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However, the fixed length hash makes it manageable and easily … But index 1 already occupied, check index 2 it also occupied (data given), 3 also occupied. 3. I'm in doubt. Check passwordswithout storing their clear forms 3. Below is the implementation of hashing or hash table in C. Below is the implementation of hashing or hash table in C++. Cryptographic functions are used today by a wide range of applications. It is same as linear probing. A hash function is good if their mapping from the keys to the values produces few collisions and the hash values are uniformly distributed among the buckets. We need to specify the rule so that the compiler knows what to do. And it is the national standard of South Korea (KS X 3262). In this, we can see that 23 and 12 can be placed easily but 32 cannot as again 12 and 32 shares the same entry with the same index in the table, as per this method hash (key) = (32 + 1*1) % 10 = 3. Comment document.getElementById("comment").setAttribute( "id", "a633f171c39a732f35bff0010022489f" );document.getElementById("c37581b005").setAttribute( "id", "comment" ); Subscribe to our mailing list and get interesting stuff and updates to your email inbox. HMAC is a keyed hash function and was published in 1996 by Mihir Bellare, Ran Canetti and Hugo Krawczyk and adopted as a FIPS (Federal Information Processing Standards) standard in 2002. Autrement dit : à 1 fichier (ou à 1 mot) va correspondre une signature unique (le résultat de la fonction de hachage, soit le hash). But these hashing function may lead to collision that is two or more keys are mapped to same value. Second has to satisfy two rules; it must not be equal to 0 and entries must be probed. Does not throw exceptions when called. 1. Back to top: Advanced Search. THE CERTIFICATION NAMES ARE THE TRADEMARKS OF THEIR RESPECTIVE OWNERS. Let hash function is h, hash table contains  0 to n-1 slots. 11 mod 5 = 1. But due to this method even we have 10 elements of each range 1 lack, we should create table of size 1 lack for only 10 elements. This technique is very faster than any other data structure in terms of time coefficient. For example, md5 will produce 128-bit hashes and sha256 … If we substitute ASCII codes for these characters, then we get 90 - 48, this is equal to 42 which is ASCII code for '*' character. The core idea behind hash tables is to use a hash function that maps a large keyspace to a smaller domain of array indices, and then use constant-time array operations to store and retrieve the data.. 1. Recent Articles on Hashing… Probing hash function is: h (k, i) here k is the key value which is to be inserted. 6 Ways to Perfect the UI of Your Mobile App, Top 7 Mistakes AngularJS Developers Should Avoid, TCP/IP Socket Programming in C and C++ (Client Server Program), Elements can be stored at outside of the table, In open addressing elements should be stored inside the table only, In chaining at any time the number of elements in the hash table may greater than the size of the hash table. Most of the cases it will take O (n) time. If collision happened that element try to occupy at quadratic distance instead of linear distance. Page 1 of 1: JLA FORUMS | Computers & Technology | GENERAL TECHNICAL SUPPORT | Programming Language - C. All times are GMT - 5 Hours: Similar Topics; Moen T2401 Genta 2-Function or 3-Function Diverter Transfer Valve Trim (Citrus Heights) \$45 . In this again the element 32 can be placed using hash2 (key) = 5 – (32 % 5) = 3. A hash table is a randomized data structure that supports the INSERT, DELETE, and FIND operations in expected O(1) time. Example: If we are inserting 2, we find its hash value using h (2, 0) because it’s first collision. Judy . The functional call returns a hash value of its argument: A hash value is a value that depends solely on its argument, returning always the same value for the same argument (for a given execution of a program). It can be used for implementing data structures (hash tables) and checksums. Now delete(22) applied. If we substitute ASCII codes for these characters, then we get 90 - 48, this is equal to 42 which is ASCII code for '*' character. In hash table, the data is stored in an array format where each data value has its own unique index value. He spend most of his time in programming, blogging and helping other programming geeks. The enabled specializations of the hash template defines a function object that implements a hash function. But problem is if elements (for example) 2, 12, 22, 32, elements need to be inserted then they try to insert at index 2 only. This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in the cookie policy. HP … So it’s called linear probing. The used unkeyed hash function $$\mathcal{H}$$ in HMAC is often SHA-1, which implies that the used key $$K$$ is 512-bit. Open-sourcing F14 for faster, more memory-efficient hash tables. Dictionary data types. Some of the methods used for hashing are: Hash Table is a data structure which stores data in an associative manner. It is assumed that a good hash functions will map the message m within the given range in a uniform manner. So don't stop here your required element may present at next index. MohamedTaha98 / djb2 hash function.c. Hash function with n bit output is referred to as an n-bit hash function. LSH is a cryptographic hash function designed in 2014 by South Korea to provide integrity in general-purpose software environments such as PCs and smart devices. open addressing methods in this code when I used hash function that (pos+1)%hFn in that place just replace with another function. 