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Speed up the branchless UTF-8 decoder by removing !len #7

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Speed up the branchless UTF-8 decoder by removing !len #7

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7 changes: 6 additions & 1 deletion utf8.h
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Original file line number Diff line number Diff line change
Expand Up @@ -29,19 +29,24 @@ utf8_decode(void *buf, uint32_t *c, int *e)
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 3, 3, 4, 0
};
static const char err_extras[] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1
};
static const int masks[] = {0x00, 0x7f, 0x1f, 0x0f, 0x07};
static const uint32_t mins[] = {4194304, 0, 128, 2048, 65536};
static const int shiftc[] = {0, 18, 12, 6, 0};
static const int shifte[] = {0, 6, 4, 2, 0};

unsigned char *s = buf;
int len = lengths[s[0] >> 3];
int err_extra_len = err_extras[s[0] >> 3];

/* Compute the pointer to the next character early so that the next
* iteration can start working on the next character. Neither Clang
* nor GCC figure out this reordering on their own.
*/
unsigned char *next = s + len + !len;
unsigned char *next = s + len + err_extra_len;

/* Assume a four-byte character and load four bytes. Unused bits are
* shifted out.
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