On 23.11.2015 23:14, William A Rowe Jr wrote:
> L1 cache and other direct effects of cpu internal optimization.
Just what I was thinking. Attached is the same program with one more
pair of functions added (and an easy way to add more "candidates" to the
main-driver). I changed the FOR-loop define to obtain repeatable results:
# Test 1 -- equal strings:
foreach m ( 0 1 2 )
foreach? ./strncasecmp $m 100000000 aaaaaaaaa AAAAAAAAA 7
foreach? end
string.h (nb=100000000, len=7)
time = 6.975845 : res = 0
optimized (nb=100000000, len=7)
time = 1.492197 : res = 0
'A' - 'a' (nb=100000000, len=7)
time = 1.787807 : res = 0
# Test 2 -- immediately-different strings
foreach m ( 0 1 2 )
foreach? ./strncasecmp $m 100000000 aaaaaaaaa xAAAAAAAA 7
foreach? end
string.h (nb=100000000, len=7)
time = 2.527727 : res = -23
optimized (nb=100000000, len=7)
time = 0.406867 : res = -23
'A' - 'a' (nb=100000000, len=7)
time = 0.440320 : res = -23
# Test 3 -- strings different at the very end
foreach m ( 0 1 2 )
foreach? ./strncasecmp $m 100000000 aaaaaaaaa AAAAAAAAx 0
foreach? end
string.h (nb=100000000, len=0)
time = 9.629660 : res = -23
optimized (nb=100000000, len=0)
time = 1.387208 : res = -23
'A' - 'a' (nb=100000000, len=0)
time = 1.754683 : res = -23
The new pair (method 2) does not use the static table, which is likely
to benefit from CPU-cache unfairly in repetitive benchmarks. It is
slower than the table-using method 1 functions. But the two pairs might
be comparable -- or even faster -- in real life.
-mi
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>
#define gettimeofday(X) gettimeofday(X, NULL)
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
#include <limits.h>
/*
* Provide our own known-fast implementation of str[n]casecmp()
* NOTE: ASCII only!
*/
static const unsigned char ucharmap[] = {
0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7,
0x8, 0x9, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf,
0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
0x40, 'a', 'b', 'c', 'd', 'e', 'f', 'g',
'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
'p', 'q', 'r', 's', 't', 'u', 'v', 'w',
'x', 'y', 'z', 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
0x60, 'a', 'b', 'c', 'd', 'e', 'f', 'g',
'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
'p', 'q', 'r', 's', 't', 'u', 'v', 'w',
'x', 'y', 'z', 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
};
int ap_strcasecmp(const char *s1, const char *s2)
{
const unsigned char *ps1 = (const unsigned char *) s1;
const unsigned char *ps2 = (const unsigned char *) s2;
while (*ps1 == *ps2 || ucharmap[*ps1] == ucharmap[*ps2]) {
if (*ps1 == '\0') {
return (0);
}
++ps1;
++ps2;
}
return (ucharmap[*ps1] - ucharmap[*ps2]);
}
int ap_strncasecmp(const char *s1, const char *s2, size_t n)
{
const unsigned char *ps1 = (const unsigned char *) s1;
const unsigned char *ps2 = (const unsigned char *) s2;
while (n--) {
if (*ps1 == *ps2 || ucharmap[*ps1] != ucharmap[*ps2]) {
return (ucharmap[*ps1] - ucharmap[*ps2]);
}
if (*ps1 == '\0') {
break;
}
++ps1;
++ps2;
}
return (0);
}
int mi_strcasecmp(const char *s1, const char *s2)
{
const unsigned char *ps1 = (const unsigned char *) s1;
const unsigned char *ps2 = (const unsigned char *) s2;
for (;;) {
int diff = *ps1 - *ps2;
switch (diff) {
case 0:
break;
case 'A' - 'a':
if (*ps1 <= 'Z' && *ps1 >= 'A')
break;
return 1;
case 'a' - 'A':
if (*ps2 <= 'Z' && *ps2 >= 'A')
break;
return -1;
default:
/* Do, what tolower() would've done */
if (*ps1 <= 'z' && *ps1 >= 'a')
diff -= ('a' - 'A');
if (*ps2 <= 'z' && *ps2 >= 'a')
diff += ('a' - 'A');
return diff;
}
if (*ps1 == '\0') {
break;
}
++ps1;
++ps2;
}
return (0);
}
int mi_strncasecmp(const char *s1, const char *s2, size_t n)
{
const unsigned char *ps1 = (const unsigned char *) s1;
const unsigned char *ps2 = (const unsigned char *) s2;
while (n--) {
int diff = *ps1 - *ps2;
switch (diff) {
case 0:
break;
case 'A' - 'a':
if (*ps1 <= 'Z' && *ps1 >= 'A')
break;
return 1;
case 'a' - 'A':
if (*ps2 <= 'Z' && *ps2 >= 'A')
break;
return -1;
default:
/* Do, what tolower() would've done */
if (*ps1 <= 'z' && *ps1 >= 'a')
diff -= ('a' - 'A');
if (*ps2 <= 'z' && *ps2 >= 'a')
diff += ('a' - 'A');
return diff;
}
if (*ps1 == '\0') {
break;
}
++ps1;
++ps2;
}
return (0);
}
#define PROG argv[0]
#define METHOD argv[1]
#define NB argv[2]
#define S1 argv[3]
#define S2 argv[4]
#define LEN argv[5]
/* The ++ are here to try to prevent some optimization done by gcc */
#define FOR for (i=0; i<nb; i++)
int main(int argc, char *argv[])
{
int64_t diff;
struct rusage rus, rue;
int i, len, nb, method;
int res = 0;
struct {
const char *label;
int (*cmp)(const char *, const char *);
int (*ncmp)(const char *, const char *, size_t);
} methods[] = {
{ "string.h", strcasecmp, strncasecmp },
{ "optimized", ap_strcasecmp, ap_strncasecmp },
{ "'A' - 'a'", mi_strcasecmp, mi_strncasecmp }
};
if (argc < 6) {
fprintf(stderr, "%s <0=std ; 1=optimized> <nb iter> S1 S2 <nb
char to compare or 0>\n", PROG);
return EX_USAGE;
}
len = atoi(LEN);
nb = atoi(NB);
method = atoi(METHOD);
if (method < 0 || method >= sizeof(methods)/sizeof(methods[0])) {
fprintf(stderr, "Invalid method requested (``%s''?)\n",
METHOD);
return EX_USAGE;
}
printf("%s (nb=%d, len=%d)\n", methods[method].label, nb, len);
getrusage(RUSAGE_SELF, &rus);
if (len == 0) {
FOR {
res |= methods[method].cmp(S1, S2);
}
} else {
FOR {
res |= methods[method].ncmp(S1, S2, len);
}
}
getrusage(RUSAGE_SELF, &rue);
diff = (int64_t)rue.ru_utime.tv_sec * 1000000L + rue.ru_utime.tv_usec;
diff -= (int64_t)rus.ru_utime.tv_sec * 1000000L + rus.ru_utime.tv_usec;
/* really use the result of the function */
printf("time = %lld.%.6lld : res = %d\n",
(long long)diff / 1000000L,
(long long)diff % 1000000L,
res);
return 0;
}
