Ubuntu Manpage: JudyHS - C library for creating and accessing a dynamic array, using an array-of-bytes of

Provided by: libjudy-dev_1.0.5-5.1build1_amd64

NAME

       JudyHS  - C library for creating and accessing a dynamic array, using an array-of-bytes of
       Length as an Index and a word as a Value.

SYNOPSIS

       cc [flags] sourcefiles -lJudy

       #include <Judy.h>

       Word_t  * PValue;                           // JudyHS array element
       int       Rc_int;                           // return flag
       Word_t    Rc_word;                          // full word return value
       Pvoid_t   PJHSArray = (Pvoid_t) NULL;       // initialize JudyHS array
       uint8_t * Index;                            // array-of-bytes pointer
       Word_t    Length;                           // number of bytes in Index

       JHSI( PValue,  PJHSArray, Index, Length);   // JudyHSIns()
       JHSD( Rc_int,  PJHSArray, Index, Length);   // JudyHSDel()
       JHSG( PValue,  PJHSArray, Index, Length);   // JudyHSGet()
       JHSFA(Rc_word, PJHSArray);                  // JudyHSFreeArray()

DESCRIPTION

A JudyHS array is the equivalent of an array of word-sized value/pointers. An Index is a
pointer to an array-of-bytes of specified length: Length. Rather than using a null
terminated string, this difference from JudySL(3) allows strings to contain all bits
(specifically the null character). This new addition (May 2004) to Judy arrays is a
hybird using the best capabilities of hashing and Judy methods. JudyHS does not have a
poor performance case where knowledge of the hash algorithm can be used to degrade the
performance.

Since JudyHS is based on a hash method, Indexes are not stored in any particular order.
Therefore the JudyHSFirst(), JudyHSNext(), JudyHSPrev() and JudyHSLast() neighbor search
functions are not practical. The Length of each array-of-bytes can be from 0 to the
limits of malloc() (about 2GB).

The hallmark of JudyHS is speed with scalability, but memory efficiency is excellent. The
speed is very competitive with the best hashing methods. The memory efficiency is similar
to a linked list of the same Indexes and Values. JudyHS is designed to scale from 0 to
billions of Indexes.

A JudyHS array is allocated with a NULL pointer

Pvoid_t PJHSArray = (Pvoid_t) NULL;

Because the macro forms of the API have a simpler error handling interface than the
equivalent functions, they are the preferred way to use JudyHS.

JHSI(PValue, PJHSArray, Index, Length) // JudyHSIns()

       Given  a  pointer  to a JudyHS array (PJHSArray), insert an Index string of length: Length
       and a Value into the JudyHS array:  PJHSArray.  If the Index is successfully inserted, the
       Value is initialized to 0.  If the Index was already present, the Value is not modified.

       Return  PValue  pointing to Value.  Your program should use this pointer to read or modify
       the Value, for example:

       Value = *PValue;
       *PValue = 1234;

       Note: JHSI() and JHSD can reorganize the JudyHS array.  Therefore, pointers returned  from
       previous JudyHS calls become invalid and must be re-acquired (using JHSG()).

JHSD(Rc_int, PJHSArray, Index, Length) // JudyHSDel()

       Given  a  pointer to a JudyHS array (PJHSArray), delete the specified Index along with the
       Value from the JudyHS array.

       Return Rc_int set to 1 if successfully removed from the array.  Return Rc_int set to 0  if
       Index was not present.

JHSG(PValue, PJHSArray, Index, Length) // JudyHSGet()

       Given a pointer to a JudyHS array (PJHSArray), find Value associated with Index.

       Return  PValue  pointing to Index's Value.  Return PValue set to NULL if the Index was not
       present.

JHSFA(Rc_word, PJHSArray) // JudyHSFreeArray()

       Given a pointer to a JudyHS array (PJHSArray), free the entire array.

       Return Rc_word set to the number of bytes freed and PJHSArray set to NULL.

ERRORS: See: Judy_3.htm#ERRORS

EXAMPLES

       Show how to program with the JudyHS macros.  This program will print duplicate  lines  and
       their line number from stdin.

       #include <unistd.h>
       #include <stdio.h>
       #include <string.h>
       #include <Judy.h>

       //  Compiled:
       //  cc -O PrintDupLines.c -lJudy -o PrintDupLines

       #define MAXLINE 1000000                 /* max fgets length of line */
       uint8_t   Index[MAXLINE];               // string to check

       int     // Usage:  PrintDupLines < file
       main()
       {
           Pvoid_t   PJArray = (PWord_t)NULL;  // Judy array.
           PWord_t   PValue;                   // Judy array element pointer.
           Word_t    Bytes;                    // size of JudyHS array.
           Word_t    LineNumb = 0;             // current line number
           Word_t    Dups = 0;                 // number of duplicate lines

           while (fgets(Index, MAXLINE, stdin) != (char *)NULL)
           {
               LineNumb++;                     // line number

               // store string into array
               JHSI(PValue, PJArray, Index, strlen(Index));
               if (PValue == PJERR)            // See ERRORS section
               {
                   fprintf(stderr, "Out of memory -- exit\n");
                   exit(1);
               }
               if (*PValue == 0)               // check if duplicate
               {
                   Dups++;
                   printf("Duplicate lines %lu:%lu:%s", *PValue, LineNumb, Index);
               }
               else
               {
                   *PValue = LineNumb;         // store Line number
               }
           }
           printf("%lu Duplicates, free JudyHS array of %lu Lines\n",
                           Dups, LineNumb - Dups);
           JHSFA(Bytes, PJArray);              // free JudyHS array
           printf("JudyHSFreeArray() free'ed %lu bytes of memory\n", Bytes);
           return (0);
       }

AUTHOR

       JudyHS was invented and implemented by Doug Baskins after retiring -Packard.