102 lines
2.9 KiB
C
102 lines
2.9 KiB
C
/*
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* Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
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* The President and Fellows of Harvard College.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* This file is shared between libc and the kernel, so don't put anything
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* in here that won't work in both contexts.
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*/
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#ifdef _KERNEL
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#include <types.h>
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#include <lib.h>
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#else
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#include <stdlib.h>
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#include <string.h>
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#endif
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/*
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* Standard C function: parse a string that represents a decimal integer.
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* Leading whitespace is allowed. Trailing gunk is allowed too. Doesn't
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* really report syntax errors or overflow in any useful way.
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*/
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int
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atoi(const char *s)
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{
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static const char digits[] = "0123456789"; /* legal digits in order */
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unsigned val=0; /* value we're accumulating */
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int neg=0; /* set to true if we see a minus sign */
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/* skip whitespace */
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while (*s==' ' || *s=='\t') {
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s++;
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}
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/* check for sign */
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if (*s=='-') {
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neg=1;
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s++;
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}
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else if (*s=='+') {
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s++;
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}
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/* process each digit */
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while (*s) {
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const char *where;
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unsigned digit;
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/* look for the digit in the list of digits */
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where = strchr(digits, *s);
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if (where==NULL) {
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/* not found; not a digit, so stop */
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break;
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}
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/* get the index into the digit list, which is the value */
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digit = (where - digits);
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/* could (should?) check for overflow here */
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/* shift the number over and add in the new digit */
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val = val*10 + digit;
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/* look at the next character */
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s++;
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}
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/* handle negative numbers */
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if (neg) {
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return -val;
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}
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/* done */
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return val;
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}
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