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A veces un programador puede mejorar el rendimiento, al hacer al compilador consciente de los valores constantes en su aplicación. Por ejemplo, en el siguiente segmento de código:

X = X * Y

el compilador generará código muy diferente a tiempo de ejecución si sabe que Y valía 0, 1, 2, or 175.32. Si no conoce el valor para Y , debe generar la secuencia de código más conservadora (no necesariamente la más rápida). Un programador puede comunicarle esos valores a través del uso de la sentencia PARAMETER en FORTRAN. Mediante el empleo de dicha sentencia, el compilador conoce los valores para estas constantes a tiempo de ejecución. Otro ejemplo que hemos visto es:


DO I = 1,10000 DO J=1,IDIM..... ENDDOENDDO

Tras revisar el código, es claro que IDIM era uno de los valores 1, 2, or 3, dependiendo del conjunto de datos en uso. Claramente si el compilador sabía que IDIM valía 1, puede generar un código mucho más simple y rápido.

Remoción de código muerto

A menudo los programas contienen secciones de código muerto que no tiene efecto en las respuestas, y que por tanto puede quitarse. Ocasionalmente, quien escribe el código muerto en el programa es el autor, pero es más común que sea el propio compilador quien lo hace; muchas optimizaciones producen código muerto que hay que barrer después.

Hay dos tipos de código muerto:

  • Instrucciones inalcanzables
  • Instrucciones que producen resultados que jamás se usan

Es fácil que usted escriba código inalcanzable en su programa, al hacer que el flujo de control pase alrededor de él - permanentemente. Si el compilador puede decir que es inalcanzable, lo eliminará. Por ejemplo, es imposible alcanzar la sentencia I = 4 en este programa:


PROGRAM MAIN I = 2WRITE (*,*) I STOPI = 4 WRITE (*,*) IEND

El compilador desechará todo hasta la sentencia STOP , y probablemente le envíe un aviso. El código inalcanzable producido por el compilador durante la optimización se retirará silenciosamente.

Los cálculos con variables locales pueden producir resultados que nunca se usan. Al analizar la definición y usos de una variable, el compilador puede ver qué otras partes de la rutina la referencian. Por supuesto el compilador no puede decir el destino último de las variables que se pasan entre rutinas, externas o comunes, así que tales cálculos siempre se mantienen (siempre y cuando sean alcanzables). Si un compilador realiza un análisis interprocedimental suficiente, puede incluso optimizar variables entre fronteras de rutinas. El análisis interprocedimental puede ser la perdición para los códigos de bancos de pruebas si trata de medir el tiempo de un cálculo sin usar los resultados del mismo. En el siguiente programa, los cálculos que involucran a k no contribuyen en absoluto a la respuesta final, y son buenos candidatos para la eliminación de código muerto:


main () {int i,k; i = k = 1;i += 1; k += 2;printf ("%d\n",i); }

La eliminación de código muerto a menudo produce algunos resultados sorprendentes con bancos de pruebas pobremente escritos. Véase [link] para un ejemplo de este tipo de código.

Questions & Answers

find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
I rally confuse this number And equations too I need exactly help
salma
But this is not salma it's Faiza live in lousvile Ky I garbage this so I am going collage with JCTC that the of the collage thank you my friends
salma
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
hi
salma
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Cómputo de alto rendimiento. OpenStax CNX. Sep 02, 2011 Download for free at http://cnx.org/content/col11356/1.2
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