98 lines
1.9 KiB
C
98 lines
1.9 KiB
C
#include <unistd.h>
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#include "libio.h"
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/* Backups of standard library systems for the odd scenario where there is no
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* standard library but there is the write(2) system call. */
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#if defined USE_SYSTEM_STRING_H
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# include <string.h>
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# define _strlen strlen
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#else
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/* Normally in <string.h> */
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static int
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_strlen(char *s){
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int i;
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for(i = 0; s[i] != '\0'; ++i);
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return i;
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}
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#endif
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#if defined USE_SYSTEM_CTYPE_H
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# include <ctype.h>
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# define _isdigit isdigit
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#else
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/* Normally in <ctype.h> */
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static int
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_isdigit(int c){
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return c >= '0' && c <= '9';
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}
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#endif
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/* Wrappers around write(2) */
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static int _write(int fd, char *s, int n);
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static int _write1(int fd, int c);
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/* Wrapper around write(2) - keeps re-running write(2) until the operation
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* succeeds in full. Usually unnecessary but still good. */
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static int
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_write(int fd, char *s, int n){
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int i;
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for(
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i = 0;
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i < n;
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i += write(fd, s+i, n-i)
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);
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return i;
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}
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/* For writing a single character. To optimize for speed, functions should
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* allocate a buffer and add to that buffer before write(2)ing the buffer out
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* in a single system call. However sometimes cheap tricks are as effective. */
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static int
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_write1(int fd, int c){
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while(write(fd, &c, 1) != 1);
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return 1;
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}
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int
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fdprint(int fd, char *s){
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return _write(fd, s, _strlen(s));
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}
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int
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fdputs(int fd, char *s){
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int i;
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int r;
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i = _strlen(s);
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/* RACE CONDITION */
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/* This leaves s as an invalid string while the write(2) syscall is
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* performed, which can take a non-trivial amount of time. This
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* implementation is unsuitable when s is shared between threads or
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* whatever the CS term for that is. */
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s[i] = '\n';
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r = _write(fd, s, i + 1);
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s[i] = '\0';
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return r;
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}
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/* Another possible implementation would take char **s and leave *s at the next
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* non-digit. But that's less simple; just while(isdigit(*s)) ++s;. */
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unsigned int
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parse_uint(char *s){
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unsigned int r;
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for(
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r = 0;
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_isdigit(*s);
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r = r * 10 + *s - '0',
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++s
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);
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return r;
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}
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