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#include "rune.h"
#include "utf8.h"
#include "internal/common.h"
const char8_t *
u8prev(rune *ch, const char8_t **p, const char8_t *start)
{
int off;
bool match = true;
const char8_t *s = *p;
ptrdiff_t d = s - start;
if (d <= 0) {
return nullptr;
} else if (U1(s[-1])) {
*ch = s[-1];
off = 1;
} else if (d > 1 && UC(s[-1]) && U2(s[-2])) {
*ch = ((s[-2] & 0x1F) << 6) | (s[-1] & 0x3F);
off = 2;
} else if (d > 2 && UC(s[-1]) && UC(s[-2]) && U3(s[-3])) {
*ch = ((s[-3] & 0x0F) << 12) | ((s[-2] & 0x3F) << 6) | (s[-1] & 0x3F);
off = 3;
} else if (d > 3 && UC(s[-1]) && UC(s[-2]) && UC(s[-3]) && U4(s[-4])) {
*ch = ((s[-4] & 0x07) << 18) | ((s[-3] & 0x3F) << 12)
| ((s[-2] & 0x3F) << 6) | (s[-1] & 0x3F);
off = 4;
} else
match = false;
if (match && u8chkr(*ch))
return *p -= off;
*ch = RUNE_ERROR;
return *p--;
}
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