Add original unix v6

source/s4/atoi.c

@@ -0,0 +1,24 @@
+atoi(ap)
+char *ap;
+{
+	register n, c;
+	register char *p;
+	int f;
+
+	p = ap;
+	n = 0;
+	f = 0;
+loop:
+	while(*p == ' ' || *p == '	')
+		p++;
+	if(*p == '-') {
+		f++;
+		p++;
+		goto loop;
+	}
+	while(*p >= '0' && *p <= '9')
+		n = n*10 + *p++ - '0';
+	if(f)
+		n = -n;
+	return(n);
+}