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Filename : parse_u32_conditions.re
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//go:generate re2go -c $INPUT -o $OUTPUT -i
package main

import (
	"errors"
	"testing"
)

var (
	eSyntax   = errors.New("syntax error")
	eOverflow = errors.New("overflow error")
)

/*!types:re2c*/

const u32Limit uint64 = 1<<32

func parse_u32(str string) (uint32, error) {
	var cursor, marker int
	result := uint64(0)
	cond := yycinit

	add_digit := func(base uint64, offset byte) {
		result = result * base + uint64(str[cursor-1] - offset)
		if result >= u32Limit {
			result = u32Limit
		}
	}

	/*!re2c
	re2c:yyfill:enable = 0;
	re2c:define:YYCTYPE        = byte;
	re2c:define:YYPEEK         = "str[cursor]";
	re2c:define:YYSKIP         = "cursor += 1";
	re2c:define:YYSHIFT        = "cursor += @@{shift}";
	re2c:define:YYBACKUP       = "marker = cursor";
	re2c:define:YYRESTORE      = "cursor = marker";
	re2c:define:YYGETCONDITION = "cond";
	re2c:define:YYSETCONDITION = "cond = @@";

	<*> * { return 0, eSyntax }

	<init> '0b' / [01]        :=> bin
	<init> "0"                :=> oct
	<init> ""   / [1-9]       :=> dec
	<init> '0x' / [0-9a-fA-F] :=> hex

	<bin, oct, dec, hex> "\x00" {
		if result < u32Limit {
			return uint32(result), nil
		} else {
			return 0, eOverflow
		}
	}

	<bin> [01]  { add_digit(2, '0');     goto yyc_bin }
	<oct> [0-7] { add_digit(8, '0');     goto yyc_oct }
	<dec> [0-9] { add_digit(10, '0');    goto yyc_dec }
	<hex> [0-9] { add_digit(16, '0');    goto yyc_hex }
	<hex> [a-f] { add_digit(16, 'a'-10); goto yyc_hex }
	<hex> [A-F] { add_digit(16, 'A'-10); goto yyc_hex }
	*/
}

func TestLex(t *testing.T) {
	var tests = []struct {
		num uint32
		str string
		err error
	}{
		{1234567890, "1234567890\000", nil},
		{13, "0b1101\000", nil},
		{0x7fe, "0x007Fe\000", nil},
		{0644, "0644\000", nil},
		{0, "9999999999\000", eOverflow},
		{0, "123??\000", eSyntax},
	}

	for _, x := range tests {
		t.Run(x.str, func(t *testing.T) {
			num, err := parse_u32(x.str)
			if !(num == x.num && err == x.err) {
				t.Errorf("got %d, want %d", num, x.num)
			}
		})
	}
}