Wincent Colaiuta, Mon, Oct 08, 2007 00:12:17 +0200:
> El 7/10/2007, a las 23:54, Alex Riesen escribió:
>
> >>... All the rest pretty much
> >>was worse than what we started from in that it needed to reevaluate
> >>more conditions and turned out more complicated and obfuscate even to
> >>the human reader.
> >
> >it _is_ smaller. And it is _measurably_ faster on that thing I have at
> >home (and old p4).
>
> Can we see the numbers and the steps used to obtain them? I'm also a
> little bit confused about how an inlined function can lead to a
> smaller executable... or did you just mean lines-of-code?
I did mean the bytes of object code. I never said it produces a
smaller executable.
I compiled with gcc -O2 and -O4, gcc 4.1.2 (Ubuntu 4.1.2-0ubuntu4).
Cut the functions out into their own files and compile them to get the
object code. Compile with -S (assembly) to examine the generated code.
Compare.
#include <stdint.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/time.h>
#include <stdio.h>
#include <string.h>
struct strbuf {
size_t alloc;
size_t len;
char *buf;
};
int strbuf_cmp2(struct strbuf *a, struct strbuf *b)
{
int len = a->len < b->len ? a->len: b->len;
int cmp = memcmp(a->buf, b->buf, len);
if (cmp)
return cmp;
return a->len < b->len ? -1: a->len != b->len;
}
int strbuf_cmp1(struct strbuf *a, struct strbuf *b)
{
int cmp;
if (a->len < b->len) {
cmp = memcmp(a->buf, b->buf, a->len);
return cmp ? cmp : -1;
} else {
cmp = memcmp(a->buf, b->buf, b->len);
return cmp ? cmp : a->len != b->len;
}
}
int main(int argc, char *argv[], char *envp[])
{
struct strbuf s1 = {
.alloc = 0,
.len = 50,
.buf = "01234567890123456789012345678901234567890123456789",
};
struct strbuf s2 = {
.alloc = 0,
.len = 50,
.buf = "0123456789012345678901234567890123456789",
};
struct strbuf s3 = {
.alloc = 0,
.len = 50,
.buf = "0123456789012345678901234567890123456789012345678x",
};
struct timeval tv1, tv2, diff;
unsigned n;
int result;
#define CYCLES 0xffffffffu
strbuf_cmp1(&s1, &s2);
strbuf_cmp1(&s2, &s3);
result = 0;
gettimeofday(&tv1, NULL);
for (n = CYCLES; n--; ) {
result += strbuf_cmp1(&s1, &s2);
result += strbuf_cmp1(&s2, &s3);
result += strbuf_cmp1(&s1, &s3);
result += strbuf_cmp1(&s1, &s1);
result += n;
}
gettimeofday(&tv2, NULL);
timersub(&tv2, &tv1, &diff);
printf("ph=%ld.%ld (%d)\n", diff.tv_sec, diff.tv_usec, result);
strbuf_cmp2(&s1, &s2);
strbuf_cmp2(&s2, &s3);
result = 0;
gettimeofday(&tv1, NULL);
for (n = CYCLES; n--; ) {
result += strbuf_cmp2(&s1, &s2);
result += strbuf_cmp2(&s2, &s3);
result += strbuf_cmp2(&s1, &s3);
result += strbuf_cmp2(&s1, &s1);
result += n;
}
gettimeofday(&tv2, NULL);
timersub(&tv2, &tv1, &diff);
printf("ar=%ld.%ld (%d)\n", diff.tv_sec, diff.tv_usec, result);
return 0;
}
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