#2617 introduced an RVV check that only checks if the compiler supports RVV intrinsics without checking if RVV is enabled at compile time.
This has caused compilation failure of node.js on riscv64. Fix it by appending a check for __riscv_vector.
* perf(serialization): SIMD-accelerated string escape position finding
Profiling revealed that string serialization was performing redundant
scanning: first calling fast_needs_escaping() (SIMD scan to check IF
escape needed), then find_next_json_quotable_character() (scalar
byte-by-byte scan to find WHERE).
Profile data from Twitter benchmark showed:
- 54.76% time in atom<std::string> (string serialization)
- 24.85% time in find_next_json_quotable_character (scalar position finding)
This optimization unifies both operations into a single SIMD pass that
directly locates the first quotable character position:
- NEON (ARM64): Uses vceqq_u8/vcltq_u8 for character detection, then
extracts position via __builtin_ctzll on 64-bit vector lanes
- SSE2 (x86-64): Uses _mm_cmpeq_epi8/_mm_subs_epu8 for detection, then
_mm_movemask_epi8 + __builtin_ctz for position extraction
The write_string_escaped function now uses the position finder directly,
eliminating the separate fast_needs_escaping check.
Benchmark results (ARM64, Apple Silicon via Docker with p2996 clang):
- Twitter (string-heavy): 4330 -> 5723 MB/s (+32%)
- CITM (numeric-heavy): ~neutral (expected, few strings)
* perf(serialization): batch integer formatting with 4-digit processing
Profiling with perf annotate revealed that the integer-to-string
conversion loop was a significant hotspot in numeric-heavy workloads.
The original implementation processed 2 digits per iteration:
while (pv >= 100) {
memcpy(write_pointer - 1, &decimal_table[(pv % 100) * 2], 2);
write_pointer -= 2;
pv /= 100;
}
Profile data from CITM benchmark showed:
- 31.20% time in atom<unsigned long> (integer formatting)
- 39.07% of integer formatting time in the 2-byte store instruction
(sturh on ARM64)
- CITM integers average 8.8 digits, meaning 4+ store operations per number
This optimization processes 4 digits per iteration, reducing both store
operations and division count by approximately half for large numbers:
while (pv >= 10000) {
q = pv / 10000;
r = pv % 10000;
r_hi = r / 100; // High 2 digits
r_lo = r % 100; // Low 2 digits
memcpy(write_pointer - 1, &decimal_table[r_lo * 2], 2);
memcpy(write_pointer - 3, &decimal_table[r_hi * 2], 2);
write_pointer -= 4;
pv = q;
}
The division by 10000 compiles to an efficient multiply-high instruction
(umulh on ARM64). Applied to both unsigned and signed integer paths.
Benchmark results (ARM64, Apple Silicon via Docker with p2996 clang):
- Twitter: ~neutral (few integers)
- CITM (numeric-heavy): 2912 -> 3086 MB/s (+6%)
* fix(build): add MSVC compatibility for bit manipulation intrinsics
MSVC does not have __builtin_ctz/__builtin_ctzll. Use _BitScanForward
and _BitScanForward64 from <intrin.h> on MSVC instead.
This fixes the build on all Windows configurations (x64, ARM64, Win32).
* refactor: clean up comments to be implementation-focused
Remove references to specific benchmarks and previous implementations
from code comments. Comments now describe what the code does rather
than historical context.
Daniel Lemire