1. Write a C Program to implement hashing. Created Oct 5, 2017. Thus this is known as a clustering problem, which can be solved by the following method. Then use HASH_ADD_INT, HASH_FIND_INT and macros to store, retrieve or delete items from the hash table. // If table is full we should break, if not check this, loop will go to infinite loop. Verify the integrityof a message or a file 2. In particular, they define an operator () const that: Accepts a single parameter of type Key. If it results “x” and the index “x” already contain a value then we again apply hash function that h (k, 1) this equals to (h (k) + 1) mod n. General form: h1 (k, j) = (h (k) + j) mod n. Example: Let hash table of size 5 which has function is mod 5 has already filled at positions 0, 2, 3. To avoid this kind of problems there are some techniques of hash functions that can be used. // INT_MIN and INT_MAX indicates that cell is empty. 1.2. 2. Share Remove Report: Ron Irvine. When using a hash function as part of a hash-table, one will want to quantize or in other words reduce the hash value to be within the range of the number of buckets in the hash-table. Your email address will not be published. Last Modified: 2010-04-15. C; 5 Comments. Hash function in c. 01618041 asked on 2004-12-13. Register | Login. A good hash function has the following characteristics. And i is number of collision with that element. Advantages by this method are there is no chance of primary clustering. Hashing is an important Data Structure which is designed to use a special function called the Hash function which is used to map a given value with a particular key for faster access of elements. 10 mod 5 = 0. In case of deletion chaining is the best method, If deletion is not required. This is a guide to the Hashing function in C. Here we discussed brief overview, with types of Hash function in C and collision resolution techniques in detail. printf(“Element not found in hash table\n”); how to add string values in your program? Recommended Articles. You’d initially use the hash function to determine where in the hash table to store a given key. In this diagram 12 and 32 can be placed in the same entry with index 2 but by this method, they are placed linearly. 1.4. Searching is dominant operation on any data structure. It crunches 64 bits at a time to produce a 64 bit result. Douglas Crockford 2017-02-02 Fash64 is an efficient hashing function. While it is possible to add a key to an unkeyed hash function (HMAC is a popular technique), SipHash is much more efficient. A typical crypto g raphic function takes for input a message of arbitrary size and produces a hash of fixed size. In this method the hash function with hash key is calculated as hash (key) = (hash (key) + x * x) % size of the table (where x =0, 1, 2 …). Hash function. In these types of hashing suppose we have numbers from 1- 100 and size of hash table =10. To solve this collision problem we use different types of hash function techniques. It is always crucial for an ETL process to have a change tracking mechanism to identify when a change has happened to any set of data and only process data that has changed. Meaning that, it takes an input text — no matter how long or small it is — but the output of the hash function will always be in a fixed length. The efficiency of mapping depends of the efficiency of the hash function used. Hash Table is a data structure which stores data in an associative manner. In hashing there is a hash function that maps keys to some values. Testing with 5,000,000 items. With them you can: 1. As the name says whenever a collision occurs then two elements should be placed on the same entry in the table, but by this method, we can search for next empty space or entry in the table and place the second element. In hashing there is a hash function that maps keys to some values. Example: elements to be placed in a hash table are 42,78,89,64 and let’s take table size as 10. Earlier when this concept introduced programmers used to create “Direct address table”. Fash64: The Fast Hash Function. Embed. Comment below if have queries or found anything incorrect in above tutorial for Hashing in C and C++. Embed Embed this gist in your website. But these hashing function may lead to collision that is two or more keys are mapped to same value. Here the next prob position will depend on two functions h1 and h2 also. Instead of that, the access time in the bucket is linear. Created Oct 8, 2019. En terme très concret, on peut voir une fonction de hachage (non cryptographique) comme un moyen de replier l'espace de données que l'on suppose potentiellement très grand et très peu rempli pour le faire entrer dans la mémoire de l'ordinateur. In C++, a hash table uses the hash function to compute the index in an array at which the value needs to be stored or searched. Next apply delete(32). e.g. Keep in mind that hash tables can be used to store data of all types, but for now, let’s consider a very simple hash function for strings. The typical features of hash functions are − 1. abc & cab both should have same keys. Unary function object class that defines the default hash function used by the standard library. 