Class: ModuloNumber (private in Integer

• Inheritance
• Description
• Class protocol
  • instance creation
• Instance protocol
  • accessing
  • arithmetic
  • converting
• Examples

Inheritance:

   Object
   |
   +--Integer::ModuloNumber

Package:

stx:libbasic

Category:

Magnitude-Numbers

Owner:

Integer

Description:

This is a helper class to perform fast computation of the modulus.
(with big numbers, this does make a difference)

WARNING: this does only work with numbers which have no common
         divisor (which is true for cryptographic applications).
         So, use this only if you know what you are doing ...



[instance variables:]
    modulus       the modulus
    reciprocal    reciprocal of the modulus
    shift         shift count to cut off some bits

copyright
COPYRIGHT (c) 1999 by eXept Software AG
             All Rights Reserved

This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice.   This software may not
be provided or otherwise made available to, or used by, any
other person.  No title to or ownership of the software is
hereby transferred.

Class protocol:

 modulus: anInteger

Instance protocol:

 modulus

return the modulus

 modulus: n

set the modulus

 modulusOf: dividend

compute the aNumber modulo myself.
The shortcut works only, if dividend is < modulo * modulo
(When doing arithmethic modulo something).
Otherwise do it the long way

Usage example(s):

|m| m := self new modulus:7. m modulusOf:55.

Usage example(s):

fast (using moduloNumber with almost same-sized dividend and divisor): |m| m := self new modulus:123456789901398721398721931729371293712943794254034548369328469438562948623498659238469234659823469823658423659823658. Time millisecondsToRun:[ 100000 timesRepeat:[ m modulusOf:874928459437598375937451931729371293712943794254034548369328469438562948623498659238469234659823469823658423659823658. ] ]. 10730930127807326146398409623772237722337234475792709784029183368622308259008044569184592041059181058049458041058052

 asInteger

return the modulus

 asModuloNumber

Examples:

        17 asModuloNumber modulusOf:38

        38 \\ 17