Let's say I have some 32 bit integer:
000001010100010000100010001001 1 0
(The penultimate bit is bold/italic)
So if I shift it by 2 to the right I get:
00000001010100010000100010001001
Now the penultimate bit is lost. I thought of storing the original value and then using || (logical OR), but that would only work if the penultimate bit is set to 1. What if it's 0?
You'd want bitwise, not logical or; and to preserve the value, you'd need to clear the bit in the new value before inserting the one from the old value:
uint32_t const shift = 2; // number of bits to shift by
uint32_t const mask = (1 << 1); // set of bits to preserve
uint32_t bit_to_save = value & mask;
value >>= shift;
value &= ~mask;
value |= bit_to_save;
or, if you like brevity:
value = ((value >> shift) & ~mask) | (value & mask);
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