System Function DR: Difference between revisions
Sudleyplace (talk  contribs) 
Sudleyplace (talk  contribs) 

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===A Word of Caution===  ===A Word of Caution===  
<p>This  <p>This system function allows you to create special numbers which we don't currently support, such as '''Quiet NaNs''', '''Signalling NaNs''', '''Negative Zero''', and '''Denormals'''. If the system doesn't behave as you expect when using these special numbers, don't be surprised.</p>  
<p>For example,</p>  <p>For example,</p> 
Revision as of 16:16, 12 May 2008
Monadic Function


R is an arbitrary array.  
Z is a numeric scalar which represents the datatype of R. 
The datatypes are encoded with a unique index in the loworder two digits, and the bits per element in the remaining digits:
 100: Boolean, one bit per element
 1601: Character, 16 bits per element
 6402: Integer, 64 bits per element
 6403: Floating Point, 64 bits per element (double precision)
 6404: Arithmetic Progression Array, 64 bits each for the offset and multiplier
 3208: Heterogeneous, 32 bits per element (each is a pointer)
 3210: Nested, 32 bits per element (each is a pointer)
For example,
⎕DR 1 0 1
100
⎕dr ⌈/⍬
6403
⎕dr 2 64⍴1
6404
Dyadic Function


R is an arbitrary array.  
L is an integer scalar datatype (see the table above), or a special value (see below).  
Z is R where each of the values are converted to the datatype indicated by L. 
If the conversion is from a narrower datatype to a wider datatype, there must be exactly enough columns in the right argument to match a multiple of the size of the wider datatype. For example, when converting from character (16bit) to integer (64bit), the last column of the right argument must be a multiple of 4 (= 64/16); otherwise, a LENGTH ERROR is signalled.
6402 ⎕dr 'NARS2000'
23362775258562638 13511005043687474
If the conversion is from a wider datatype to a narrower datatype, each value in the result For example, when converting from integer (64bit) to character (16bit), the last column in the result is the product of last column of the right argument and 4 (= 64/16).
For example,
⍴⎕←1601 ⎕dr 23362775258562638 13511005043687474
NARS2000
8
Keep in mind how Arithmetic Progression Arrays are created and represented as they can fool you. For example, you might try the following to convert from Boolean to integer:
6402 ⎕dr 2 64⍴1
1 0 2 64
However, this doesn't produce the expected result because this particular right argument is actually an APA, not a Boolean vector. What actually happened is the APA was represented as an array with an offset of 1, a multiplier of 0 and a shape of 2 64.
On the other hand, this expression
6402 ⎕dr 2 64⍴1 1
¯1
¯1
produces the expected result because the right argument is now Boolean.
Special Values
There are several special values you may use as a left argument to ⎕dr.
The value 0 displays the datatype of the right argument as a text string so you don't need to remember the datatype numbers.
For example,
0 ⎕dr 'a'
Character (1601): 16 bits per element
0 ⎕dr ⍳12
Arithmetic Progression Array (6404): 64 bit offset + 64 bit multiplier
The values ¯1 and 1 convert between character and floating point. These two arguments make it easy to see the representation of floating point numbers so as to understand better precision and other floating point issues.
For example,
1 ⎕dr 1.1
3FF199999999999A
¯1 ⎕dr '3fd5555555555555'
0.3333333333
1 ⎕dr ¯∞ ∞
FFF0000000000000
7FF0000000000000
The values ¯2 and 2 convert between character and 64bit integer. These two arguments make it easy to see the representation of integers.
For example,
2 ⎕dr ¯1
FFFFFFFFFFFFFFFF
¯2 ⎕dr '7',15⍴'f' — The largest positive integer
9223372036854775807
¯2 ⎕dr '8',15⍴'0' — The smallest negative integer
¯9223372036854775808
2 ⎕dr 9223372036854775807 ¯9223372036854775808
7FFFFFFFFFFFFFFF
8000000000000000
A Word of Caution
This system function allows you to create special numbers which we don't currently support, such as Quiet NaNs, Signalling NaNs, Negative Zero, and Denormals. If the system doesn't behave as you expect when using these special numbers, don't be surprised.
For example,
6403 ⎕dr ¯64↑1
¯0
QNaN←6403 ⎕dr ¯64↑13⍴1
1 ⎕dr QNaN
FFF8000000000000
QNaN=¯∞ ∞
1 1