c - How to ignore bits in a variable -


i know how delete bits in bit value.

i receive 10 bits value (bit 0 bit 9) , have send variable ignore bit 0, bit 2, bit 4 , bit 6 of received value variable : bit 987531. how can ? heard mask bit don't know how use if know mask 0x55

thank helping me

a solution uses 5 bits be

new_value = ((data & 0x002) >> 1) |             ((data & 0x008) >> 2) |             ((data & 0x020) >> 3) |             ((data & 0x080) >> 4) |             ((data & 0x200) >> 5);

but here solution instead of using fixed number of bits (i.e. 5 in case) uses function allows specify number of bits keep.

it like:

#include <stdio.h> #include <stdlib.h>  unsigned keepoddbits(const unsigned data, const unsigned number_of_bits_to_keep) {   unsigned new_value = 0;   unsigned mask = 0x2;   int i;   (i=0; < number_of_bits_to_keep; ++i)   {     if (mask & data)     {       new_value = new_value | ((mask & data) >> (i + 1));     }     mask = mask << 2;   }   return new_value; }  int main() {   printf("data 0x%x becomes 0x%x\n", 0x3ff, keepoddbits(0x3ff, 5));   printf("data 0x%x becomes 0x%x\n", 0x2aa, keepoddbits(0x2aa, 5));   printf("data 0x%x becomes 0x%x\n", 0x155, keepoddbits(0x155, 5));   return 0; }

will output:

data 0x3ff becomes 0x1f data 0x2aa becomes 0x1f data 0x155 becomes 0x0

changing main request 3 instead of 5 bits, like:

int main() {   printf("data 0x%x becomes 0x%x\n", 0x3ff, keepoddbits(0x3ff, 3));   printf("data 0x%x becomes 0x%x\n", 0x2aa, keepoddbits(0x2aa, 3));   printf("data 0x%x becomes 0x%x\n", 0x155, keepoddbits(0x155, 3));   return 0; }

will output:

data 0x3ff becomes 0x7 data 0x2aa becomes 0x7 data 0x155 becomes 0x0

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