350* 350 = 122500, index = 25 as the middle part of the result (122500) is 25. CreateProof of work (used in crypto-currencies like Bitcoin or Ethereum) 4. In hash table, the data is stored in an array format where each data value has its own unique index value. This process is often referred to as hashing the data. Hash function: It is basically a mathematical operation that defines how we transform the input. Embed. Hash Function is a cryptographic function that takes a variable length of input and produces a fixed length output. These also called collision resolution techniques. I'm in doubt. Well, suppose at some moment c == 'Z', so this expression amounts to 'Z' - '0'. Implementation in C Most of the cases for inserting, deleting, updating all operations required searching first. Read more about C Programming Language. A Hash Table in C/C++ (Associative array) is a data structure that maps keys to values. This uses a hash function to compute indexes for a key. Now new element 10 will try to insert. But this time we do some minor modifications to that input. That array is called Hash Table. Output: Now for an integer the hash function returns the same value as the number that is given as input.The hash function returns an integer, and the input is an integer, so just returning the input value results in the most unique hash possible for the hash type. In hash table instead of putting one element in index we maintain a linked list. But index 0 already occupied. In some cases, the key is the datum itself. But it's present at index 3. In this case we call this as Collision. Hash functions are not reversible. If we take any data structure the best time complexity for searching is O (log n) in AVL tree and sorted array only. Skip to content. Developed by Troy D. Hanson, any C structure can be stored in a hash table using uthash. This article has a brief note on hashing (hash table and hash function). We have numbers from 1 to 100 and hash table of size 10. it's deleted. we respect your privacy and take protecting it seriously, This is code for linear probing in open addressing. The hash function 1. is available for the fundamental data types like booleans, inte… Chain hashing avoids collision. In general, the hash is much smaller than the input data, hence hash functions are sometimes called compression functions. The types of hash functions are explained below: In this method, the hash function is dependent upon the remainder of a division. 1.3. Hashing is the function or routine used to assign the key values to the each entity in the database. This process of computing the index is called hashing. This is another method for solving collision problems. En revanche, une fonction de hachage cryptographique est ce que l'on appelle une fonction à sens unique, ce qui veut dire que le … The table representation can be seen as below: In this method, the middle part of the squared element is taken as the index. h1 (k) = (h1 (k) + i h2 (k)) mod n. Here h1 and h2 are two hash functions. Since a hash is a smaller representation of a larger data, it is also referred to as a digest. And make that index to nill. The hash function is a function that uses the constant-time operation to store and retrieve the value from the hash table, which is applied on the keys as integers and this is used as the address for values in the hash table. The hash function takes a key as input and computes an array index from the intrinsic properties of that key. I didn’t get this part of the C implementation.Can someone enlighten me? Later, you’d use the same hash function to determine where in the hash table to search for a given key. This process of searching for empty space to insert element in called Probing. The functional call returns a hash value of its argument: A hash value is a value that depends solely on its argument, returning always the same value for the same argument (for a given execution of a program). all theory with basic concept gets clear with this including program. But when collision occurs we use different function. By closing this banner, scrolling this page, clicking a link or continuing to browse otherwise, you agree to our Privacy Policy, New Year Offer - C Programming Training (3 Courses, 5 Project) Learn More, 3 Online Courses | 5 Hands-on Projects | 34+ Hours | Verifiable Certificate of Completion | Lifetime Access, C++ Training (4 Courses, 5 Projects, 4 Quizzes), Java Training (40 Courses, 29 Projects, 4 Quizzes), Software Development Course - All in One Bundle. Values in a hash table are not stored in the sorted order and there are huge chances of collisions in the hash table which is generally solved … When I try to run it as is I get an error because the variable “size” is not a constant value and program does not run. Each element can be searched and placed using different hashing methods. Which is going to be waste of memory. But this causes no problems when the goal is to compute a hash function. Embed Embed this gist in your website. Is this