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Filename : 02_bounds_checking.re

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//go:generate re2go $INPUT -o $OUTPUT
package main

import (
	"strings"
	"testing"
)

/*!max:re2c*/

// Expects YYMAXFILL-padded string.
func lex(str string) int {
	var cursor int
	limit := len(str)
	count := 0
loop:
	/*!re2c
	re2c:define:YYCTYPE    = byte;
	re2c:define:YYPEEK     = "str[cursor]";
	re2c:define:YYSKIP     = "cursor += 1";
	re2c:define:YYLESSTHAN = "limit - cursor < @@{len}";
	re2c:define:YYFILL     = "return -1";

	* {
		return -1
	}
	[\x00] {
		if limit - cursor == YYMAXFILL - 1 {
			return count
		} else {
			return -1
		}
	}
	['] ([^'\\] | [\\][^])* ['] {
		count += 1;
		goto loop
	}
	[ ]+ {
		goto loop
	}
	*/
}

// Pad string with YYMAXFILL zeroes at the end.
func pad(str string) string {
	return str + strings.Repeat("\000", YYMAXFILL)
}

func TestLex(t *testing.T) {
	var tests = []struct {
		res int
		str string
	}{
		{0, ""},
		{3, "'qu\000tes' 'are' 'fine: \\'' "},
		{-1, "'unterminated\\'"},
	}

	for _, x := range tests {
		t.Run(x.str, func(t *testing.T) {
			res := lex(pad(x.str))
			if res != x.res {
				t.Errorf("got %d, want %d", res, x.res)
			}
		})
	}
}