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Special Code
An Implementation of J


Many primitives contain special code for certain arguments to effect time and/or space savings not available to general arguments. Moreover, some phrases are "recognized" and are supported by special code. For example, the dyad of the hook ($,) is exactly the reshape of APL (denoted by r); its implementation avoids actually ravelling the right argument, and in so doing saves both time and space:

   ts=: 6!:2 , 7!:2@]
   x=: 11 13 17 19 23
   y=: 29 7 23 11 19$'sesquipedalian'

   (x ($,) y) -: x $, y
1

   ts 'x ($,) y'
0.00773981 2.09818e6
   ts 'x $, y'
0.0170125 3.14662e6
Instances of such special code are listed below:
                        
= dyad word-parallel operation on Boolean arguments for the following verbs:
= < <. <: > >. >: +. +: * *. *: ^ ~: | !
<.@f both avoids non-integer intermediate results on extended precision integers
>.@f both avoids non-integer intermediate results on extended precision integers
+ dyad also * and -; on Windows, assembly code for integer arguments for the vector-vector, vector-scalar, and scalar-vector cases
^ dyad x^y works by repeated multiplication if x is real and y is integral
m&|@^ dyad avoids exponentiation for extended precision arguments
m&|@(n&^) monad avoids exponentiation for extended precision arguments
+/ .* dyad special code
-/ .* monad special code in general; special code for square matrices; special code for arrays of 2-by-2 matrices
$, dyad also ($,)"r; avoids ravel
f;.1 both also f;._1 f;.2 f;._2; avoids building argument cells for several verbs: < $ , # [ ] {. {: <@}. <@}: ; also <&}. <@:}. etc.
f;.3 both also f;._3; special code for matrix right arguments
# dyad special code for Boolean left arguments
# i.@# monad also (# i.&#), etc.; avoids i. on Boolean arguments
#: i.@(*/) monad also (#: i.&(*/)), etc.; special code for non-negative integer vectors
=/ monad also < <: > >: +. +: * *. *: ~:; word-parallel operations on Boolean arguments
+/ monad also * and -; on Windows, assembly code for integer arguments
,/ monad linear time
,./ monad linear time
,.&.>/ monad linear time
;/ monad linear time
f/@, monad also f/@:, f/&, f/&:,; avoids ravel
#/. dyad avoids building argument cells
/: both also \:; special code for several data types; special code for arguments with 5 items or less
=/\ monad also +. *. ~:; word-parallel operations on Boolean arguments
+/\ monad also * and -; on Windows, assembly code for integer arguments
=/\. monad also < <: > >: +. +: *. *: ~:; word-parallel operations on Boolean arguments
+/\. monad also * and -; on Windows, assembly code for integer arguments
{ dyad special code for right arguments of several data types; special code for integer left arguments; special code for indexing first two axes
<"1@[ { ] dyad avoids <"1 if left argument is integer array
a=: c}x,y,:z - avoids catenation and lamination; in-place if c is Boolean and a is x or y
y=: x i}y - in-place
f"r both numerous verbs have integrated rank support:
= < <. <: > >. >: + +. +: * *. *: - -: % ^ ~: | |. |: $ , ,. ,: # ! [ ] { {. {: }. }: / /: \ \. \: e. i. i: o. p. p:
? monad also ?.; special code if argument is identically 2
? dyad also ?.; special code if left argument is much smaller than right argument
E. monad special code for Boolean and literal vector arguments
i. monad also i:; special case for length-1 arguments
i. dyad also e. and i:; special code for several data types; special code for i.!.0; special code for arguments with many identical columns


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