### Speed of The Evaluation vs. Length of The Names of The Variables.

; Newlisp is an interpreter; so one question bothered me: does the
; length of the variables influence the speed of the evaluation?
; Is my program any faster if I use, say, x instead of xxx? It
; should be at least bit faster. But how much faster?

; I wrote the program that evaluates essentially same expression,
; but with different variables;

; (for (a 1 10) ...
; (for (aa 1 10) ...
; (for (aaaa 1 10) ...

; and so forth.

; On my surprise, there are no noticeable differences in the
; time required for evaluation. Here are the results:

; length(var)=1, length(expression)=35, time=340
; length(var)=2, length(expression)=38, time=339
; length(var)=4, length(expression)=44, time=336
; length(var)=8, length(expression)=56, time=364
; length(var)=16, length(expression)=80, time=359
; length(var)=32, length(expression)=128, time=350
; length(var)=64, length(expression)=224, time=354
; length(var)=128, length(expression)=416, time=364
; length(var)=256, length(expression)=800, time=352
; length(var)=512, length(expression)=1568, time=337
; length(var)=1024, length(expression)=3104, time=332
; length(var)=2048, length(expression)=6176, time=360
; length(var)=4096, length(expression)=12320, time=342
; length(var)=8192, length(expression)=24608, time=337
; length(var)=16384, length(expression)=49184, time=337
; length(var)=32768, length(expression)=98336, time=351
; length(var)=65536, length(expression)=196640, time=338
; length(var)=131072, length(expression)=393248, time=339
; length(var)=262144, length(expression)=786464, time=341
; length(var)=524288, length(expression)=1572896, time=356
; length(var)=1048576, length(expression)=3145760, time=348
; length(var)=2097152, length(expression)=6291488, time=341
; length(var)=4194304, length(expression)=12582944, time=336
; length(var)=8388608, length(expression)=25165856, time=347

; And i did it for another expression, this time bit more
; complicated, again, there is no visible influence of the
; length of the variable and length of the expression on
; evaluation time.

; length(var)=1, length(expression)=79, time=1565
; length(var)=2, length(expression)=87, time=1562
; length(var)=4, length(expression)=103, time=1574
; length(var)=8, length(expression)=135, time=1559
; length(var)=16, length(expression)=199, time=1568
; length(var)=32, length(expression)=327, time=1557
; length(var)=64, length(expression)=583, time=1555
; length(var)=128, length(expression)=1095, time=1545
; length(var)=256, length(expression)=2119, time=1544
; length(var)=512, length(expression)=4167, time=1554
; length(var)=1024, length(expression)=8263, time=1564
; length(var)=2048, length(expression)=16455, time=1553
; length(var)=4096, length(expression)=32839, time=1560
; length(var)=8192, length(expression)=65607, time=1557
; length(var)=16384, length(expression)=131143, time=1559
; length(var)=32768, length(expression)=262215, time=1557
; length(var)=65536, length(expression)=524359, time=1554
; length(var)=131072, length(expression)=1048647, time=1539
; length(var)=262144, length(expression)=2097223, time=1521
; length(var)=524288, length(expression)=4194375, time=1527
; length(var)=1048576, length(expression)=8388679, time=1550
; length(var)=2097152, length(expression)=16777287, time=1536
; length(var)=4194304, length(expression)=33554503, time=1534
; length(var)=8388608, length(expression)=67108935, time=1535

(setq varname 'a)
(for (i 1 24)
(set 'expr
(expand '(for (varname 1 100)
(+ (- varname 1) (- varname 2)))
'varname))
(set 'evtime
(time (eval (eval expr)) 10000))

(print "length(var)=" (length (string varname)))
(print ", length(expression)=" (length (string expr)))
(println ", time=" evtime)

(setq varname (sym (dup (string varname) 2))))

(println)

(setq varname1 'a)
(setq varname2 'b)
(for (i 1 24)
(set 'expr
(expand '(begin (set 'varname1
(lambda(varname2)
(if (< varname2 3)
1
(+ (varname1 (- varname2 1))
(varname1 (- varname2 2))))))
(varname1 12))
'varname1
'varname2))
(set 'evtime
(time (eval expr) 10000))

(print "length(var)=" (length (string varname1)))
(print ", length(expression)=" (length (string expr)))
(println ", time=" evtime)

(setq varname1 (sym (dup (string varname1) 2)))
(setq varname2 (sym (dup (string varname2) 2))))

#### 1 comment:

1. Before newLISP evaluates an expression, the reader compiles each expression to an internal tree structure of lisp cells, where a variable is just a memory pointer to a symbol.

Any difference in execution time would only be visible during source code loading or during execution of newLISP functions, which itself translate variable names when creating symbols, like (sym ...).