stdio: more compact scanf format parsing

src/stdio/scanf/scan.c

@@ -191,79 +191,52 @@ static int parse_fmt(char const *fmt, int *pos, struct scanf_format *opt)
 	int width = 0;
 	char size_letter = 0;
 
-	while(1) {
-		(*pos)++;
+	for((*pos)++;; (*pos)++) {
+		int c = fmt[*pos];
 
-		switch(fmt[*pos]) {
-		case '*':
+		if(c == '*')
 			opt->skip = true;
-			break;
+		else if(strchr("hlzjtL", c)) {
+			if(c == 'h')
+				opt->size = (size_letter=='h') ? sizeof(char) : sizeof(short);
+			else if(c == 'l')
+				opt->size = (size_letter=='l') ? sizeof(long long) :
+			                sizeof(long);
+			else if(c == 'z')
+				opt->size = sizeof(size_t);
+			else if(c == 'j')
+				opt->size = sizeof(intmax_t);
+			else if(c == 't')
+				opt->size = sizeof(ptrdiff_t);
+			else if(c == 'L')
+				opt->size = sizeof(long double);
 
-		case 'h':
-			opt->size = (size_letter=='h') ? sizeof(char) : sizeof(short);
-			size_letter = 'h';
-			break;
-		case 'l':
-			opt->size = (size_letter=='l') ? sizeof(long long) : sizeof(long);
-			size_letter = 'l';
-			break;
-		case 'L':
-			opt->size = sizeof(long double);
-			size_letter = 'L';
-			break;
-		case 'j':
-			opt->size = sizeof(intmax_t);
-			break;
-		case 'z':
-			opt->size = sizeof(size_t);
-			break;
-		case 't':
-			opt->size = sizeof(ptrdiff_t);
-			break;
-
-		case '0' ... '9':
+			size_letter = c;
+		}
+		else if(isdigit(c)) {
 			width = width * 10 + (fmt[*pos] - '0');
 			opt->field_width = width;
-			break;
-
-		case '[':
+		}
+		else if(c == '[') {
 			(*pos)++;
 			return bracket_set_parse(opt->bracket_set, fmt, pos) ? '[' : 0;
-
-		case 'd':
-		case 'i':
-		case 'o':
-		case 'u':
-		case 'x':
-		case 'X':
-		case 'p':
-		case 's':
-		case 'n':
-			return fmt[*pos];
-
-		case 'a':
-		case 'A':
-		case 'e':
-		case 'E':
-		case 'f':
-		case 'F':
-		case 'g':
-		case 'G':
+		}
+		else if(strchr("diouxXpsn", c))
+			return c;
+		else if(strchr("aAeEfFgG", c)) {
 			/* Adjust interpretation of no size / 'l' size  */
 			if(size_letter == 0)
 				opt->size = sizeof(float);
 			if(size_letter == 'l')
 				opt->size = sizeof(double);
-			return fmt[*pos];
-
-		case 'c':
+			return c;
+		}
+		else if(c == 'c') {
 			if(opt->field_width == INT_MAX)
 				opt->field_width = 1;
-			return 'c';
-
-		default:
-			return 0;
+			return c;
 		}
+		else return 0;
 	}
 	return 0;
 }
@@ -301,7 +274,6 @@ int __scanf(
 			return validrets;
 
 		switch(spec) {
-		// we need to decrypt the corresponding scanf set of character
 		case '[': {
 			int currentlength = 0;
 			// we need to assign the read char to the corresponding pointer
@@ -324,7 +296,6 @@ int __scanf(
 			break;
 		}
 
-		// return the number of char read so far (cannot be skipped %*n is not valid)
 		case 'n':
 			*va_arg(*args, int *) = in->bytes_read;
 			break;