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[ruby/json] SIMD: Match control char and double quote in one pass

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`c < 32 || c == 34` is equivalent to `c ^ 2 < 33`.

Found in: https://lemire.me/blog/2025/04/13/detect-control-characters-quotes-and-backslashes-efficiently-using-swar/

The gain seem mostly present on micro-benchmark, and even there aren't
very consistent, but it's never slower.

```
== Encoding long string (124001 bytes)
ruby 3.4.2 (2025-02-15 revision https://github.com/ruby/json/commit/d2930f8e7a) +YJIT +PRISM [arm64-darwin24]
Warming up --------------------------------------
               after     5.295k i/100ms
Calculating -------------------------------------
               after     55.796k (± 3.4%) i/s   (17.92 μs/i) -    280.635k in   5.035690s

Comparison:
              before:    49840.7 i/s
               after:    55795.8 i/s - 1.12x  faster
```

https://github.com/ruby/json/commit/034c5debd8
This commit is contained in:
Jean Boussier 2025-04-28 15:23:48 +02:00
parent b7d1e33f26
commit b5beed45a2
1 changed files with 10 additions and 15 deletions
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25
ext/json/generator/generator.c
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@ -320,14 +320,12 @@ static inline FORCE_INLINE uint64_t neon_rules_update(const char *ptr)
{
uint8x16_t chunk = vld1q_u8((const unsigned char *)ptr);
const uint8x16_t lower_bound = vdupq_n_u8(' ');
const uint8x16_t backslash = vdupq_n_u8('\\');
const uint8x16_t dblquote = vdupq_n_u8('\"');
// Trick: c < 32 || c == 34 can be factored as c ^ 2 < 33
// https://lemire.me/blog/2025/04/13/detect-control-characters-quotes-and-backslashes-efficiently-using-swar/
const uint8x16_t too_low_or_dbl_quote = vcltq_u8(veorq_u8(chunk, vdupq_n_u8(2)), vdupq_n_u8(33));
uint8x16_t too_low = vcltq_u8(chunk, lower_bound);
uint8x16_t has_backslash = vceqq_u8(chunk, backslash);
uint8x16_t has_dblquote = vceqq_u8(chunk, dblquote);
uint8x16_t needs_escape = vorrq_u8(too_low, vorrq_u8(has_backslash, has_dblquote));
uint8x16_t has_backslash = vceqq_u8(chunk, vdupq_n_u8('\\'));
uint8x16_t needs_escape = vorrq_u8(too_low_or_dbl_quote, has_backslash);
return neon_match_mask(needs_escape);
}
@ -467,14 +465,11 @@ static inline TARGET_SSE2 FORCE_INLINE int sse2_update(const char *ptr)
{
__m128i chunk = _mm_loadu_si128((__m128i const*)ptr);
const __m128i lower_bound = _mm_set1_epi8(' ');
const __m128i backslash = _mm_set1_epi8('\\');
const __m128i dblquote = _mm_set1_epi8('\"');
__m128i too_low = _mm_cmplt_epu8(chunk, lower_bound);
__m128i has_backslash = _mm_cmpeq_epi8(chunk, backslash);
__m128i has_dblquote = _mm_cmpeq_epi8(chunk, dblquote);
__m128i needs_escape = _mm_or_si128(too_low, _mm_or_si128(has_backslash, has_dblquote));
// Trick: c < 32 || c == 34 can be factored as c ^ 2 < 33
// https://lemire.me/blog/2025/04/13/detect-control-characters-quotes-and-backslashes-efficiently-using-swar/
__m128i too_low_or_dbl_quote = _mm_cmplt_epu8(_mm_xor_si128(chunk, _mm_set1_epi8(2)), _mm_set1_epi8(33));
__m128i has_backslash = _mm_cmpeq_epi8(chunk, _mm_set1_epi8('\\'));
__m128i needs_escape = _mm_or_si128(too_low_or_dbl_quote, has_backslash);
return _mm_movemask_epi8(needs_escape);
}