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copied!<p>This is slightly different, but I think clearly illustrates the logic involved. I'm working on some MSP430 code in C, and have a timestamp struct very similar to timeval, but with nsecs instead of usecs.</p> <p>This code keeps everything positive, so unsigned ints would work fine, and avoids overflows (I think). It also doesn't modify the timestamps/timevals being passed in, except the result of course.</p> <pre><code>typedef struct timestamp { int32_t secs; int32_t nsecs; } timestamp_t; int timestamp_sub(timestamp_t * x, timestamp_t * y, timestamp_t * result){ // returns 1 if difference is negative, 0 otherwise // result is the absolute value of the difference between x and y negative = 0; if( x->secs > y->secs ){ if( x->nsecs > y->nsecs ){ result->secs = x->secs - y->secs; result->nsecs = x->nsecs - y->nsecs; }else{ result->secs = x->secs - y->secs - 1; result->nsecs = (1000*1000*1000) - y->nsecs + x->nsecs; } }else{ if( x->secs == y->secs ){ result->secs = 0; if( x->nsecs > y->nsecs ){ result->nsecs = x->nsecs - y->nsecs; }else{ negative = 1; result->nsecs = y->nsecs - x->nsecs; } }else{ negative = 1; if( x->nsecs > y->nsecs ){ result->secs = y->secs - x->secs - 1; result->nsecs = (1000*1000*1000) - x->nsecs + y->nsecs; }else{ result->secs = y->secs - x->secs; result->nsecs = y->nsecs - x->nsecs; } } } return negative; } </code></pre>

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