[ruby/strscan] [CRuby] Optimize `strscan_do_scan()`: Remove
unnecessary use of `rb_enc_get()`
(https://github.com/ruby/strscan/pull/108)
- before: #106
## Why?
In `rb_strseq_index()`, the result of `rb_enc_check()` is used.
-
6c7209cd37/string.c (L4335-L4368)
> enc = rb_enc_check(str, sub);
> return strseq_core(str_ptr, str_ptr_end, str_len, sub_ptr, sub_len,
offset, enc);
-
6c7209cd37/string.c (L4309-L4318)
```C
strseq_core(const char *str_ptr, const char *str_ptr_end, long str_len,
const char *sub_ptr, long sub_len, long offset, rb_encoding *enc)
{
const char *search_start = str_ptr;
long pos, search_len = str_len - offset;
for (;;) {
const char *t;
pos = rb_memsearch(sub_ptr, sub_len, search_start, search_len, enc);
```
## Benchmark
It shows String as a pattern is 1.24x faster than Regexp as a pattern.
```
$ benchmark-driver benchmark/check_until.yaml
Warming up --------------------------------------
regexp 9.225M i/s - 9.328M times in 1.011068s (108.40ns/i)
regexp_var 9.327M i/s - 9.413M times in 1.009214s (107.21ns/i)
string 9.200M i/s - 9.355M times in 1.016840s (108.70ns/i)
string_var 11.249M i/s - 11.255M times in 1.000578s (88.90ns/i)
Calculating -------------------------------------
regexp 9.565M i/s - 27.676M times in 2.893476s (104.55ns/i)
regexp_var 10.111M i/s - 27.982M times in 2.767496s (98.90ns/i)
string 10.060M i/s - 27.600M times in 2.743465s (99.40ns/i)
string_var 12.519M i/s - 33.746M times in 2.695615s (79.88ns/i)
Comparison:
string_var: 12518707.2 i/s
regexp_var: 10111089.6 i/s - 1.24x slower
string: 10060144.4 i/s - 1.24x slower
regexp: 9565124.4 i/s - 1.31x slower
```
https://github.com/ruby/strscan/commit/ff2d7afa19
e73f35ddaf