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34 lines
1.1 KiB
C
34 lines
1.1 KiB
C
#include <stdint.h>
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// Decode one UTF-8 codepoint into cp, return number of bytes to next one.
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// On invalid UTF-8, return -1, and do not change cp.
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// Invalid codepoints are not checked.
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//
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// This code is meant to be inlined, if cp is unused it can be optimized away.
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static int
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u8decode(const char *cs, uint32_t *cp)
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{
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const uint8_t *s = (uint8_t *)cs;
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if (*s == 0) { *cp = 0; return 0; }
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if (*s < 0x80) { *cp = *s; return 1; }
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if (*s < 0xc2) { return -1; } //cont+overlong
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if (*s < 0xe0) { *cp = *s & 0x1f; goto u2; }
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if (*s < 0xf0) {
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if (*s == 0xe0 && (s[1] & 0xe0) == 0x80) return -1; //overlong
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if (*s == 0xed && (s[1] & 0xe0) == 0xa0) return -1; //surrogate
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*cp = *s & 0x0f; goto u3;
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}
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if (*s < 0xf5) {
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if (*s == 0xf0 && (s[1] & 0xf0) == 0x80) return -1; //overlong
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if (*s == 0xf4 && (s[1] > 0x8f)) return -1; //too high
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*cp = *s & 0x07; goto u4;
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}
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return -1;
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u4: if ((*++s & 0xc0) != 0x80) return -1; *cp = (*cp << 6) | (*s & 0x3f);
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u3: if ((*++s & 0xc0) != 0x80) return -1; *cp = (*cp << 6) | (*s & 0x3f);
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u2: if ((*++s & 0xc0) != 0x80) return -1; *cp = (*cp << 6) | (*s & 0x3f);
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return s - (uint8_t *)cs + 1;
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}
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