Judy1(3)

📦

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okay so bestie, this is Judy1(3) from the Library Functions Manual — yes, the Judy1 macros page — and it's literally the C-library moment for creating and accessing a dynamic array of bits, using any value of a word as an index. no cap, let's get into it. 💖

🌸 NAME 🌸

Judy1 macros — a C library for creating and accessing a dynamic array of bits, using any value of a word as an index. 🎀

✨ SYNOPSIS ✨

compile it like this, bestie:

cc [flags] sourcefiles -lJudy

#include <Judy.h>

int     Rc_int;                          // return code - integer
Word_t  Rc_word;                         // return code - unsigned word
Word_t  Index, Index1, Index2, Nth;

Pvoid_t PJ1Array = (Pvoid_t) NULL;       // initialize Judy1 array

J1S( Rc_int,  PJ1Array, Index);          // Judy1Set()
J1U( Rc_int,  PJ1Array, Index);          // Judy1Unset()
J1T( Rc_int,  PJ1Array, Index);          // Judy1Test()
J1C( Rc_word, PJ1Array, Index1, Index2); // Judy1Count()
J1BC(Rc_int,  PJ1Array, Nth, Index);     // Judy1ByCount()
J1FA(Rc_word, PJ1Array);                 // Judy1FreeArray()
J1MU(Rc_word, PJ1Array);                 // Judy1MemUsed()
J1F( Rc_int,  PJ1Array, Index);          // Judy1First()
J1N( Rc_int,  PJ1Array, Index);          // Judy1Next()
J1L( Rc_int,  PJ1Array, Index);          // Judy1Last()
J1P( Rc_int,  PJ1Array, Index);          // Judy1Prev()
J1FE(Rc_int,  PJ1Array, Index);          // Judy1FirstEmpty()
J1NE(Rc_int,  PJ1Array, Index);          // Judy1NextEmpty()
J1LE(Rc_int,  PJ1Array, Index);          // Judy1LastEmpty()
J1PE(Rc_int,  PJ1Array, Index);          // Judy1PrevEmpty()

that's the whole lineup, periodt. 💅

🦋 DESCRIPTION 🦋

A Judy1 array is the equivalent of a bit array or bit map. A bit is addressed by an Index (key). The array may be sparse, and the Index may be any word-sized Value. If an index is present, it represents a set bit (a bit set represents an index present). If an index is absent, it represents an unset bit (a bit unset represents an absent index). 🫶

A Judy1 array is allocated with a NULL pointer:

Pvoid_t PJ1Array = (Pvoid_t) NULL;

Memory to support the array is allocated as bits are set, and released as bits are unset. If the Judy1 pointer (PJ1Array) is NULL, all bits are unset (and the Judy1 array requires no memory). lowkey iconic. ✨

As with an ordinary array, a Judy1 array contains no duplicate indexes. 🎀

Using the macros described here, rather than the Judy1 function calls, the default error handling sends a message to the standard error and terminates the program with exit(1). For other error handling methods, see the ERRORS section. 💀

Because the macro forms are sometimes faster and have a simpler error handling interface than the equivalent functions, they are the preferred way of calling the Judy1 functions. slay. 🔥

J1S(Rc_int, PJ1Array, Index); — this is Judy1Set(). It sets Index's bit in the Judy1 array PJ1Array. Return Rc_int set to 1 if Index's bit was previously unset (successful), otherwise 0 if the bit was already set (unsuccessful). 💖
J1U(Rc_int, PJ1Array, Index); — this is Judy1Unset(). It unsets Index's bit in the Judy1 array PJ1Array; that is, remove Index from the Judy1 array. Return Rc_int set to 1 if Index's bit was previously set (successful), otherwise 0 if the bit was already unset (unsuccessful). 🦋
J1T(Rc_int, PJ1Array, Index); — this is Judy1Test(). It tests if Index's bit is set in the Judy1 array PJ1Array. Return Rc_int set to 1 if Index's bit is set (Index is present), 0 if it is unset (Index is absent). 👑
J1C(Rc_word, PJ1Array, Index1, Index2); — this is Judy1Count(). It counts the number of indexes present in the Judy1 array PJ1Array between Index1 and Index2 (inclusive). Return Rc_word set to the count. A return Value of 0 can be valid as a count, or it can indicate a special case for fully populated array (32-bit machines only). See Judy1Count() for ways to resolve this. To count all indexes present (population) in a Judy1 bit array, use:

J1C(Rc_word, PJ1Array, 0, -1);

Note: The -1 promotes to the maximum index, that is, all ones. 🧚

J1BC(Rc_int, PJ1Array, Nth, Index); — this is Judy1ByCount(). It locates the Nth index that is present in the Judy1 array PJ1Array (Nth = 1 returns the first index present). To refer to the last index in a fully populated array (all indexes present, which is rare), use Nth = 0. Return Rc_int set to 1 and Index set to the Nth index if found, otherwise return Rc_int set to 0 (the Value of Index contains no useful information). 💅
J1FA(Rc_word, PJ1Array); — this is Judy1FreeArray(). It frees the entire Judy1 array PJ1Array (much faster than using a J1N(), J1U() loop). Return Rc_word set to the number of bytes freed, and PJ1Array set to NULL. 🎀
J1MU(Rc_word, PJ1Array); — this is Judy1MemUsed(). Return Rc_word set to the number of bytes of memory currently in use by Judy1 array PJ1Array. This is a very fast routine, and may be used after a J1S() or J1U() call with little performance impact. 🌸

💫 Judy1 Search Functions 💫

The Judy1 search functions allow you to search for set or unset bits in the array. You may search inclusively or exclusively, in either forward or reverse directions. All of the search functions use a similar calling sequence. Rc_int is returned set to 1 for a successful search and the found Index is returned. Rc_int is returned set to 0 for an unsuccessful search, and Index contains no useful information. 😭

⚠️ fr fr: the return code Rc_int must be checked prior to using the returned Index, since a search failure is possible.

