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Commit3c17926

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Speed up printing of integers in snprintf.c.
Since the only possible divisors are 8, 10, and 16, it doesn't costmuch code space to replace the division loop with three copies usingconstant divisors. On most machines, division by a constant can bedone a lot more cheaply than division by an arbitrary value.A microbenchmark testing just snprintf("foo %d") with a 9-digit valueshowed about a 2X speedup for me (tgl). Most of Postgres isn't toodependent on the speed of snprintf, so that the effect in real-worldcases is barely measurable. Still, a cycle saved is a cycle earned.Arjan van de VenDiscussion:https://postgr.es/m/40a4b32a-b841-4667-11b2-a0baedb12714@linux.intel.comDiscussion:https://postgr.es/m/6e51c644-1b6d-956e-ac24-2d1b0541d532@linux.intel.com
1 parent7f580aa commit3c17926

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‎src/port/snprintf.c

Lines changed: 30 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1015,8 +1015,8 @@ fmtint(long long value, char type, int forcesign, int leftjust,
10151015
intminlen,intzpad,intprecision,intpointflag,
10161016
PrintfTarget*target)
10171017
{
1018-
unsigned long longbase;
10191018
unsigned long longuvalue;
1019+
intbase;
10201020
intdosign;
10211021
constchar*cvt="0123456789abcdef";
10221022
intsignvalue=0;
@@ -1075,12 +1075,36 @@ fmtint(long long value, char type, int forcesign, int leftjust,
10751075
vallen=0;
10761076
else
10771077
{
1078-
/* make integer string */
1079-
do
1078+
/*
1079+
* Convert integer to string. We special-case each of the possible
1080+
* base values so as to avoid general-purpose divisions. On most
1081+
* machines, division by a fixed constant can be done much more
1082+
* cheaply than a general divide.
1083+
*/
1084+
if (base==10)
1085+
{
1086+
do
1087+
{
1088+
convert[sizeof(convert)- (++vallen)]=cvt[uvalue %10];
1089+
uvalue=uvalue /10;
1090+
}while (uvalue);
1091+
}
1092+
elseif (base==16)
10801093
{
1081-
convert[sizeof(convert)- (++vallen)]=cvt[uvalue %base];
1082-
uvalue=uvalue /base;
1083-
}while (uvalue);
1094+
do
1095+
{
1096+
convert[sizeof(convert)- (++vallen)]=cvt[uvalue %16];
1097+
uvalue=uvalue /16;
1098+
}while (uvalue);
1099+
}
1100+
else/* base == 8 */
1101+
{
1102+
do
1103+
{
1104+
convert[sizeof(convert)- (++vallen)]=cvt[uvalue %8];
1105+
uvalue=uvalue /8;
1106+
}while (uvalue);
1107+
}
10841108
}
10851109

10861110
zeropad=Max(0,precision-vallen);

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