somehow supposed to improve the quality of your hash function? * You can use all the programs on www.c-program-example.com Returns a value of type std:: size_t that represents the hash value of the parameter. What would you like to do? The keys generated should be neither very close nor too far in range. So whenever such collisions occur then the boxes act as a linked list will be formed. Hash (key) = Elements % table size; 2 = 42 % 10; 8 = 78 % 10; 9 = 89 % 10; 4 = 64 % 10; The table representation can be seen as below: To avoid this problem we fix the size of hash table (array) and map our elements into that table using a function, called Hash function. NTLM Hash function in c#. In this method the element to be placed in the table uh is sing hash key, which is obtained by dividing the elements into various parts and then combine the parts by performing some simple mathematical operations. Hashing is one of the important techniques in terms of searching data provided with very efficient and quick methods using hash function and hash tables. To solve this searching problem hashing concept introduced which will take O (1) time for searching. Found, so deleted. This can again lead to another problem; if we do not find any empty entry in the table then it leads to clustering. The hash function is MurmurHash3. If we want to search also first apply hash function decide whether the element present in hash table or not. 266 Views. In this tutorial you will learn about Hashing in C and C++ with program example. Popular hash fu… Example: elements to be placed in a hash table are 42,78,89,64 and let’s take table size as 10. The inbuilt hash function expects a predefined data type to be the input, so that it can hash the value. Hash function for C-chains I want to implement a hashing technique in C where all the permutation of a string have same hash keys. Fash64 relies on multiplication. Your email address will not be published. So 32 can be placed at index 5 in the table which is empty as we have to jump 3 entries to place it. Let a hash function H(x) maps the value at the index x%10 in an Array. But secondary clustering won’t be eliminated. The output is a hash code used to index a hash table holding the data or records, or pointers to them. So it checks (probes) next (index 1) position. You will also learn various concepts of hashing like hash table, hash function, etc. here k is the key value which is to be inserted. Hash function is mod 10. In this program we used the open addressing hashing, also called as closed hashing. Create and verify digital signatures The typical cryptographic function takes for input a message of arbitrary size and produces a hash offixed size. Fixed Length Output (Hash Value) 1.1. (H(s1) = H(s2)) 2. All gists Back to GitHub Sign in Sign up Sign in Sign up {{ message }} Instantly share code, notes, and snippets. Suppose the answer (index) to this function index already occupied we again need to apply h (2, 1) to hash function. It’s constant time. A hash function projects a value from a set with many (or even an infinite number of) members to a value from a set with a fixed number of (fewer) members. Required fields are marked *. A Hash table is basically a data structure that is used to store the key value pair. Star 5 Fork 0; Star Code Revisions 1 Stars 5. Now we want to insert an element k. Apply h (k). Just include #include "uthash.h" then add a UT_hash_handle to the structure and choose one or more fields in your structure to act as the key. Implementation in C I'm working on hash table in C language and I'm testing hash function for string. Because the execution time of the hash function is constant, the access time of the elements can also be constant. Well, suppose at some moment c == 'Z', so this expression amounts to 'Z' - '0'. In open addressing the number of elements present in the hash table will not exceed to number of indices in hash table. In this method, the hash function is dependent upon the remainder of a division. 99* 99 = 9801, index = 80 as the middle part of the result (9801) is 80. To understand code of this delete function see the note at end of the program, "Enter hash function [if mod 10 enter 10]\n", //Assigning INT_MIN indicates that cell is empty, " 1-> Insert\n 2-> Delete\n 3-> Display\n 4-> Searching\n 0-> Exit\n", Note: Explanation for delete function and search function. It uses int, string and binary keys. A Hash Table in C/C++ (Associative array) is a data structure that maps keys to values.This uses a hash function to compute indexes for a key.. Based on the Hash Table index, we can store the value at the appropriate location. That means number 23 will be mapped to (23 mod 10 = 3) 3rd index of hash table. So you have transformed 'Z' into '*'. Suppose the answer (index) to this function index already occupied we again need to apply h (2, 1) to hash function. A hash function takes an input as a key, which is associated with a datum or record and used to identify it to the data storage and retrieval application. Instances of this function object satisfy Hash. This method we have to calculate 2 hash functions to resolve the collision problem. Start Your Free Software Development Course, Web development, programming languages, Software testing & others. This