 100000000)
100121387
cl-user(2): (excl:hash-primify (1+ *))
102123817
cl-user(3): (float (/ * **))
1.02
cl-user(4): 

There may be other prime numbers not returned by this function; but because it is the goal of this function to quickly return a size suitable for efficient hash-table operation, populating all primes is not necessary.


Copyright (c) 1998-2017, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 10.0 page.
Created 2017.2.15.

ToCDocOverviewCGDocRelNotesFAQIndexPermutedIndex
Allegro CL version 10.1
Unrevised from 10.0 to 10.1.
10.0 version