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Diffstat (limited to 'strings/strings_def.h')
| -rw-r--r-- | strings/strings_def.h | 103 |
1 files changed, 103 insertions, 0 deletions
diff --git a/strings/strings_def.h b/strings/strings_def.h new file mode 100644 index 00000000000..6bd8e8f5575 --- /dev/null +++ b/strings/strings_def.h @@ -0,0 +1,103 @@ +#ifndef STRINGS_DEF_INCLUDED +#define STRINGS_DEF_INCLUDED +/* Copyright (C) 2011 Monty Program Ab + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; version 2 of the License. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ + +/* This file is to be include first in all files in the string directory */ + +#include <my_global.h> /* Define standar vars */ +#include "m_string.h" /* Exernal defintions of string functions */ + +/* + We can't use the original DBUG_ASSERT() (which includes _db_flush()) + in the strings library as libdbug is compiled after the the strings + library and we don't want to have strings depending on libdbug which + depends on mysys and strings. +*/ + +#if !defined(DBUG_OFF) +#undef DBUG_ASSERT +#define DBUG_ASSERT(A) assert(A) +#endif + +/* SPACE_INT is a word that contains only spaces */ +#if SIZEOF_INT == 4 +#define SPACE_INT 0x20202020 +#elif SIZEOF_INT == 8 +#define SPACE_INT 0x2020202020202020 +#else +#error define the appropriate constant for a word full of spaces +#endif + +/** + Skip trailing space. + + On most systems reading memory in larger chunks (ideally equal to the size of + the chinks that the machine physically reads from memory) causes fewer memory + access loops and hence increased performance. + This is why the 'int' type is used : it's closest to that (according to how + it's defined in C). + So when we determine the amount of whitespace at the end of a string we do + the following : + 1. We divide the string into 3 zones : + a) from the start of the string (__start) to the first multiple + of sizeof(int) (__start_words) + b) from the end of the string (__end) to the last multiple of sizeof(int) + (__end_words) + c) a zone that is aligned to sizeof(int) and can be safely accessed + through an int * + 2. We start comparing backwards from (c) char-by-char. If all we find is + space then we continue + 3. If there are elements in zone (b) we compare them as unsigned ints to a + int mask (SPACE_INT) consisting of all spaces + 4. Finally we compare the remaining part (a) of the string char by char. + This covers for the last non-space unsigned int from 3. (if any) + + This algorithm works well for relatively larger strings, but it will slow + the things down for smaller strings (because of the additional calculations + and checks compared to the naive method). Thus the barrier of length 20 + is added. + + @param ptr pointer to the input string + @param len the length of the string + @return the last non-space character +*/ + +static inline const uchar *skip_trailing_space(const uchar *ptr,size_t len) +{ + const uchar *end= ptr + len; + + if (len > 20) + { + const uchar *end_words= (const uchar *)(intptr) + (((ulonglong)(intptr)end) / SIZEOF_INT * SIZEOF_INT); + const uchar *start_words= (const uchar *)(intptr) + ((((ulonglong)(intptr)ptr) + SIZEOF_INT - 1) / SIZEOF_INT * SIZEOF_INT); + + DBUG_ASSERT(((ulonglong)(intptr)ptr) >= SIZEOF_INT); + if (end_words > ptr) + { + while (end > end_words && end[-1] == 0x20) + end--; + if (end[-1] == 0x20 && start_words < end_words) + while (end > start_words && ((unsigned *)end)[-1] == SPACE_INT) + end -= SIZEOF_INT; + } + } + while (end > ptr && end[-1] == 0x20) + end--; + return (end); +} +#endif |