Am 19.02.2013 12:42, schrieb Piet van Oostrum:
> Terry Reedy <tjre...@udel.edu> writes:
>> I find this surprising too. I am also surprised that it even works,
>> given that the highest intermediate value is about 57 billion and I do
>> not remember that Basic had infinite precision ints.
>
> That may explain why the Basic version is faster: it gets overflow and
> then it may have taken some shortcuts.
Consider this C program
#include <stdio.h>
int main(void) {
int max = 0;
int m = 0;
long int n;
int count;
int num;
while(m<=1000000) {
m++;
n = m;
count = 0;
while(n != 1) {
count++;
if(n % 2 == 0) {
n = n / 2;
}
else {
n = n*3 + 1;
}
}
if(count > max) {
max = count;
num = m;
}
}
printf("%d, %d\n", num, max);
}
If the line
long int n;
is changed into
unsigned int n;
the program runs in 0.68 sec instead of 0.79, so there is some shortcut.
If changed into
signed int n;
there is a veeery long, perhaps infinite loop.
Greetings
Alexander
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