The TPK algorithm is a simple computer program introduced by Donald Knuth and Luis Trabb Pardo to illustrate the evolution of computer programming languages. In their 1977 work "The Early Development of Programming Languages", Trabb Pardo and Knuth introduced a small program that involved arrays, indexing, mathematical functions, , I/O, conditionals and iteration. They then wrote implementations of the algorithm in several early programming languages to show how such concepts were expressed.
To explain the name "TPK", the authors referred to Grimm's law (which concerns the consonants 't', 'p', and 'k'), the sounds in the word "typical", and their own initials (Trabb Pardo and Knuth). In a talk based on the paper, Knuth said:
In pseudocode:
'''ask''' for 11 numbers to be read into a sequence ''S'' '''reverse''' sequence ''S'' '''for each''' ''item'' '''in''' sequence ''S'' '''call''' a function to do an operation '''if''' ''result'' overflows '''alert''' user '''else''' '''print''' ''result''
The algorithm reads eleven numbers from an input device, stores them in an array, and then processes them in reverse order, applying a user-defined function to each value and reporting either the value of the function or a message to the effect that the value has exceeded some threshold.
real procedure f(t); real t; value t;
f := sqrt(abs(t)) + 5 × t ↑ 3;
for i := 0 step 1 until 10 do read(a[i]);
for i := 10 step -1 until 0 do
begin y := f(a[i]);
if y > 400 then write(i, 'TOO LARGE')
else write(i, y);
end
end TPK.
As many of the early high-level languages could not handle the TPK algorithm exactly, they allow the following modifications:
With these modifications when necessary, the authors implement this algorithm in Konrad Zuse's Plankalkül, in Herman Goldstine and von Neumann's Flowchart, in Haskell Curry's proposed notation, in Short Code of John Mauchly and others, in the Intermediate Program Language of Arthur Burks, in the notation of Heinz Rutishauser, in the language and compiler by Corrado Böhm in 1951–52, in Autocode of Alick Glennie, in the A-2 system of Grace Hopper, in the Laning and Zierler system, in the earliest proposed Fortran (1954) of John Backus, in the Autocode for Mark 1 by Tony Brooker, in ПП-2 of Andrey Ershov, in BACAIC of Mandalay Grems and R. E. Porter, in Kompiler 2 of A. Kenton Elsworth and others, in ADES of E. K. Blum, the Internal Translator of Alan Perlis, in Fortran of John Backus, in ARITH-MATIC and MATH-MATIC from Grace Hopper's lab, in the system of Bauer and Klaus Samelson, and (in addenda in 2003 and 2009) PACT I and TRANSCODE. They then describe what kind of arithmetic was available, and provide a subjective rating of these languages on parameters of "implementation", "readability", "control structures", "data structures", "machine independence" and "impact", besides mentioning what each was the first to do.
double f(double t)
{
int main(void)
{
return sqrt(fabs(t)) + 5 * pow(t, 3);
}
double a[11] = {0}, y;
for (int i = 0; i < 11; i++)
scanf("%lf", &a[i]);
for (int i = 10; i >= 0; i--) {
y = f(a[i]);
if (y > 400)
printf("%d TOO LARGE\n", i);
else
printf("%d %.16g\n", i, y);
}
}
def f(t):
a = float(input())
for i, t in reversed(list(enumerate(a))):
return sqrt(abs(t)) + 5 * t**3
y = f(t)
print(i, "TOO LARGE" if y > 400 else y)
fn f(t: f64) -> Option
fn main() {
let y = t.abs().sqrt() + 5.0 * t.powi(3);
(y <= 400.0).then_some(y)
}
let mut a = [0f64; 11];
for (t, input) in iter::zip(&mut a, io::stdin().lines()) {
*t = input.unwrap().parse().unwrap();
}
a.iter().enumerate().rev().for_each(|(i, &t)| match f(t) {
None => println!("{i} TOO LARGE"),
Some(y) => println!("{i} {y}"),
});
}
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