dlvbug.go

//lint:file-ignore U1000 silence!

package main

import "fmt"

const (
	b6m = 63
	b4m = 15
)

type bts struct {
	b2 [16]byte
	b3 [2]uint64
}

var Bms *bts

func SetBms() {
	t := new(bts)
	t.b2 = [16]byte{0, 1}
	t.b3 = [2]uint64{0, uint64(1) << 2}
	Bms = t
	return
}

func main() {
	SetBms()
	/*Atest(0xe0d00101) // bad 1st
	Atest(0xe0e00102) // bad 2nd
	Atest(0xe0d00102) // ok  3rd
	Atest(0xe0d00202) // bad 4th
	*/
	b := []byte{
		0xe0, 0xd0, 0x01, 0x01,
		0xe0, 0xe0, 0x01, 0x02,
		0xe0, 0xd0, 0x01, 0x02,
		0xe0, 0xd0, 0x02, 0x02,
	}
	Filter(b, func(x u32, i int) { println("Aok:", x, " at", i) })
}

func Atest(a uint32) {
	// on this kind (short-circuited ors) debugger entered
	// in "true" block with all three parts being false (see pic)
	if a>>16 != 0xE0D0 ||
		Bms.b2[((a>>8)&b4m)] == 0 ||
		Bms.b3[Bms.b2[(a>>8)&b4m]]&(1<<(a&b6m)) == 0 {
		fmt.Printf("%08x !match by || short ciruit\n", a)
	}
	// on short-circuited ands debug worked ok
	if a>>16 == 0xE0D0 &&
		(Bms.b2[((a>>8)&b4m)] != 0) &&
		Bms.b3[Bms.b2[(a>>8)&b4m]]&(1<<(a&b6m)) != 0 {
		fmt.Printf("%08x  match by && short ciruit\n", a)
	}
}

type u32 = uint32

func Filter(buf []byte, aok func(x u32, i int)) {
	var a u32
	for i := 0; i < len(buf)-4; i += 4 {
		a = u32(buf[i+3]) | u32(buf[i+2])<<8 |
			u32(buf[i+1])<<16 | u32(buf[i])<<24
		if a>>16 != 0xE0D0 ||
			Bms.b2[((a>>8)&b4m)] == 0 ||
			Bms.b3[Bms.b2[(a>>8)&b4m]]&(1<<(a&b6m)) == 0 {
			continue
		}
		aok(a, i)
	}
}