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#include <stddef.h>
#include "mbstring.h"
#include "rune.h"
int
u8prev(rune *ch, const char8_t **p, const char8_t *start)
{
int off;
const char8_t *s = *p;
ptrdiff_t d = s - start;
if (d <= 0) {
return 0;
} else if (u8byte1(s[-1])) {
if (ch)
*ch = s[-1];
off = 1;
} else if (d > 1 && u8bytec(s[-1]) && u8byte2(s[-2])) {
if (ch)
*ch = ((s[-2] & 0x1F) << 6) | (s[-1] & 0x3F);
off = 2;
} else if (d > 2 && u8bytec(s[-1]) && u8bytec(s[-2]) && u8byte3(s[-3])) {
if (ch) {
*ch = ((s[-3] & 0x0F) << 12) | ((s[-2] & 0x3F) << 6)
| (s[-1] & 0x3F);
}
off = 3;
} else if (d > 3 && u8bytec(s[-1]) && u8bytec(s[-2]) && u8bytec(s[-3])
&& u8byte4(s[-4]))
{
if (ch) {
*ch = ((s[-4] & 0x07) << 18) | ((s[-3] & 0x3F) << 12)
| ((s[-2] & 0x3F) << 6) | (s[-1] & 0x3F);
}
off = 4;
} else {
if (ch)
*ch = RUNE_ERROR;
off = 1;
}
*p -= off;
return off;
}
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