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heuristic to skip chunks of leading whitespace when parsing #881

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heuristic to skip chunks of leading whitespace when parsing #881

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16 changes: 16 additions & 0 deletions ext/json/ext/parser/parser.c
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Original file line number Diff line number Diff line change
Expand Up @@ -607,6 +607,22 @@ json_eat_comments(JSON_ParserState *state)
static inline void
json_eat_whitespace(JSON_ParserState *state)
{
#if defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
// Heuristic: if we see a newline, there may be consecutive of spaces after it.
if (RB_UNLIKELY(state->cursor < state->end && *state->cursor == '\n')) {
state->cursor++;

while (state->cursor+sizeof(uint64_t) <= state->end) {
uint64_t chunk;
memcpy(&chunk, state->cursor, sizeof(uint64_t));
if (chunk != 0x2020202020202020) {
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@byroot byroot Nov 1, 2025

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I think we can do even better.

Unless I'm mistaken, we can get the exact number of consecutive spaces with:

__builtin_ctzll(bytes ^ 0x2020202020202020) / 8

break;
}
state->cursor += sizeof(uint64_t);
}
}
#endif

unsigned char cursor;
while (RB_UNLIKELY(whitespace[cursor = (unsigned char)peek(state)])) {
if (RB_UNLIKELY(cursor == '/')) {
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