blob: 236b970dd2dbb6e87bb7feb1ff0da885822018b5 [file] [log] [blame]
/*
* fast fgets() replacement for log parsing
*
* Copyright 2000-2009 Willy Tarreau <w@1wt.eu>
*
* 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; either version
* 2 of the License, or (at your option) any later version.
*
* This function manages its own buffer and returns a pointer to that buffer
* in order to avoid expensive memory copies. It also checks for line breaks
* 32 bits at a time. It could be improved a lot using mmap() but we would
* not be allowed to replace trailing \n with zeroes and we would be limited
* to small log files on 32-bit machines.
*
*/
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
// return 1 if the integer contains at least one zero byte
static inline unsigned int has_zero(unsigned int x)
{
unsigned int y;
/* Principle: we want to perform 4 tests on one 32-bit int at once. For
* this, we have to simulate an SIMD instruction which we don't have by
* default. The principle is that a zero byte is the only one which
* will cause a 1 to appear on the upper bit of a byte/word/etc... when
* we subtract 1. So we can detect a zero byte if a one appears at any
* of the bits 7, 15, 23 or 31 where it was not. It takes only one
* instruction to test for the presence of any of these bits, but it is
* still complex to check for their initial absence. Thus, we'll
* proceed differently : we first save and clear only those bits, then
* we check in the final result if one of them is present and was not.
*/
y = x;
x = ~x & 0x80808080; /* save and invert bits 7, 15, 23, 31 */
y &= 0x7F7F7F7F; /* clear them */
y -= 0x01010101; /* generate a carry */
y &= x; /* clear the bits that were already set */
return !!y;
}
// return 1 if the argument contains at least one zero byte. See principle above.
static inline unsigned int has_zero64(unsigned long long x)
{
unsigned long long y;
y = x;
x = ~x & 0x8080808080808080ULL; /* save bits 7, 15, 23, 31, 39, 47, 55 and 63 */
y &= 0x7F7F7F7F7F7F7F7FULL; /* clear them */
y -= 0x0101010101010101ULL; /* generate a carry */
y &= x; /* clear the bits that were already set */
return !!y;
}
#define FGETS2_BUFSIZE (256*1024)
const char *fgets2(FILE *stream)
{
static char buffer[FGETS2_BUFSIZE + 9]; // +9 to have zeroes past the end
static char *end = buffer;
static char *line = buffer;
char *next;
int ret;
next = line;
while (1) {
/* this is a speed-up, we read 64 bits at once and check for an
* LF character there. We stop if found then continue one at a
* time.
*/
if (next <= (end-12)) {
/* max 3 bytes tested here */
while ((((unsigned long)next) & 3) && *next != '\n')
next++;
/* maybe we have can skip 4 more bytes */
if ((((unsigned long)next) & 4) && !has_zero(*(unsigned int *)next ^ 0x0A0A0A0AU))
next += 4;
}
/* now next is multiple of 8 or equal to end */
while (next <= (end-68)) {
if (has_zero64(*(unsigned long long *)next ^ 0x0A0A0A0A0A0A0A0AULL))
break;
next += 8;
if (has_zero64(*(unsigned long long *)next ^ 0x0A0A0A0A0A0A0A0AULL))
break;
next += 8;
if (has_zero64(*(unsigned long long *)next ^ 0x0A0A0A0A0A0A0A0AULL))
break;
next += 8;
if (has_zero64(*(unsigned long long *)next ^ 0x0A0A0A0A0A0A0A0AULL))
break;
next += 8;
if (has_zero64(*(unsigned long long *)next ^ 0x0A0A0A0A0A0A0A0AULL))
break;
next += 8;
if (has_zero64(*(unsigned long long *)next ^ 0x0A0A0A0A0A0A0A0AULL))
break;
next += 8;
if (has_zero64(*(unsigned long long *)next ^ 0x0A0A0A0A0A0A0A0AULL))
break;
next += 8;
if (has_zero64(*(unsigned long long *)next ^ 0x0A0A0A0A0A0A0A0AULL))
break;
next += 8;
}
/* maybe we can skip 4 more bytes */
if (!has_zero(*(unsigned int *)next ^ 0x0A0A0A0AU))
next += 4;
/* we finish if needed. Note that next might be slightly higher
* than end here because we might have gone past it above.
*/
while (next < end) {
if (*next == '\n') {
const char *start = line;
*next = '\0';
line = next + 1;
return start;
}
next++;
}
/* we found an incomplete line. First, let's move the
* remaining part of the buffer to the beginning, then
* try to complete the buffer with a new read.
*/
if (line > buffer) {
if (end != line)
memmove(buffer, line, end - line);
end = buffer + (end - line);
next = end;
line = buffer;
} else {
if (end == buffer + FGETS2_BUFSIZE)
return NULL;
}
ret = read(fileno(stream), end, buffer + FGETS2_BUFSIZE - end);
if (ret <= 0) {
if (end == line)
return NULL;
*end = '\0';
return line;
}
end += ret;
/* search for '\n' again */
}
}
#ifdef BENCHMARK
int main() {
const char *p;
unsigned int lines = 0;
while ((p=fgets2(stdin)))
lines++;
printf("lines=%d\n", lines);
return 0;
}
#endif