"It annoys me that I can't find a way to detect and shift all of the trailing zero bits off in one hit - and that I instead have to detect and shift them off one at a time. "

Depending what platform you're on, check if the __builtin_ctz() function is available to you. The ctz stands for 'count trailing zeros'. Use this to get the number of trailing zeros, then shift them all off at once.

Update: I've added in bitCount(), which allows you to send in the number after stripping off the trailing zeros, and returns a count of the remaining bits.

#include <stdio.h>
#include <math.h>

unsigned int bitCount(int num);

void main () {

    /* Here's your example number, in binary format for visual purpose
+s */

    int num = 0b10100000;

    int noTrailingZeros = num >> __builtin_ctz(num);
   
    unsigned int bitsRemain = bitCount(noTrailingZeros);

    printf(
        "Zeros: %d, No Zeros: %d, Bits remain: %d\n", 
        num, 
        noTrailingZeros, 
        bitsRemain
    );
}

unsigned int bitCount(int num) {
    unsigned int bits = 0;

    while (num) {
        bits++;
        num >>= 1;
    }

    return bits;
}
[download]

Output:

Zeros: 640, No Zeros: 5, Bits remain: 3
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.