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Optimizations for better read performance

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fgets() now copies as much data from the read buffer as possible, falling back onto the __getc() macro only as a last resort. This should help greatly when reading long lines since the overhead of calling __getc() goes away.
This commit is contained in:
obarthel
2019-08-24 13:50:41 +02:00
parent 5f14118d73
commit 3f21e90fca
1 changed files with 51 additions and 4 deletions
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55
library/stdio_fgets.c
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@ -1,10 +1,8 @@
/*
* $Id: stdio_fgets.c,v 1.6 2006-01-08 12:04:24 obarthel Exp $
*
* :ts=4
*
* Portable ISO 'C' (1994) runtime library for the Amiga computer
* Copyright (c) 2002-2015 by Olaf Barthel <obarthel (at) gmx.net>
* Copyright (c) 2002-2019 by Olaf Barthel <obarthel (at) gmx.net>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@ -46,6 +44,7 @@
char *
fgets(char *s,int n,FILE *stream)
{
struct iob * file = (struct iob *)stream;
char * result = s;
int c;
@ -98,8 +97,54 @@ fgets(char *s,int n,FILE *stream)
/* One off for the terminating '\0'. */
n--;
while(n-- > 0)
while(n > 0)
{
/* If there is data in the buffer, try to copy it directly
into the string buffer. If there is a line feed in the
buffer, too, try to conclude the read operation. */
if(file->iob_BufferPosition < file->iob_BufferReadBytes)
{
const unsigned char * buffer = &file->iob_Buffer[file->iob_BufferPosition];
size_t num_bytes_in_buffer;
const unsigned char * lf;
/* Copy only as much data as will fit into the string buffer. */
num_bytes_in_buffer = file->iob_BufferReadBytes - file->iob_BufferPosition;
if(num_bytes_in_buffer > (size_t)n)
num_bytes_in_buffer = n;
/* Try to find a line feed character which could conclude
the read operation if the remaining buffer data, including
the line feed character, fit into the string buffer. */
lf = (unsigned char *)memchr(buffer, '\n', num_bytes_in_buffer);
if(lf != NULL)
{
size_t num_characters_in_line = lf + 1 - buffer;
/* Copy the remainder of the read buffer into the
string buffer, including the terminating line
feed character. */
memmove(s, buffer, num_characters_in_line);
file->iob_BufferPosition += num_characters_in_line;
/* And that concludes the line read operation. */
break;
}
memmove(s, buffer, num_bytes_in_buffer);
s += num_bytes_in_buffer;
file->iob_BufferPosition += num_bytes_in_buffer;
/* Stop if the string buffer has been filled. */
n -= num_bytes_in_buffer;
if(n == 0)
break;
}
/* Read the next buffered character; this will refill the read
buffer, if necessary. */
c = __getc(stream);
if(c == EOF)
{
@ -124,6 +169,8 @@ fgets(char *s,int n,FILE *stream)
if(c == '\n')
break;
n--;
}
(*s) = '\0';