Hi Mattias,
Could you share your micro benchmark data ?
In my testing, getenv() is very fast.
*) unset PRINTF_EXPONENT_DIGITS
preheat 10000 times, then perform 1000000 times (use 4.67777 seconds)
getenv cost: 4.67777 us
*) set PRINTF_EXPONENT_DIGITS=3
preheat 10000 times, then perform 1000000 times (use 3.41991 seconds)
getenv: 3.41991 us
My CPU is Core2 E6550 at 2.33 GHz.
On Wed, Apr 1, 2015 at 10:26 AM, Dongsheng Song <dongsheng.s...@gmail.com>
wrote:
> Cache getenv() looks a good idea !
> Patch is OK for me.
>
> On Wed, Apr 1, 2015 at 4:16 AM, Mattias Engdegård <matti...@acm.org>
> wrote:
>
>> The functions in the __mingw_printf family are very slow because of the
>> getenv(”PRINTF_EXPONENT_DIGITS”) call that is made every time, even when
>> that information isn’t actually needed.
>>
>> Please consider this patch. It only calls getenv once, caching the result
>> (as is traditionally done in libraries that use environment variables this
>> way). It also only computes the minimum exponent digits when actually
>> needed, at most once per format call.
>>
>> With this patch, __mingw_sprintf(buf, ”x”) goes from being several orders
>> of magnitude slower than the MSVCRT sprintf, to about 66% faster. You don’t
>> see this kind of improvement every day.
>>
>
>
#include <winsock2.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#define NUMBER_PREHEAT 10000
#define NUMBER_PERFORM 1000000
int main(int argc, char *argv[])
{
int i;
double t;
LARGE_INTEGER freq, pc, pc2;
QueryPerformanceFrequency(&freq);
for (i = 0; i < NUMBER_PREHEAT; i++) {
getenv("PRINTF_EXPONENT_DIGITS");
}
QueryPerformanceCounter(&pc);
for (i = 0; i < NUMBER_PERFORM; i++) {
getenv("PRINTF_EXPONENT_DIGITS");
}
QueryPerformanceCounter(&pc2);
t = (pc2.QuadPart - pc.QuadPart) / (double) freq.QuadPart;
fprintf(stdout, "preheat %d times, then perform %d times (use %.5lf seconds)\n", NUMBER_PREHEAT, NUMBER_PERFORM, t);
fprintf(stdout, "getenv cost: %.5lf us\n", t * 1000000.0 / NUMBER_PERFORM);
return 0;
}
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