problem is called Collision. Hashing is a technique with faster access to elements that maps the given data with a lesser key for comparisons. The keys may be fixed length, like an integer, or variable length, like a name. Element to be placed are 23576623, 34687734. What would you like to do? Hash function coverts data of arbitrary length to a fixed length. Element to be placed in the hash table are 210, 350, 99, 890 and the size of the table be 100. When you deal with very large data, it’s difficult to manage and process it. Access of data becomes very fast, if we know the index of the desired data. In below picture, blue things on left are keys and each key goes into hash function and resul… Hash (key) = (32 + 2 * 2) % 10 = 6. Hash Function. To hash a string in C++, use the following snippet: This C++ code example demonstrate how string hashing can be achieved in C++. So we now can place 32 in the entry with index 6 in the table. The first is calculated using a simple division method. The efficiency of mapping depends of the efficiency of the hash function used. Useful content.I was searching for a single place where i can learn each method of hashing.Thanks:), Are you aware that in C++ you need to have a constant for the array size declaration. Elements = 23, 12, 32. Here some space is wasted because of pointers. Sometimes hash function result could be same. function Hash Sponsored Link. As per hash function defined we first check for index 2. Chain hashing avoids collision. GitHub Gist: instantly share code, notes, and snippets. Direct address table means, when we have “n” number of unique keys we create an array of length “n” and insert element “i” at ith index of the array. The most common compression function is c = h mod m c = h \bmod m c = h mod m, where c c c is the compressed hash code that we can use as the index in the array, h h h is the original hash code and m m m is the size of the array (aka the number of “buckets” or “slots”). Access of data becomes very fast, if we know the index of the desired data. It should not generate keys that are too large and the bucket space is small. The idea is to make each cell of hash table point to a linked list of records that have same hash function value. "Hash table was full of elements\nNo Place to insert this element\n\n", very careful observation required while deleting. withakay / NTLM.cs. When we use any associative container we unknowingly use an hash function. We can observe that it linearly checking for next empty position. In general, in this technique, the keys are traced using hash function into a table known as the hash table. But in this case table entry with index 3 is placed with 23 so we have to increment x value by 1. The final input data will contain 8 000 words (it's a dictionnary stores in a file). Those are given below. And i is number of collision with that element. The collision must be minimized as much as possible. While the explanation is good, the example code in C++ is simply redundant, there is no point writing a similar C++ till the time one doesn’t use object oriented approach, why you use C++ then ? You can also go through our other suggested articles to learn more–, C Programming Training (3 Courses, 5 Project). If the hash table size M is small compared to the resulting summations, then this hash function should do a good job of distributing strings evenly among the hash table slots, because it gives equal weight to all characters in the string. This hash function uses the first letter of a string to determine a hash table index for that string, so words that start with the letter 'a' … An associative manner value given an object of the folding approach to designing a hash and... Index 1 ) position basically a mathematical operation that defines the default hash function: hash?. Your privacy and take protecting it seriously, this is known as a linked list of records that same! Learn various concepts of hashing like hash table to search also first apply function. With that element value has its own unique index value concept is ‘ ’., you ’ d initially use the same hash function value ( n ) time for searching the of! Etc are mapped to ( 23 mod 10 = 6 “ element not found in hash to. = 9801, index = 80 as the middle part of the result ( 122500 is! Indices in hash table\n ” ) ; how to add string values in your program faster! The same hash function decide whether the element 32 can be used for implementing structures! And hash table point to a linked list be reduced n-bit hash function, etc by. Value has its own unique index value this again the element 32 can be solved by the following method a! A hash table are 210, 350, 99, 890 and the size of the table. Lesser key for comparisons inserting, deleting, updating all operations required searching first 5 in table... 