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perf: 2.5x faster string split on single-char separators #504

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Merged
cs01 merged 1 commit into from
Apr 13, 2026
Merged

perf: 2.5x faster string split on single-char separators #504

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62 changes: 48 additions & 14 deletions c_bridges/string-ops-bridge.c
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Original file line number Diff line number Diff line change
Expand Up @@ -79,13 +79,26 @@ StringArray *cs_str_split(const char *src, size_t src_len,
}

int32_t part_count = 1;
size_t pos = 0;
while (pos + sep_len <= src_len) {
if (memcmp(src + pos, sep, sep_len) == 0) {
if (sep_len == 1) {
// Fast path: single-char separator uses SIMD memchr
const char c = sep[0];
const char *p = src;
const char *end = src + src_len;
while (p < end) {
const char *hit = (const char *)memchr(p, c, (size_t)(end - p));
if (!hit) break;
part_count++;
pos += sep_len;
} else {
pos++;
p = hit + 1;
}
} else {
size_t pos = 0;
while (pos + sep_len <= src_len) {
if (memcmp(src + pos, sep, sep_len) == 0) {
part_count++;
pos += sep_len;
} else {
pos++;
}
}
}

Expand All @@ -99,21 +112,42 @@ StringArray *cs_str_split(const char *src, size_t src_len,

int32_t idx = 0;
size_t start = 0;
pos = 0;
while (pos + sep_len <= src_len) {
if (memcmp(src + pos, sep, sep_len) == 0) {
size_t plen = pos - start;
if (sep_len == 1) {
// Fast path: single-char separator uses SIMD memchr
const char c = sep[0];
const char *p = src;
const char *end = src + src_len;
while (p < end) {
const char *hit = (const char *)memchr(p, c, (size_t)(end - p));
if (!hit) break;
size_t plen = (size_t)(hit - (src + start));
char *s = pool + pool_off;
memcpy(s, src + start, plen);
s[plen] = '\0';
pool_off += plen + 1;
data[idx] = s;
lens[idx] = (int32_t)plen;
idx++;
start = pos + sep_len;
pos = start;
} else {
pos++;
start = (size_t)(hit - src) + 1;
p = hit + 1;
}
} else {
size_t pos = 0;
while (pos + sep_len <= src_len) {
if (memcmp(src + pos, sep, sep_len) == 0) {
size_t plen = pos - start;
char *s = pool + pool_off;
memcpy(s, src + start, plen);
s[plen] = '\0';
pool_off += plen + 1;
data[idx] = s;
lens[idx] = (int32_t)plen;
idx++;
start = pos + sep_len;
pos = start;
} else {
pos++;
}
}
}
size_t plen = src_len - start;
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