libgrapheme

unicode string library
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utf8.c (6108B)


      1 /* See LICENSE file for copyright and license details. */
      2 #include <stddef.h>
      3 #include <stdint.h>
      4 
      5 #include "../grapheme.h"
      6 #include "util.h"
      7 
      8 #define BETWEEN(c, l, u) ((c) >= (l) && (c) <= (u))
      9 
     10 /* lookup-table for the types of sequence first bytes */
     11 static const struct {
     12 	uint_least8_t  lower; /* lower bound of sequence first byte */
     13 	uint_least8_t  upper; /* upper bound of sequence first byte */
     14 	uint_least32_t mincp; /* smallest non-overlong encoded codepoint */
     15 	uint_least32_t maxcp; /* largest encodable codepoint */
     16 	/*
     17 	 * implicit: table-offset represents the number of following
     18 	 * bytes of the form 10xxxxxx (6 bits capacity each)
     19 	 */
     20 } lut[] = {
     21 	[0] = {
     22 		/* 0xxxxxxx */
     23 		.lower = 0x00, /* 00000000 */
     24 		.upper = 0x7F, /* 01111111 */
     25 		.mincp = (uint_least32_t)0,
     26 		.maxcp = ((uint_least32_t)1 << 7) - 1, /* 7 bits capacity */
     27 	},
     28 	[1] = {
     29 		/* 110xxxxx */
     30 		.lower = 0xC0, /* 11000000 */
     31 		.upper = 0xDF, /* 11011111 */
     32 		.mincp = (uint_least32_t)1 << 7,
     33 		.maxcp = ((uint_least32_t)1 << 11) - 1, /* 5+6=11 bits capacity */
     34 	},
     35 	[2] = {
     36 		/* 1110xxxx */
     37 		.lower = 0xE0, /* 11100000 */
     38 		.upper = 0xEF, /* 11101111 */
     39 		.mincp = (uint_least32_t)1 << 11,
     40 		.maxcp = ((uint_least32_t)1 << 16) - 1, /* 4+6+6=16 bits capacity */
     41 	},
     42 	[3] = {
     43 		/* 11110xxx */
     44 		.lower = 0xF0, /* 11110000 */
     45 		.upper = 0xF7, /* 11110111 */
     46 		.mincp = (uint_least32_t)1 << 16,
     47 		.maxcp = ((uint_least32_t)1 << 21) - 1, /* 3+6+6+6=21 bits capacity */
     48 	},
     49 };
     50 
     51 size_t
     52 grapheme_decode_utf8(const char *str, size_t len, uint_least32_t *cp)
     53 {
     54 	size_t off, i;
     55 	uint_least32_t tmp;
     56 
     57 	if (cp == NULL) {
     58 		/*
     59 		 * instead of checking every time if cp is NULL within
     60 		 * the decoder, simply point it at a dummy variable here.
     61 		 */
     62 		cp = &tmp;
     63 	}
     64 
     65 	if (str == NULL || len == 0) {
     66 		/* a sequence must be at least 1 byte long */
     67 		*cp = GRAPHEME_INVALID_CODEPOINT;
     68 		return 0;
     69 	}
     70 
     71 	/* identify sequence type with the first byte */
     72 	for (off = 0; off < LEN(lut); off++) {
     73 		if (BETWEEN(((const unsigned char *)str)[0], lut[off].lower,
     74 		            lut[off].upper)) {
     75 			/*
     76 			 * first byte is within the bounds; fill
     77 			 * p with the the first bits contained in
     78 			 * the first byte (by subtracting the high bits)
     79 			 */
     80 			*cp = ((const unsigned char *)str)[0] - lut[off].lower;
     81 			break;
     82 		}
     83 	}
     84 	if (off == LEN(lut)) {
     85 		/*
     86 		 * first byte does not match a sequence type;
     87 		 * set cp as invalid and return 1 byte processed
     88 		 *
     89 		 * this also includes the cases where bits higher than
     90 		 * the 8th are set on systems with CHAR_BIT > 8
     91 		 */
     92 		*cp = GRAPHEME_INVALID_CODEPOINT;
     93 		return 1;
     94 	}
     95 	if (1 + off > len) {
     96 		/*
     97 		 * input is not long enough, set cp as invalid
     98 		 */
     99 		*cp = GRAPHEME_INVALID_CODEPOINT;
    100 
    101 		/*
    102 		 * count the following continuation bytes, but nothing
    103 		 * else in case we have a "rogue" case where e.g. such a
    104 		 * sequence starter occurs right before a NUL-byte.
