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Writing Efficient Code in Dyalog
Roger Hui
Abstract
Part I. Performance Tips
A review of performance tips and rules of thumb useful for writing efficient code.
Part II. Special Code
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.
(These are in addition to idioms.)
We explore special codes with emphasis on the newer constructs.
Part I. Performance Tips
| • | cmpx and wsreq |
| • cmpx ⍵ compares expression timings |
| • 1 1 cmpx ⍵ gets actual times |
| • wsreq ⍵ workspace required |
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| • | work on big chunks of data |
| • amortize fixed costs over more data |
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| • | keep data together |
| • arrays are stored in row-major (ravelled) order |
| • cache misses are expensive |
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| • | order of complexity |
| • know the order of complexity of primitives |
| • avoid O(n*2) operations |
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| • | sorting and searching |
| • sorting is faster than grading |
| • exploit small range integers |
| • x⍳x is useful (and optimized) |
| • use ⎕ct←0 if possible |
| • beware of O(n*2) cases |
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| • | utilities |
| • utilities create centers of gravity |
| • dfns are faster than tradfns |
| • imitate primitives from other languages |
Part II. Special Codes
| • | within a primitive |
| • datatype |
| • boolean data |
| • special but common cases |
| |
| • | Idioms |
| |
| • | operators |
| • ⍤ |
| • ⌸ |
| |
| • | trains |
| • f¨ ⊂ |
| • 1 ⍳⍨ comp |
| • ≢∪ |
References
| [0] |
Hui, Roger,
Performance
Tips, Dyalog ’12, Elsinore, Denmark, 2012-10-14.
|
| [1] |
Hui, Roger,
Exploring
Index-Of, Dyalog ’14, Eastbourne, UK, 2014-09-21.
|
| [2] |
Hui, Roger,
A Speed-Up Story,
Dyalog Blog post, 2014-11-05.
|
| [3] |
Hui, Roger,
Exploring Key,
Dyalog Blog post, 2015-04-13.
|
| [4] |
Hui, Roger,
A Dialog on APL,
Dyalog Blog post 2015-05-18.
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Presented at Dyalog ’15, 2015-09-10.
| created: | 2015-05-24 22:25 |
| updated: | 2015-08-04 19:05 |
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