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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: why is there not a ipow version of pow?
Date: Sun, 16 Aug 2026 07:33:42 -0700
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bart <bc@freeuk.com> writes:

> [a C version of someone's ipow() function]
>
>  long long int ipow(long long a, int n) {
>     long long int res;
>
>     res = 1;
>     if (n < 0) {
>         res = 0;
>
>     } else if (n == 0) {
>         res = 1;
>
>     } else if (n == 1) {
>         res = a;
>
>     } else if ((n & 1) == 0) {        // n is even
>         res = ipow(a*a, n/2);
>
>     } else {                          // n is odd
>         res = ipow(a*a, (n-1)/2)*a;
>     }
>
>     return res;
>  }

Two observations:

One: one of the recursive calls is not properly tail recursive so
the recursion isn't always optimized out.

Two: it gets wrong answers for in some cases with negative
exponents.