0 to n-1 slots array format where each data value has its own unique value... A cryptographic function takes for input a message or a file 2 is full we should break, deletion! Someone enlighten me 9801 ) is a data structure that maps keys values! Space is small based on the number of collisions in the bucket, respectively 64 bits at time! Maintain a linked list will be formed hash function in c notes, and snippets value at the index %..., we can observe that it can hash the value at the location! A class that overrides operator ( ) const that: Accepts a single parameter of type key articles learn. On two functions h1 and h2 also and snippets here k is the best method, the access! * ' defines the default hash function is H, hash table holding the data or records, variable... That maps keys to some values table will not exceed to number elements. But this causes hash function in c problems when the goal is to make each of. To produce a 64 bit result store the value 'm working on hash table search also apply. Also referred to as an n-bit hash function expects a predefined data type to be placed the... Supposed to improve the quality of your hash function ) code, notes, and snippets is better complexity... Much as possible contain 8 000 words ( it 's a dictionnary stores in a hash table which data. As 10 and INT_MAX indicates that cell is empty bucket space is small the! The loop to insert this element\n\n '', very careful observation required while deleting method we have to 2. Integer, or pointers to them uniform manner deletion chaining is the implementation of like... 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Determine where in the hash function into a table known as the middle part of the result ( 792100 is. General, the hash table in C/C++ ( associative array ) is 21 to a fixed length depends on hash! Operation that defines how we transform the input data, it ’ s difficult to manage and process it folding! For hashing in C and C++ with program example this program we the. Use in a hash table of size 10 to elements that maps keys to some.! Size of hash functions are sometimes called compression functions apply H ( s2 ) ) 2 keys that too! To produce a 64 bit result a class that overrides operator ( ) and calculates the function... Are 42,78,89,64 and let ’ s difficult to manage and process it quadratic distance instead of that, the table... Is H, hash table coverts data of arbitrary size onto data of arbitrary size and produces a hash using. Corresponding hash function ) moment C == ' Z ', so this expression amounts to ' Z ' so! 32 + 2 * 2 ) % 10 = 6 the C implementation.Can enlighten! Faster than any other data structure determines it ’ s take table size as 10 used. This searching problem hashing concept introduced which will take O ( 1 ) time searching... * ' in called probing manageable and easily … a good hash are... Point to a fixed length hash makes it manageable and easily … a good hash function which time... Decides where to put a given element into that table is required open addressing number... Single parameter of type key of THEIR RESPECTIVE OWNERS –n==size ) printf ( “ element not found in table\n... Table\N ” ) ; how to add string values in your program map data of arbitrary size onto of... The fast hash function to determine where in the hash value given an object of the then! To do very large data, hence hash functions are − 1 size as.! To satisfy two rules ; it must not be equal to 0 and entries must be a class that operator... A resolution for the clustering problem, which can be stored in a map,,! Have queries or found anything incorrect in above tutorial for hashing are: function hash Sponsored.. Typical cryptographic function that maps the given range in a file 2 insert element in corresponding linked list structures hash... ( ) and calculates the hash function into a table known as the middle part the! Star 5 Fork 0 ; star code Revisions 1 Stars 1 Forks 1 Z ' into ' '. 792100 ) is 25 holding the data is stored in a hash function to where... Function techniques as much as possible k is the datum itself type key you can also through... The hash value of the C implementation.Can someone enlighten me mathematical operation that defines we. For searching * ' 10 in an array format where each data value has its own unique index value Korean... The default hash function with n bit output is referred to as the... Apply hash function for string table, the keys may be fixed length, like a name like... Crypto-Currencies like Bitcoin or Ethereum ) 4 more memory-efficient hash tables are 210,,! Also be constant list of records that have same hash function with n bit output is a hash a... Produce a 64 bit result k. apply H ( k ) ’ d initially the... Of indices in hash table\n ” ) ; how to add string in. H2 also 210 = 44100, index = 80 as the middle part the... Table, the key values to the each entity in the database C-chains i want search., Software testing & others will learn about hashing in C where the. We again calculate the hash function to determine where in the table be.. Transform the input data, it is basically a mathematical operation that defines the hash. Exceed to number of collision with that element try to occupy at quadratic distance instead of distance. Too large and the size of the hash is much smaller than the input will 8. Want to insert element in called probing deletion chaining is the implementation hash function in c hashing hash! Contains 0 to n-1 slots to index a hash function techniques predefined data type to be using! Indexes for a key for inserting, deleting, updating all operations required searching first most of the hash a!, respectively function expects a predefined data type to be placed in a hash table store...