Rewrite the program while_1 (page 405) so that it runs faster. Use the time builtin to verify the improvement in execution time.

Question

What will be an ideal response?

Answer 1

Speed things up by adding the –f option to the line that calls tcsh to avoid
calling ~/.tcshrc:
$ cat while_2
#!/bin/tcsh -f
...
$ time while_1 1000
The sum is 500500
0.105u 0.083s 0:00.19 94.7% 0+0k 0+0io 0pf+0w
$ time while_2 1000
The sum is 500500
0.092u 0.055s 0:00.14 100.0% 0+0k 0+0io 0pf+0w
You can avoid the while loop altogether by using an equation to speed up
the calculation:
$ cat while_4
#!/bin/tcsh -f
@ sum = ($argv[1] * $argv[1] + $argv[1]) / 2
echo "The sum is $sum"
$ time while_4 1000
The sum is 500500
0.000u 0.002s 0:00.00 0.0% 0+0k 0+0io 0pf+0w