Commit a221fc85 authored by Ariel Shtul's avatar Ariel Shtul Committed by Oran Agra
Browse files

[PERF] use snprintf once in addReplyDouble (#11093)

The previous implementation calls `snprintf` twice, the second time used to
'memcpy' the output of the first, which could be a very large string.
The new implementation reserves space for the protocol header ahead
of the formatted double, and then prepends the string length ahead of it.

Measured improvement of simple ZADD of some 25%.

(cherry picked from commit 90223759)
parent 1571907e
......@@ -840,13 +840,29 @@ void addReplyDouble(client *c, double d) {
d > 0 ? 6 : 7);
}
} else {
char dbuf[MAX_LONG_DOUBLE_CHARS+3],
sbuf[MAX_LONG_DOUBLE_CHARS+32];
int dlen, slen;
char dbuf[MAX_LONG_DOUBLE_CHARS+32];
int dlen = 0;
if (c->resp == 2) {
dlen = snprintf(dbuf,sizeof(dbuf),"%.17g",d);
slen = snprintf(sbuf,sizeof(sbuf),"$%d\r\n%s\r\n",dlen,dbuf);
addReplyProto(c,sbuf,slen);
/* In order to prepend the string length before the formatted number,
* but still avoid an extra memcpy of the whole number, we reserve space
* for maximum header `$0000\r\n`, print double, add the resp header in
* front of it, and then send the buffer with the right `start` offset. */
int dlen = snprintf(dbuf+7,sizeof(dbuf) - 7,"%.17g",d);
int digits = digits10(dlen);
int start = 4 - digits;
dbuf[start] = '$';
/* Convert `dlen` to string, putting it's digits after '$' and before the
* formatted double string. */
for(int i = digits, val = dlen; val && i > 0 ; --i, val /= 10) {
dbuf[start + i] = "0123456789"[val % 10];
}
dbuf[5] = '\r';
dbuf[6] = '\n';
dbuf[dlen+7] = '\r';
dbuf[dlen+8] = '\n';
addReplyProto(c,dbuf+start,dlen+9-start);
} else {
dlen = snprintf(dbuf,sizeof(dbuf),",%.17g\r\n",d);
addReplyProto(c,dbuf,dlen);
......
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