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libuuid: improve uuid_unparse() performance 

There is 2 improvements:

 * remove useless uuid_unpack,
 * directly print the hexa format from memory without using printf
   we can do this as the bytes order is the network byte order
   https://tools.ietf.org/html/rfc4122#section-4.1.2
   even the spatially unique node identifier(the last 6 bytes)

The improvement is important, some results for 1000000 uuid_unparse calls:

Little Endian Ubuntu:
before took 382623 us
after  took  36740 us

Big Endian OpenBSD:
before took 3138172 us
after  took  180116 us

Signed-off-by: Aurelien LAJOIE <orel@melix.net>
This commit is contained in:
Aurelien LAJOIE 2020-03-26 15:38:27 +01:00 committed by Karel Zak
parent be0044b812
commit 2f81213e26
1 changed files with 21 additions and 24 deletions
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45
libuuid/src/unparse.c
View File

@ -36,41 +36,38 @@
#include "uuidP.h"
static const char *fmt_lower =
"%08x-%04x-%04x-%02x%02x-%02x%02x%02x%02x%02x%02x";
static char const hexdigits_lower[16] = "0123456789abcdef";
static char const hexdigits_upper[16] = "0123456789ABCDEF";
static const char *fmt_upper =
"%08X-%04X-%04X-%02X%02X-%02X%02X%02X%02X%02X%02X";
#ifdef UUID_UNPARSE_DEFAULT_UPPER
#define FMT_DEFAULT fmt_upper
#else
#define FMT_DEFAULT fmt_lower
#endif
static void uuid_unparse_x(const uuid_t uu, char *out, const char *fmt)
static void uuid_fmt(const uuid_t uuid, char *buf, char const fmt[restrict])
{
struct uuid uuid;
char *p = buf;
uuid_unpack(uu, &uuid);
sprintf(out, fmt,
uuid.time_low, uuid.time_mid, uuid.time_hi_and_version,
uuid.clock_seq >> 8, uuid.clock_seq & 0xFF,
uuid.node[0], uuid.node[1], uuid.node[2],
uuid.node[3], uuid.node[4], uuid.node[5]);
for (int i = 0; i < 16; i++) {
if (i == 4 || i == 6 || i == 8 || i == 10) {
*p++ = '-';
}
size_t tmp = uuid[i];
*p++ = fmt[tmp >> 4];
*p++ = fmt[tmp & 15];
}
*p = '\0';
}
void uuid_unparse_lower(const uuid_t uu, char *out)
{
uuid_unparse_x(uu, out, fmt_lower);
uuid_fmt(uu, out, hexdigits_lower);
}
void uuid_unparse_upper(const uuid_t uu, char *out)
{
uuid_unparse_x(uu, out, fmt_upper);
uuid_fmt(uu, out, hexdigits_upper);
}
#ifdef UUID_UNPARSE_DEFAULT_UPPER
void uuid_unparse(const uuid_t uu, char *out)
{
uuid_unparse_x(uu, out, FMT_DEFAULT);
}
__attribute__((alias("uuid_unparse_upper")));
#else
void uuid_unparse(const uuid_t uu, char *out)
__attribute__((alias("uuid_unparse_lower")));
#endif