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Avoid multiple branches for checking for trailing sequence

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Kovid Goyal
2024-01-14 09:47:42 +05:30
parent 79f99bb3ad
commit 67d22b0ec6
1 changed files with 17 additions and 8 deletions
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25
kitty/simd-string-impl.h
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@@ -371,18 +371,16 @@ FUNC(utf8_decode_to_esc)(UTF8Decoder *d, const uint8_t *src, size_t src_sz) {
if (src_sz < 4) {
scalar_decode_all(d, src, src_sz); return sentinel_found;
}
// check for an incomplete trailing utf8 sequence
unsigned num_of_trailing_bytes = 0;
if (src[src_sz-1] >= 0xc0) num_of_trailing_bytes = 1; // 2-, 3- and 4-byte characters with only 1 byte left
else if (src[src_sz-2] >= 0xe0) num_of_trailing_bytes = 2; // 3- and 4-byte characters with only 1 byte left
else if (src[src_sz-3] >= 0xf0) num_of_trailing_bytes = 3; // 4-byte characters with only 3 bytes left
src_sz -= num_of_trailing_bytes;
if (src_sz < sizeof(integer_t)) vec = zero_last_n_bytes(vec, sizeof(integer_t) - src_sz);
unsigned num_of_trailing_bytes = 0;
bool check_for_trailing_bytes = true;
// Check if we have pure ASCII and use fast path
debug_register(vec);
int32_t ascii_mask = movemask_epi8(vec);
int32_t ascii_mask;
start_classification:
ascii_mask = movemask_epi8(vec);
if (!ascii_mask) { // no bytes with high bit (0x80) set, so just plain ASCII
FUNC(output_plain_ascii)(d, vec, src_sz);
if (num_of_trailing_bytes) scalar_decode_all(d, src + src_sz, num_of_trailing_bytes);
@@ -414,6 +412,17 @@ FUNC(utf8_decode_to_esc)(UTF8Decoder *d, const uint8_t *src, size_t src_sz) {
counts = add_epi8(counts, shift_right_by_two_bytes(subtract_saturate_epu8(counts, two)));
// counts now contains the number of bytes remaining in each utf-8 sequence of 2 or more bytes
debug_register(counts);
// check for an incomplete trailing utf8 sequence
if (check_for_trailing_bytes && movemask_epi8(cmplt_epi8(one, and_si(counts, cmpeq_epi8(numbered_bytes(), set1_epi8(src_sz - 1)))))) {
// The value of counts at the last byte is > 1 indicating we have a trailing incomplete sequence
check_for_trailing_bytes = false;
if (src[src_sz-1] >= 0xc0) num_of_trailing_bytes = 1; // 2-, 3- and 4-byte characters with only 1 byte left
else if (src_sz > 1 && src[src_sz-2] >= 0xe0) num_of_trailing_bytes = 2; // 3- and 4-byte characters with only 1 byte left
else if (src_sz > 2 && src[src_sz-3] >= 0xf0) num_of_trailing_bytes = 3; // 4-byte characters with only 3 bytes left
src_sz -= num_of_trailing_bytes;
vec = zero_last_n_bytes(vec, sizeof(integer_t) - src_sz);
goto start_classification;
}
// Only ASCII chars should have corresponding byte of counts == 0
if (ascii_mask ^ movemask_epi8(cmpgt_epi8(counts, zero))) goto invalid_utf8;
// The difference between a byte in counts and the next one should be negative,