org.vishia.bridgeC

Class DivideJc

java.lang.Object

org.vishia.bridgeC.DivideJc

public class DivideJc
extends java.lang.Object

This class supports some special division algorithm for processors which have not a division hardware on chip. A normal division is a more complex and longer algorithm. In Java it is not a problem, because the JVM supports division in a so long as proper way. But if algorithm for embedded processors are written with Java and used or translated to C, this algorithm may be proper. Therefore they are used in Java too.

An instance of this class contains 2 integer results for the quotient and the remainder of division. The 2 integer values may be returned in register variable though it is a data struct in C.

This class contains some static methods which returns an instance of this class as its result.

Field Summary

Fields

Modifier and Type	Field and Description
int	q Quotient and remainder.
int	r Quotient and remainder.
static int	version Version, history and license.

Constructor Summary

Constructors

Constructor and Description
DivideJc(int q, int r)

Method Summary

Modifier and Type	Method and Description
static DivideJc	divLess2pow(int val, int bit1, int bit2) This algorithm can be used if a number should be divide by a divisor which is near but less a power of 2 value and the divisor is build in a special simple form.
static void	main(java.lang.String[] args) Only for test in debug mode.
java.lang.String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

version

public static final int version

Version, history and license.

• 2013-12-31 Hartmut created.

Copyright/Copyleft: For this source the LGPL Lesser General Public License, published by the Free Software Foundation is valid. It means:

1. You can use this source without any restriction for any desired purpose.
2. You can redistribute copies of this source to everybody.
3. Every user of this source, also the user of redistribute copies with or without payment, must accept this license for further using.
4. But the LPGL is not appropriate for a whole software product, if this source is only a part of them. It means, the user must publish this part of source, but don't need to publish the whole source of the own product.
5. You can study and modify (improve) this source for own using or for redistribution, but you have to license the modified sources likewise under this LGPL Lesser General Public License. You mustn't delete this Copyright/Copyleft inscription in this source file.

If you are intent to use this sources without publishing its usage, you can get a second license subscribing a special contract with the author.

See Also:

Constant Field Values

q

public int q

Quotient and remainder.

r

public int r

Quotient and remainder.

Constructor Detail

DivideJc

public DivideJc(int q,
                int r)

Method Detail

divLess2pow

public static DivideJc divLess2pow(int val,
                                   int bit1,
                                   int bit2)

This algorithm can be used if a number should be divide by a divisor which is near but less a power of 2 value and the divisor is build in a special simple form. For example 0x3c0 is near 0x400. The idea is:

• A division by a power of 2 is a simple shift operation.
• A division by a number, which is near another number is aproximately the division by the other number adjusted by the abbreviation:

  y = x / 1.9  ~=  x / 2.0 + (x/2.0) * (2.0-1.9)/2.0; 
     

  One can divide by 2.0 instead divide by 1.9, then adjust the result with the ratio of abbreviation.
• A backward multiplying checks the correctness and calculates the remainder.

The divisor is given by 2 bits which describes the power of 2 - assembly of the divisor:

• bit1 The bit which describes the nearest power of 2 of divisor. (1< bit2 The bit which describes the distance from the nearest power of 2. 1< For example:

   bit1      bit2     divisor
     10         2     0x03fc  = 0x0400 - 0x0004
     10         6     0x03c0  = 0x0400 - 0x0040
     10         8     0x0300  = 0x0400 - 0x0100
     12         2     0x0ffc  = 0x1000 - 0x0004
     12         6     0x0fc0  = 0x1000 - 0x0040
     12         8     0x0f00  = 0x1000 - 0x0100
     12        10     0x0c00  = 0x1000 - 0x0400
   

  This algorithm is used to calculate indices of arrays in a IntegerBlockArray which has a size less a power of 2 because it can be used with the BlockHeap concept in C language.

Parameters:

val - Any integer value, the dividend.

bit1 - The bit which describes the nearest power of 2 of divisor. (1<

bit2 - The bit which describes the distance from the nearest power of 2. 1<

Returns:

quotient and remainder.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

main

public static void main(java.lang.String[] args)

Only for test in debug mode.

Parameters:

args - not used.