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Hi I'm writing a shared library and have a two part question:
1. What is the correct (portable?) way of specifying 64-bit constants?
If I need a 64-bit constant set to all 1s, will the following work on all
unit64_t num = 0xffffffffffffffffULL;
2. I have an array of 64 objects that I need to keep track of. I keep
their state (i.e. busy/free) in a 64-bit mask, 1 for busy, 0 for free.
Each object has an id, from 0 to 63. The bit position in the 'state' mask
corresponds to object's id. So if object with id=5 becomes busy, it sets
bit 5 in 'state' variable to 1.
Multiple objects can be busy/free at the same time. I need a fast way to
look at the 'sate' variable and tell which objects are busy, or free.
Below is one algorithm I came up with, can anyone suggest something faster?
uint64_t current_state = state;
for(i=0; i<64; i++)
current_state >>= i;
if(current_state == (0xffffffffffffffffULL >> i))
break; /* all objects are busy */
if((current_state & 0x1U) == 0)
printf("object %d is free\n", i);
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