J1F(Rc_int, PJ1Array, Index); — this is Judy1First(). It searches (inclusive) for the first index present that is equal to or greater than the passed Index. (Start with Index = 0 to find the first index in the array.) J1F() is typically used to begin a sorted-order scan of the indexes present in a Judy1 array. 🌈
J1N(Rc_int, PJ1Array, Index); — this is Judy1Next(). It searches (exclusive) for the next index present that is greater than the passed Index. J1N() is typically used to continue a sorted-order scan of the indexes present in a Judy1 array, or to locate a "neighbor" of a given index. 🦋
J1L(Rc_int, PJ1Array, Index); — this is Judy1Last(). It searches (inclusive) for the last index present that is equal to or less than the passed Index. (Start with Index = -1, that is, all ones, to find the last index in the array.) J1L() is typically used to begin a reverse-sorted-order scan of the indexes present in a Judy1 array. ✨
J1P(Rc_int, PJ1Array, Index); — this is Judy1Prev(). It searches (exclusive) for the previous index present that is less than the passed Index. J1P() is typically used to continue a reverse-sorted-order scan of the indexes present in a Judy1 array, or to locate a "neighbor" of a given index. 💖
J1FE(Rc_int, PJ1Array, Index); — this is Judy1FirstEmpty(). It searches (inclusive) for the first absent index that is equal to or greater than the passed Index. (Start with Index = 0 to find the first index absent in the array.) 🌸
J1NE(Rc_int, PJ1Array, Index); — this is Judy1NextEmpty(). It searches (exclusive) for the next absent index that is greater than the passed Index. 🎀
J1LE(Rc_int, PJ1Array, Index); — this is Judy1LastEmpty(). It searches (inclusive) for the last absent index that is equal to or less than the passed Index. (Start with Index = -1 to find the last index absent in the array.) 🧚
J1PE(Rc_int, PJ1Array, Index); — this is Judy1PrevEmpty(). It searches (exclusive) for the previous absent index that is less than the passed Index. 💜

💀 ERRORS 💀

See: Judy_3.htm#ERRORS — that's the whole error section, bestie, it's linking you out. 🫶

🎀 EXAMPLE 🎀

In the following example, errors in the J1S() or J1U() calls go to a user-defined procedure, process_malloc_failure. This is not needed when you use the default JUDYERROR() macro, since the default causes your program to exit on all failures, including malloc() failure. 😭

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

int main()                       // Example program of Judy1 macro APIs
{
   Word_t Index;                 // index (or key)
   Word_t Rcount;                // count of indexes (or bits set)
   Word_t Rc_word;               // full word return value
   int    Rc_int;                // boolean values returned (0 or 1)

   Pvoid_t PJ1Array = (Pvoid_t) NULL; // initialize Judy1 array

   Index = 123456;
   J1S(Rc_int, J1Array, Index);  // set bit at 123456
   if (Rc_int == JERR) goto process_malloc_failure;
   if (Rc_int == 1) printf("OK - bit successfully set at %lu\n", Index);
   if (Rc_int == 0) printf("BUG - bit already set at %lu\n", Index);

   Index = 654321;
   J1T(Rc_int, J1Array, Index);  // test if bit set at 654321
   if (Rc_int == 1) printf("BUG - set bit at %lu\n", Index);
   if (Rc_int == 0) printf("OK - bit not set at %lu\n", Index);

   J1C(Rcount, J1Array, 0, -1);  // count all bits set in array
   printf("%lu bits set in Judy1 array\n", Rcount);

   Index = 0;
   J1F(Rc_int, J1Array, Index);  // find first bit set in array
   if (Rc_int == 1) printf("OK - first bit set is at %lu\n", Index);
   if (Rc_int == 0) printf("BUG - no bits set in array\n");

   J1MU(Rc_word, J1Array);       // how much memory was used?
   printf("%lu Indexes used %lu bytes of memory\n", Rcount, Rc_word);

   Index = 123456;
   J1U(Rc_int, J1Array, Index);  // unset bit at 123456
   if (Rc_int == JERR) goto process_malloc_failure;
   if (Rc_int == 1) printf("OK - bit successfully unset at %lu\n", Index);
   if (Rc_int == 0) printf("BUG - bit was not set at %lu\n", Index);

   return(0);
}

👑 AUTHOR 👑

Judy was invented by Doug Baskins and implemented by Hewlett-Packard. 👑

🌈 SEE ALSO 🌈

Judy(3), JudyL(3), JudySL(3), JudyHS(3), malloc(), the Judy website, http://judy.sourceforge.net, for more information and Application Notes. 🌈

xoxo, your Judy1 bestie 💅 — footer tea: the source/version tag here is just Judy1(3), and there's no date listed, so that's the whole sign-off vibe. 🎀

📦 where this page comes from

arch rolling: judy 1.0.5-10 · LGPL-2.0-or-later
nixpkgs unstable: judy 1.0.5
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-06: a language model's rewrite of the original, under its terms