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JudyHS(3) Library Functions Manual JudyHS(3)


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.


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()


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


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

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");
if (*PValue == 0) // check if duplicate
printf("Duplicate lines %lu:%lu:%s", *PValue, LineNumb, Index);
*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); }


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


Judy(3), Judy1(3), JudyL(3), JudySL(3),
the Judy website,, for further information and Application Notes.