132 lines
9.1 KiB
Factor
132 lines
9.1 KiB
Factor
USING: help.markup help.syntax byte-arrays alien math sequences ;
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IN: specialized-arrays
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HELP: SPECIALIZED-ARRAY:
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{ $syntax "SPECIALIZED-ARRAY: type" }
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{ $values { "type" "a C type" } }
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{ $description "Brings a specialized array for holding values of " { $snippet "type" } " into the vocabulary search path. The generated words are documented in " { $link "specialized-array-words" } "." } ;
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HELP: SPECIALIZED-ARRAYS:
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{ $syntax "SPECIALIZED-ARRAYS: type type type ... ;" }
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{ $values { "type" "a C type" } }
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{ $description "Brings a set of specialized arrays for holding values of each " { $snippet "type" } " into the vocabulary search path. The generated words are documented in " { $link "specialized-array-words" } "." } ;
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{ POSTPONE: SPECIALIZED-ARRAY: POSTPONE: SPECIALIZED-ARRAYS: } related-words
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HELP: direct-slice
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{ $values { "from" integer } { "to" integer } { "seq" "a specialized array" } { "seq'" "a new specialized array" } }
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{ $description "Constructs a new specialized array of the same type as " { $snippet "seq" } " sharing the same underlying memory as the subsequence of " { $snippet "seq" } " from elements " { $snippet "from" } " up to but not including " { $snippet "to" } ". Like " { $link slice } ", raises an error if " { $snippet "from" } " or " { $snippet "to" } " is out of bounds." } ;
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HELP: direct-head
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{ $values { "seq" "a specialized array" } { "n" integer } { "seq'" "a new specialized array" } }
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{ $description "Constructs a new specialized array of the same type as " { $snippet "seq" } " sharing the same underlying memory as the first " { $snippet "n" } " elements of " { $snippet "seq" } ". Like " { $link head } ", raises an error if " { $snippet "n" } " is out of bounds." } ;
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HELP: direct-tail
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{ $values { "seq" "a specialized array" } { "n" integer } { "seq'" "a new specialized array" } }
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{ $description "Constructs a new specialized array of the same type as " { $snippet "seq" } " sharing the same underlying memory as " { $snippet "seq" } " without the first " { $snippet "n" } " elements. Like " { $link tail } ", raises an error if " { $snippet "n" } " is out of bounds." } ;
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HELP: direct-head*
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{ $values { "seq" "a specialized array" } { "n" integer } { "seq'" "a new specialized array" } }
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{ $description "Constructs a new specialized array of the same type as " { $snippet "seq" } " sharing the same underlying memory as " { $snippet "seq" } " without the last " { $snippet "n" } " elements. Like " { $link head* } ", raises an error if " { $snippet "n" } " is out of bounds." } ;
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HELP: direct-tail*
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{ $values { "seq" "a specialized array" } { "n" integer } { "seq'" "a new specialized array" } }
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{ $description "Constructs a new specialized array of the same type as " { $snippet "seq" } " sharing the same underlying memory as the last " { $snippet "n" } " elements of " { $snippet "seq" } ". Like " { $link tail* } ", raises an error if " { $snippet "n" } " is out of bounds." } ;
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{ direct-slice direct-head direct-tail direct-head* direct-tail* } related-words
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ARTICLE: "specialized-array-words" "Specialized array words"
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"The " { $link POSTPONE: SPECIALIZED-ARRAY: } " and " { $link POSTPONE: SPECIALIZED-ARRAYS: } " parsing words generate specialized array types if they haven't been generated already and add the following words to the vocabulary search path, where " { $snippet "T" } " is the C type in question:"
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{ $table
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{ { $snippet "T-array" } { "The class of arrays with elements of type " { $snippet "T" } } }
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{ { $snippet "<T-array>" } { "Constructor for arrays with elements of type " { $snippet "T" } "; stack effect " { $snippet "( len -- array )" } } }
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{ { $snippet "(T-array)" } { "Constructor for arrays with elements of type " { $snippet "T" } ", where the initial contents are uninitialized; stack effect " { $snippet "( len -- array )" } } }
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{ { $snippet "<direct-T-array>" } { "Constructor for arrays with elements of type " { $snippet "T" } " backed by raw memory; stack effect " { $snippet "( alien len -- array )" } } }
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{ { $snippet "T-array{" } { "Literal syntax, consists of a series of values terminated by " { $snippet "}" } } }
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}
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"Behind the scenes, these words are placed in a vocabulary named " { $snippet "specialized-arrays.instances.T" } ", however this vocabulary should not be placed in a " { $link POSTPONE: USING: } " form directly. Instead, always use " { $link POSTPONE: SPECIALIZED-ARRAY: } " or " { $link POSTPONE: SPECIALIZED-ARRAYS: } ". This ensures that the vocabulary can get generated the first time it is needed."
