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Simplify operator classification lookup on Intel

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This commit is contained in:
John Keiser
2020-09-01 06:14:12 -07:00
parent 4c11652808
commit 0925f71987
2 changed files with 66 additions and 12 deletions
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src/westmere/dom_parser_implementation.cpp
+30 -5
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@@ -26,7 +26,32 @@ simdjson_really_inline json_character_block json_character_block::classify(const
// These lookups rely on the fact that anything < 127 will match the lower 4 bits, which is why
// we can't use the generic lookup_16.
auto whitespace_table = simd8<uint8_t>::repeat_16(' ', 100, 100, 100, 17, 100, 113, 2, 100, '\t', '\n', 112, 100, '\r', 100, 100);
auto op_table = simd8<uint8_t>::repeat_16(',', '}', 0, 0, 0xc0u, 0, 0, 0, 0, 0, 0, 0, 0, 0, ':', '{');
// The 6 operators (:,[]{}) have these values:
//
// , 2C
// : 3A
// [ 5B
// { 7B
// ] 5D
// } 7D
//
// If you use | 0x20 to turn [ and ] into { and }, the lower 4 bits of each character is unique.
// We exploit this, using a simd 4-bit lookup to tell us which character match against, and then
// match it (against | 0x20).
//
// To prevent recognizing other characters, everything else gets compared with 0, which cannot
// match due to the | 0x20.
//
// NOTE: Due to the | 0x20, this ALSO treats <FF> and <SUB> (control characters 0C and 1A) like ,
// and :. This gets caught in stage 2, which checks the actual character to ensure the right
// operators are in the right places.
const auto op_table = simd8<uint8_t>::repeat_16(
0, 0, 0, 0,
0, 0, 0, 0,
0, 0, ':', '{', // : = 3A, [ = 5B, { = 7B
',', '}', 0, 0 // , = 2C, ] = 5D, } = 7D
);
// We compute whitespace and op separately. If the code later only use one or the
// other, given the fact that all functions are aggressively inlined, we can
@@ -42,10 +67,10 @@ simdjson_really_inline json_character_block json_character_block::classify(const
// | 32 handles the fact that { } and [ ] are exactly 32 bytes apart
uint64_t op = simd8x64<bool>(
(in.chunks[0] | 32) == simd8<uint8_t>(_mm_shuffle_epi8(op_table, in.chunks[0]-',')),
(in.chunks[1] | 32) == simd8<uint8_t>(_mm_shuffle_epi8(op_table, in.chunks[1]-',')),
(in.chunks[2] | 32) == simd8<uint8_t>(_mm_shuffle_epi8(op_table, in.chunks[2]-',')),
(in.chunks[3] | 32) == simd8<uint8_t>(_mm_shuffle_epi8(op_table, in.chunks[3]-','))
(in.chunks[0] | 32) == simd8<uint8_t>(_mm_shuffle_epi8(op_table, in.chunks[0])),
(in.chunks[1] | 32) == simd8<uint8_t>(_mm_shuffle_epi8(op_table, in.chunks[1])),
(in.chunks[2] | 32) == simd8<uint8_t>(_mm_shuffle_epi8(op_table, in.chunks[2])),
(in.chunks[3] | 32) == simd8<uint8_t>(_mm_shuffle_epi8(op_table, in.chunks[3]))
).to_bitmask();
return { whitespace, op };
}