gentoo-overlay/dev-haskell/hashtables/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
	<herd>haskell</herd>
	<herd>proxy-maintainers</herd>
	<maintainer>
		<email>haskell@gentoo.org</email>
	</maintainer>
	<longdescription>
		This package provides a couple of different implementations of mutable hash
		tables in the ST monad, as well as a typeclass abstracting their common
		operations, and a set of wrappers to use the hash tables in the IO monad.
		
		/QUICK START/: documentation for the hash table operations is provided in the
		&quot;Data.HashTable.Class&quot; module, and the IO wrappers (which most users will
		probably prefer) are located in the &quot;Data.HashTable.IO&quot; module.
		
		This package currently contains three hash table implementations:
		
		1. &quot;Data.HashTable.ST.Basic&quot; contains a basic open-addressing hash table
		using linear probing as the collision strategy. On a pure speed basis it
		should currently be the fastest available Haskell hash table
		implementation for lookups, although it has a higher memory overhead
		than the other tables and can suffer from long delays when the table is
		resized because all of the elements in the table need to be rehashed.
		
		2. &quot;Data.HashTable.ST.Cuckoo&quot; contains an implementation of \&quot;cuckoo
		hashing\&quot; as introduced by Pagh and Rodler in 2001 (see
		&lt;http://en.wikipedia.org/wiki/Cuckoo_hashing&gt;). Cuckoo hashing has
		worst-case /O(1)/ lookups and can reach a high \&quot;load factor\&quot;, in which
		the table can perform acceptably well even when more than 90% full.
		Randomized testing shows this implementation of cuckoo hashing to be
		slightly faster on insert and slightly slower on lookup than
		&quot;Data.Hashtable.ST.Basic&quot;, while being more space efficient by about a
		half-word per key-value mapping. Cuckoo hashing, like the basic hash
		table implementation using linear probing, can suffer from long delays
		when the table is resized.
		
		3. &quot;Data.HashTable.ST.Linear&quot; contains a linear hash table (see
		&lt;http://en.wikipedia.org/wiki/Linear_hashing&gt;), which trades some insert
		and lookup performance for higher space efficiency and much shorter
		delays when expanding the table. In most cases, benchmarks show this
		table to be currently slightly faster than @Data.HashTable@ from the
		Haskell base library.
		
		It is recommended to create a concrete type alias in your code when using this
		package, i.e.:
		
		&gt; import qualified Data.HashTable.IO as H
		&gt;
		&gt; type HashTable k v = H.BasicHashTable k v
		&gt;
		&gt; foo :: IO (HashTable Int Int)
		&gt; foo = do
		&gt;	 ht &lt;- H.new
		&gt;	 H.insert ht 1 1
		&gt;	 return ht
		
		Firstly, this makes it easy to switch to a different hash table implementation,
		and secondly, using a concrete type rather than leaving your functions abstract
		in the HashTable class should allow GHC to optimize away the typeclass
		dictionaries.
		
		This package accepts a couple of different cabal flags:
		
		* @unsafe-tricks@, default /ON/. If this flag is enabled, we use some
		unsafe GHC-specific tricks to save indirections (namely @unsafeCoerce#@
		and @reallyUnsafePtrEquality#@. These techniques rely on assumptions
		about the behaviour of the GHC runtime system and, although they&#39;ve been
		tested and should be safe under normal conditions, are slightly
		dangerous. Caveat emptor. In particular, these techniques are
		incompatible with HPC code coverage reports.
		
		* @sse41@, default /OFF/. If this flag is enabled, we use some SSE 4.1
		instructions (see &lt;http://en.wikipedia.org/wiki/SSE4&gt;, first available on
		Intel Core 2 processors) to speed up cache-line searches for cuckoo
		hashing.
		
		* @bounds-checking@, default /OFF/. If this flag is enabled, array accesses
		are bounds-checked.
		
		* @debug@, default /OFF/. If turned on, we&#39;ll rudely spew debug output to
		stdout.
		
		* @portable@, default /OFF/. If this flag is enabled, we use only pure
		Haskell code and try not to use unportable GHC extensions. Turning this
		flag on forces @unsafe-tricks@ and @sse41@ /OFF/.
		
		This package has been tested with GHC 7.0.3, on:
		
		* a MacBook Pro running Snow Leopard with an Intel Core i5 processor,
		running GHC 7.0.3 in 64-bit mode.
		
		* an Arch Linux desktop with an AMD Phenom II X4 940 quad-core processor.
		
		* a MacBook Pro running Snow Leopard with an Intel Core 2 Duo processor,
		running GHC 6.12.3 in 32-bit mode.
		
		Please send bug reports to
		&lt;https://github.com/gregorycollins/hashtables/issues&gt;.
	</longdescription>
	<use>
		<flag name="bounds-checking">if on, use bounds-checking array accesses</flag>
		<flag name="portable">if on, use only pure Haskell code and no GHC extensions.</flag>
		<flag name="unsafe-tricks">turn on unsafe GHC tricks</flag>
	</use>
</pkgmetadata>