diff options
Diffstat (limited to 'lib/unistr/u8-chr.c')
| -rw-r--r-- | lib/unistr/u8-chr.c | 213 |
1 files changed, 163 insertions, 50 deletions
diff --git a/lib/unistr/u8-chr.c b/lib/unistr/u8-chr.c index 435d1be6..c7779d2a 100644 --- a/lib/unistr/u8-chr.c +++ b/lib/unistr/u8-chr.c @@ -1,5 +1,5 @@ /* Search character in piece of UTF-8 string. - Copyright (C) 1999, 2002, 2006-2007, 2009-2010 Free Software Foundation, + Copyright (C) 1999, 2002, 2006-2007, 2009-2015 Free Software Foundation, Inc. Written by Bruno Haible <bruno@clisp.org>, 2002. @@ -21,68 +21,181 @@ /* Specification. */ #include "unistr.h" +#include <string.h> + uint8_t * u8_chr (const uint8_t *s, size_t n, ucs4_t uc) { - uint8_t c[6]; - if (uc < 0x80) { uint8_t c0 = uc; - for (; n > 0; s++, n--) - { - if (*s == c0) - return (uint8_t *) s; - } + return (uint8_t *) memchr ((const char *) s, c0, n); } - else - switch (u8_uctomb_aux (c, uc, 6)) + + { + uint8_t c[6]; + size_t uc_size; + uc_size = u8_uctomb_aux (c, uc, 6); + + if (n < uc_size) + return NULL; + + /* For multibyte character matching we use a Boyer-Moore like + algorithm that searches for the last byte, skipping multi-byte + jumps, and matches back from there. + + Instead of using a table as is usual for Boyer-Moore, we compare + the candidate last byte s[UC_SIZE-1] with each of the possible + bytes in the UTF-8 representation of UC. If the final byte does + not match, we will perform up to UC_SIZE comparisons per memory + load---but each comparison lets us skip one byte in the input! + + If the final byte matches, the "real" Boyer-Moore algorithm + is approximated. Instead, u8_chr just looks for other cN that + are equal to the final byte and uses those to try realigning to + another possible match. For example, when searching for 0xF0 + 0xAA 0xBB 0xAA it will always skip forward by two bytes, even if + the character in the string was for example 0xF1 0xAA 0xBB 0xAA. + The advantage of this scheme is that the skip count after a failed + match can be computed outside the loop, and that it keeps the + complexity low for a pretty rare case. In particular, since c[0] + is never between 0x80 and 0xBF, c[0] is never equal to c[UC_SIZE-1] + and this is optimal for two-byte UTF-8 characters. */ + switch (uc_size) { case 2: - if (n > 1) - { - uint8_t c0 = c[0]; - uint8_t c1 = c[1]; - - for (n--; n > 0; s++, n--) - { - if (*s == c0 && s[1] == c1) - return (uint8_t *) s; - } - } - break; + { + uint8_t c0 = c[0]; + uint8_t c1 = c[1]; + const uint8_t *end = s + n - 1; + + do + { + /* Here s < end. + Test whether s[0..1] == { c0, c1 }. */ + uint8_t s1 = s[1]; + if (s1 == c1) + { + if (*s == c0) + return (uint8_t *) s; + else + /* Skip the search at s + 1, because s[1] = c1 < c0. */ + s += 2; + } + else + { + if (s1 == c0) + s++; + else + /* Skip the search at s + 1, because s[1] != c0. */ + s += 2; + } + } + while (s < end); + break; + } case 3: - if (n > 2) - { - uint8_t c0 = c[0]; - uint8_t c1 = c[1]; - uint8_t c2 = c[2]; - - for (n -= 2; n > 0; s++, n--) - { - if (*s == c0 && s[1] == c1 && s[2] == c2) - return (uint8_t *) s; - } - } - break; + { + uint8_t c0 = c[0]; + uint8_t c1 = c[1]; + uint8_t c2 = c[2]; + const uint8_t *end = s + n - 2; + size_t skip; + + if (c2 == c1) + skip = 1; + else + skip = 3; + + do + { + /* Here s < end. + Test whether s[0..2] == { c0, c1, c2 }. */ + uint8_t s2 = s[2]; + if (s2 == c2) + { + if (s[1] == c1 && *s == c0) + return (uint8_t *) s; + else + /* If c2 != c1: + Skip the search at s + 1, because s[2] == c2 != c1. + Skip the search at s + 2, because s[2] == c2 < c0. */ + s += skip; + } + else + { + if (s2 == c1) + s++; + else if (s2 == c0) + /* Skip the search at s + 1, because s[2] != c1. */ + s += 2; + else + /* Skip the search at s + 1, because s[2] != c1. + Skip the search at s + 2, because s[2] != c0. */ + s += 3; + } + } + while (s < end); + break; + } case 4: - if (n > 3) - { - uint8_t c0 = c[0]; - uint8_t c1 = c[1]; - uint8_t c2 = c[2]; - uint8_t c3 = c[3]; - - for (n -= 3; n > 0; s++, n--) - { - if (*s == c0 && s[1] == c1 && s[2] == c2 && s[3] == c3) - return (uint8_t *) s; - } - } - break; + { + uint8_t c0 = c[0]; + uint8_t c1 = c[1]; + uint8_t c2 = c[2]; + uint8_t c3 = c[3]; + const uint8_t *end = s + n - 3; + size_t skip; + + if (c3 == c2) + skip = 1; + else if (c3 == c1) + skip = 2; + else + skip = 4; + + do + { + /* Here s < end. + Test whether s[0..3] == { c0, c1, c2, c3 }. */ + uint8_t s3 = s[3]; + if (s3 == c3) + { + if (s[2] == c2 && s[1] == c1 && *s == c0) + return (uint8_t *) s; + else + /* If c3 != c2: + Skip the search at s + 1, because s[3] == c3 != c2. + If c3 != c1: + Skip the search at s + 2, because s[3] == c3 != c1. + Skip the search at s + 3, because s[3] == c3 < c0. */ + s += skip; + } + else + { + if (s3 == c2) + s++; + else if (s3 == c1) + /* Skip the search at s + 1, because s[3] != c2. */ + s += 2; + else if (s3 == c0) + /* Skip the search at s + 1, because s[3] != c2. + Skip the search at s + 2, because s[3] != c1. */ + s += 3; + else + /* Skip the search at s + 1, because s[3] != c2. + Skip the search at s + 2, because s[3] != c1. + Skip the search at s + 3, because s[3] != c0. */ + s += 4; + } + } + while (s < end); + break; + } } - return NULL; + return NULL; + } } |