timecop:
> Does anyone on this list honestly believe that in 2010 a difference
> between "slow emulated 64bit" and "native 64bit" integer on any
> hardware made in the last decade is going to be even noticeable.
...
You have to test to know, and you can get a first impression by
this simplistic test:
$ cat testb.c
#include <math.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/time.h>
#define TESTIT(op, str) \
gettimeofday(&sta, NULL); \
for (ix = 0; ix < 1000000000; ix++) { \
(op); \
} \
gettimeofday(&end, NULL); \
timersub(&end, &sta, &diff); \
printf(str " %ld.%06ld\n", diff.tv_sec, diff.tv_usec);
int main(void) {
struct timeval sta;
struct timeval end;
struct timeval diff;
int32_t xi;
int64_t xl;
double xd;
int ix;
double sqrt2 = sqrt(2);
xd = xl = xi = 0;
printf("Loop time for x++\n");
TESTIT(xi++, "int32_t");
TESTIT(xl++, "int64_t");
TESTIT(xd++, "double ");
xd = xl = xi = 1;
printf("\nLoop time for x *= 5\n");
TESTIT(xi *= 5, "int32_t");
TESTIT(xl *= 5, "int64_t");
TESTIT(xd *= 5, "double ");
xd = xl = xi = 1;
printf("\nLoop time for x *= sqrt2\n");
TESTIT(xi *= sqrt2, "int32_t");
TESTIT(xl *= sqrt2, "int64_t");
TESTIT(xd *= sqrt2, "double ");
return 0;
}
$ gcc -lm testb.c -o testb
$ ./testb
Loop time for x++
int32_t 3.600433
int64_t 4.301995
double 7.725700
Loop time for x *= 5
int32_t 5.205665
int64_t 8.391968
double 7.733138
Loop time for x *= sqrt2
int32_t 22.415493
int64_t 22.022103
double 7.911313
$ grep 'name' /proc/cpuinfo
model name : AMD Athlon(TM) XP 2400+
$
On another box:
$ ./testb
Loop time for x++
int32_t 2.429795
int64_t 2.664763
double 5.269211
Loop time for x *= 5
int32_t 2.641352
int64_t 4.079825
double 5.107343
Loop time for x *= sqrt2
int32_t 14.814515
int64_t 14.814356
double 4.951645
$ grep 'name' /proc/cpuinfo | head -1
model name : AMD Phenom(tm) II X4 925 Processor
$
As you can see from above:
int32_t is fastest for simple + and *
double has an almost constant operator time
The performance choise is between int32_t and double:
for "+" int32_t wins with a factor 2, and for "*" double wins
with a factor 3.
What operation is the most common in pcb ?
Regards,
/Karl Hammar
---------
Aspö Data
Lilla Aspö 148
S-742 94 Östhammar
Sweden
+46 173 140 57
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