On Tue, Dec 1, 2015 at 3:05 PM, barret rhoden <[email protected]> wrote:
> > size_t qrand(void)
> > {
> > return ((size_t) rand() << 4) ^ rand();
>
> Was this to make it possible to get rands > (1 << 32) (and thus capable
> of overflow)?
>
Just to make the CPU running in a tight loop like that, to cache the hint
and run for it for the whole lifetime of the test.
> printf("c = %zd\n", c);
>
> What value of c did you get?
>
I already change the code to use something like this for main_test.c
(result did not change much WRT the previous):
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
extern int testovf(size_t a, size_t b);
extern size_t base(void);
size_t num_values = 100000;
size_t qrand(void)
{
size_t v = rand();
if (rand() & 16)
v += (1UL << (sizeof(size_t) * 4));
return v;
}
int main(void)
{
size_t i, j, c;
size_t *vals = calloc(num_values, sizeof(size_t));
for (c = 0; c < num_values; c++) {
do {
vals[c] = qrand();
} while (!vals[c]);
}
c = 0;
for (i = 0; i < 4000; i++) {
for (j = base(); j < num_values; j++) {
c += testovf(vals[j - 1], vals[j]);
}
}
printf("c = %zd\n", c);
return 0;
}
dlibenzi@dlibenzi:/tmp$ time ./test_div
c = 100396000
real 0m3.368s
user 0m3.360s
sys 0m0.004s
dlibenzi@dlibenzi:/tmp$ time ./test_obsd
c = 100396000
real 0m3.752s
user 0m3.748s
sys 0m0.000s
dlibenzi@dlibenzi:/tmp$ time ./test_int128
c = 100396000
real 0m0.564s
user 0m0.563s
sys 0m0.000s
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