[FreecivDev] Re: (PR#1180) [PATCH] cleanup to canvas_pos_to_map_pos
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On Sat, 23 Nov 2002, Ross W. Wetmore wrote:
> It at least recognizes the positive denominator :).
>
> But try this as a way to overcome the "%" antipattern bias ...
>
> /*
> * DIVIDE() divide and round down (== more negative), rather than just
> * divide (round toward 0). It is assumed the divisor is positive.
> * Arguments are used multiple times, so must not have side effects.
> * The full case would be ...
> * DIVIDE_GENERIC(n, d) ( (d) < 0 ? DIVIDE((n), (d)) : DIVIDE((n), (d)) )
> */
> #define DIVIDE(n, d) \
> ( (n) < 0 ? ((n)  (d) + 1) / (d) : (n) / (d) )
>  or 
> ( (n) < 0 ? ((n) + 1) / (d)  1 : (n) / (d) )
Stupid me! I knew there is a way to do it without a % b !!
However, it doesn' make much difference in terms of time:
with
#define DIVIDE_G1(a, b) ( a/b  ( a<0 && (a%b != 0) ) )
test code takes
2.150u 0.000s 0:02.14 100.4% 0+0k 0+0io 75pf+0w
and with
#define DIVIDE_R(n, d) ( n < 0 ? (n  d + 1) / d : n / d )
takes
2.060u 0.000s 0:02.04 100.9% 0+0k 0+0io 75pf+0w
The test code:
for( i = 0; i < 10000000; i++) {
int v, d = (rand()  RAND_MAX/2);
v = DIVIDE(d, 7);
}
 [FreecivDev] Re: (PR#1180) [PATCH] cleanup to canvas_pos_to_map_pos,
Gregory Berkolaiko via RT <=