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$nl
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"Additionally, special versions of the standard " { $link <slice> } ", " { $link head } ", and " { $link tail } " sequence operations are provided for specialized arrays to create a new specialized array object sharing storage with a subsequence of an existing array:"
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{ $subsections
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direct-slice
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direct-head
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direct-tail
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direct-head*
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direct-tail*
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} ;
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ARTICLE: "specialized-array-c" "Passing specialized arrays to C functions"
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"If a C function is declared as taking a parameter with a pointer or an array type (for example, " { $snippet "float*" } " or " { $snippet "int[3]" } "), instances of the relevant specialized array can be passed in."
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$nl
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"C type specifiers for array types are documented in " { $link "c-types-specs" } "."
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$nl
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"Here is an example; as is common with C functions, the array length is passed in separately, since C does not offer a runtime facility to determine the array length of a base pointer:"
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{ $code
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"USING: alien.syntax specialized-arrays ;"
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"SPECIALIZED-ARRAY: int"
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"FUNCTION: void process_data ( int* data, int len ) ;"
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"int-array{ 10 20 30 } dup length process_data"
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}
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"Literal specialized arrays, as well as specialized arrays created with " { $snippet "<T-array>" } " and " { $snippet "T >c-array" } " are backed by a " { $link byte-array } " in the Factor heap, and can move as a result of garbage collection. If this is unsuitable, the array can be allocated in unmanaged memory instead."
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$nl
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"In the following example, it is presumed that the C library holds on to a pointer to the array's data after the " { $snippet "init_with_data()" } " call returns; this is one situation where unmanaged memory has to be used instead. Note the use of destructors to ensure the memory is deallocated after the block ends:"
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{ $code
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"USING: alien.syntax specialized-arrays ;"
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"SPECIALIZED-ARRAY: float"
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"FUNCTION: void init_with_data ( float* data, int len ) ;"
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"FUNCTION: float compute_result ( ) ;"
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"["
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" 100 malloc-float-array &free"
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" dup length init_with_data"
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" compute_result"
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"] with-destructors"
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}
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"Finally, sometimes a C library returns a pointer to an array in unmanaged memory, together with a length. In this case, a specialized array can be constructed to view this memory using " { $snippet "<direct-T-array>" } ":"
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{ $code
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"USING: alien.c-types alien.data classes.struct ;"
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""
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"STRUCT: device_info"
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" { id int }"
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" { name char* } ;"
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""
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"FUNCTION: void get_device_info ( int* length ) ;"
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""
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"0 int <ref> [ get_device_info ] keep <direct-int-array> ."
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}
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"For a full discussion of Factor heap allocation versus unmanaged memory allocation, see " { $link "byte-arrays-gc" } "."
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$nl
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"Each specialized array has a " { $slot "underlying" } " slot holding a " { $link byte-array } " with the raw data. Passing a specialized array as a parameter to a C function call will automatically extract the underlying data. To get at the underlying data directly, call the " { $link >c-ptr } " word on a specialized array." ;
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ARTICLE: "specialized-array-math" "Vector arithmetic with specialized arrays"
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"Each specialized array with a numeric type generates specialized versions of the " { $link "math-vectors" } " words. The compiler substitutes calls for these words if it can statically determine input types. The " { $snippet "optimized." } " word in the " { $vocab-link "compiler.tree.debugger" } " vocabulary can be used to determine if this optimization is being performed for a particular piece of code." ;
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ARTICLE: "specialized-array-examples" "Specialized array examples"
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"Let's import specialized float arrays:"
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{ $code "USING: specialized-arrays math.constants math.functions ;" "SPECIALIZED-ARRAY: float" }
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"Creating a float array with 3 elements:"
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{ $code "1.0 [ sin ] [ cos ] [ tan ] tri float-array{ } 3sequence ." }
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"Create a float array and sum the elements:"
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{ $code
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"1000 iota [ 1000 /f pi * sin ] float-array{ } map-as"
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"0.0 [ + ] reduce ."
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} ;
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ARTICLE: "specialized-arrays" "Specialized arrays"
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"The " { $vocab-link "specialized-arrays" } " vocabulary implements fixed-length sequence types for storing machine values in a space-efficient manner without boxing."
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$nl
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"A specialized array type needs to be generated for each element type. This is done with parsing words:"
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{ $subsections
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POSTPONE: SPECIALIZED-ARRAY:
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POSTPONE: SPECIALIZED-ARRAYS:
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}
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"This parsing word adds new words to the search path, documented in the next section."
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{ $subsections
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"specialized-array-words"
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"specialized-array-c"
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"specialized-array-math"
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"specialized-array-examples"
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}
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"The " { $vocab-link "specialized-vectors" } " vocabulary provides a resizable version of this abstraction." ;
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ABOUT: "specialized-arrays"
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