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perf: Fuse redis_cmd_append_sstr into a single reserve and write #2864

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perf: Fuse redis_cmd_append_sstr into a single reserve and write #2864

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36 changes: 31 additions & 5 deletions library.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1111,11 +1111,37 @@ int redis_cmd_init_sstr(smart_string *str, int num_args, char *keyword, int keyw
* Append a command sequence to a smart_string
*/
int redis_cmd_append_sstr(smart_string *str, char *append, int append_len) {
smart_string_appendc(str, '$');
smart_string_append_long(str, append_len);
smart_string_appendl(str, _NL, sizeof(_NL) - 1);
smart_string_appendl(str, append, append_len);
smart_string_appendl(str, _NL, sizeof(_NL) - 1);
/* Frame one RESP bulk argument ($<len>\r\n<data>\r\n). We format the
* length prefix first so the whole frame size is known, reserve it with a
* single capacity check, then write it directly. This is the per-argument
* hot path for every command, so it avoids the five separate
* bounds-checked smart_string appends the naive form would perform. */
char nbuf[32];
char *digits;
size_t dlen, need;
char *p;

/* A negative length means a caller truncated a >INT_MAX size_t into our
* int parameter; the int-length contract is pervasive in the packing
* layer, so assert it rather than emit a malformed frame. */
ZEND_ASSERT(append_len >= 0);

digits = zend_print_long_to_buf(nbuf + sizeof(nbuf) - 1, append_len);
dlen = (nbuf + sizeof(nbuf) - 1) - digits;
need = 1 + dlen + 2 + (size_t)append_len + 2;

smart_string_alloc(str, need, 0);
p = str->c + str->len;
*p++ = '$';
memcpy(p, digits, dlen);
p += dlen;
*p++ = '\r';
*p++ = '\n';
memcpy(p, append, append_len);
p += append_len;
*p++ = '\r';
*p++ = '\n';
str->len += need;

/* Return our new length */
return str->len;
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