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Re: Detecting whether UV fits into an NV

by stevieb (Canon)
on Feb 26, 2020 at 01:45 UTC ( #11113420=note: print w/replies, xml ) Need Help??

in reply to Detecting whether UV fits into an NV

"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; }


Zeros: 640, No Zeros: 5, Bits remain: 3

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