make echo better

lib/libio.c

@@ -1,7 +1,24 @@
 #include <ctype.h>
+#include <string.h>
 #include <unistd.h>
 #include "libio.h"
 
+/* Backups of standard library systems for the odd scenario where there is no
+ * standard library but there is the write(2) system call. */
+static int _isdigit(int c);
+static int _strlen(char *s);
+
+/* Wrappers around write(2) */
+static int _write(int fd, char *s, int n);
+static int _write1(int fd, int c);
+
+/* Normally in <ctype.h> */
+static int
+_isdigit(int c){
+	return c >= '0' && c <= '9';
+}
+
+/* Normally in <string.h> */
 static int
 _strlen(char *s){
 	int i;
@@ -11,6 +28,8 @@ _strlen(char *s){
 	return i;
 }
 
+/* Wrapper around write(2) - keeps re-running write(2) until the operation
+ * succeeds in full. Usually unnecessary but still good. */
 static int
 _write(int fd, char *s, int n){
 	int i;
@@ -24,32 +43,40 @@ _write(int fd, char *s, int n){
 	return i;
 }
 
-int
-fdprint(int fd, char *s){
-	return _write(fd, s, _strlen(s));
-}
-
-/* SLOW. DO NOT USE. */
-static int write1(int fd, int c){
+/* For writing a single character. To optimize for speed, functions should
+ * allocate a buffer and add to that buffer before write(2)ing the buffer out
+ * in a single system call. However sometimes cheap tricks are as effective. */
+static int
+_write1(int fd, int c){
 	while(write(fd, &c, 1) != 1);
 	return 1;
 }
 
-int fdputd(int fd, int d){
+int
+fdprint(int fd, char *s){
+	return _write(fd, s, strlen(s));
+}
+
+int
+fdputd(int fd, int d){
 	int r;
 	int s;
 
 	r = 0;
 	/* Just an implementation looking for a math person to improve it... */
+	/* Rather than storing the log base 10 of d, store 10^(log base 10 (d))
+	 * which requires less Weird Hax. Then slowly chop off digits and print
+	 * out the system encoding's representations. Finally, print a newline.
+	 * Generally this function is slow and sucks implementation-wise. */
 	if(d < 100){
 		s = d < 10 ? 1 : 10;
 		goto put;
 	}
 	for(s = 10; d > (s *= 10););
 put:	while(s > 0){
-		r += write1(1, (d - (d % s)) / s + '0');
+		r += _write1(fd, (d - (d % s)) / s + '0');
 		if((s /= 10) == 0)
-			r += write1(1, '\n');
+			r += _write1(fd, '\n');
 	}
 
 	return r;
@@ -60,7 +87,7 @@ fdputs(int fd, char *s){
 	int i;
 	int r;
 
-	i = _strlen(s);
+	i = strlen(s);
 
 	/* RACE CONDITION */
 	/* This leaves s as an invalid string while the write(2) syscall is

src/echo.c

@@ -1,16 +1,15 @@
 #include <sysexits.h>
 #include <stddef.h> /* NULL */
 #include <unistd.h> /* write(2) */
+#include "libio.h" /* fdprint(3) */
 
 int main(int argc, char **argv){
-	int s;
 
 	if(*argv == NULL)
 		return EX_OSERR;
 	
 	while(*++argv != NULL){
-		for(s = 0; *(*argv+s) != '\0'; ++s);
-		write(1, *argv, s);
+		fdprint(1, *argv);
 
 		if(*(argv+1) != NULL)
 			write(1, " ", 1);