    105 		 */
    106 		for (i = 0; 1 + i < len; i++) {
    107 			if(!BETWEEN(((const unsigned char *)str)[1 + i],
    108 			            0x80, 0xBF)) {
    109 				break;
    110 			}
    111 		}
    112 
    113 		/*
    114 		 * if the continuation bytes do not continue until
    115 		 * the end, return the incomplete sequence length.
    116 		 * Otherwise return the number of bytes we actually
    117 		 * expected, which is larger than n.
    118 		 */
    119 		return ((1 + i) < len) ? (1 + i) : (1 + off);
    120 	}
    121 
    122 	/*
    123 	 * process 'off' following bytes, each of the form 10xxxxxx
    124 	 * (i.e. between 0x80 (10000000) and 0xBF (10111111))
    125 	 */
    126 	for (i = 1; i <= off; i++) {
    127 		if(!BETWEEN(((const unsigned char *)str)[i], 0x80, 0xBF)) {
    128 			/*
    129 			 * byte does not match format; return
    130 			 * number of bytes processed excluding the
    131 			 * unexpected character as recommended since
    132 			 * Unicode 6 (chapter 3)
    133 			 *
    134 			 * this also includes the cases where bits
    135 			 * higher than the 8th are set on systems
    136 			 * with CHAR_BIT > 8
    137 			 */
    138 			*cp = GRAPHEME_INVALID_CODEPOINT;
    139 			return 1 + (i - 1);
    140 		}
    141 		/*
    142 		 * shift codepoint by 6 bits and add the 6 stored bits
    143 		 * in s[i] to it using the bitmask 0x3F (00111111)
    144 		 */
    145 		*cp = (*cp << 6) | (((const unsigned char *)str)[i] & 0x3F);
    146 	}
    147 
    148 	if (*cp < lut[off].mincp ||
    149 	    BETWEEN(*cp, UINT32_C(0xD800), UINT32_C(0xDFFF)) ||
    150 	    *cp > UINT32_C(0x10FFFF)) {
    151 		/*
    152 		 * codepoint is overlong encoded in the sequence, is a
    153 		 * high or low UTF-16 surrogate half (0xD800..0xDFFF) or
    154 		 * not representable in UTF-16 (>0x10FFFF) (RFC-3629
    155 		 * specifies the latter two conditions)
    156 		 */
    157 		*cp = GRAPHEME_INVALID_CODEPOINT;
    158 	}
    159 
    160 	return 1 + off;
    161 }
    162 
    163 size_t
    164 grapheme_encode_utf8(uint_least32_t cp, char *str, size_t len)
    165 {
    166 	size_t off, i;
    167 
    168 	if (BETWEEN(cp, UINT32_C(0xD800), UINT32_C(0xDFFF)) ||
    169 	    cp > UINT32_C(0x10FFFF)) {
    170 		/*
    171 		 * codepoint is a high or low UTF-16 surrogate half
    172 		 * (0xD800..0xDFFF) or not representable in UTF-16
    173 		 * (>0x10FFFF), which RFC-3629 deems invalid for UTF-8.
    174 		 */
    175 		cp = GRAPHEME_INVALID_CODEPOINT;
    176 	}
    177 
    178 	/* determine necessary sequence type */
    179 	for (off = 0; off < LEN(lut); off++) {
    180 		if (cp <= lut[off].maxcp) {
    181 			break;
    182 		}
    183 	}
    184 	if (1 + off > len || str == NULL || len == 0) {
    185 		/*
    186 		 * specified buffer is too small to store sequence or
    187 		 * the caller just wanted to know how many bytes the
    188 		 * codepoint needs by passing a NULL-buffer.
    189 		 */
    190 		return 1 + off;
    191 	}
    192 
    193 	/* build sequence by filling cp-bits into each byte */
    194 
    195 	/*
    196 	 * lut[off].lower is the bit-format for the first byte and
    197 	 * the bits to fill into it are determined by shifting the
    198 	 * cp 6 times the number of following bytes, as each
    199 	 * following byte stores 6 bits, yielding the wanted bits.
    200 	 *
    201 	 * We do not overwrite the mask because we guaranteed earlier
    202 	 * that there are no bits higher than the mask allows.
    203 	 */
    204 	((unsigned char *)str)[0] = lut[off].lower |
    205 	                            (uint_least8_t)(cp >> (6 * off));
    206 
    207 	for (i = 1; i <= off; i++) {
    208 		/*
    209 		 * the bit-format for following bytes is 10000000 (0x80)
    210 		 * and it each stores 6 bits in the 6 low bits that we
    211 		 * extract from the properly-shifted value using the
    212 		 * mask 00111111 (0x3F)
    213 		 */
    214 		((unsigned char *)str)[i] = 0x80 |
    215 		                            ((cp >> (6 * (off - i))) & 0x3F);
    216 	}
    217 
    218 	return 1 + off;
    219 }