add ip sub/half/middle functions

maker/golang/xdb/util.go

@@ -87,20 +87,59 @@ func IPSubOne(ip []byte) []byte {
 	return r
 }
 
-func IPMiddle(sip, eip []byte) []byte {
-	var result = make([]byte, len(sip))
-	var carry uint16 = 0
+// IPSub Sub the spcecified two byte ip
+func IPSub(sip, eip []byte) ([]byte, error) {
+	if len(sip) != len(eip) {
+		return []byte{}, fmt.Errorf("length of the two ips are not the same")
+	}
+
+	var carry uint16 = 0
+	var result = make([]byte, len(sip)+1)
 
-	// Add the two addresses with carry
 	for i := len(sip) - 1; i >= 0; i-- {
 		sum := uint16(sip[i]) + uint16(eip[i]) + carry
-		result[i] = byte(sum >> 0x01) // Divide by 2
-		carry = (sum & 0x01) << 7     // Carry for next byte (shift to MSB)
+		result[i+1] = byte(sum) // Store standard 8-bit result
+		carry = sum >> 8        // Extract the 1-bit carry for the next byte
+	}
+
+	// check and append the carry
+	if carry > 0 {
+		result[0] = byte(carry)
+		return result, nil
+	} else {
+		return result[1:], nil
+	}
+}
+
+// IPHalf get the half value of an input byte ip
+func IPHalf(ip []byte) []byte {
+	var length = len(ip)
+	var result = make([]byte, length)
+	// Tracks the bit falling off from the previous byte
+	var carry byte = 0
+
+	for i := 0; i < length; i++ {
+		// 1. Shift current byte right by 1
+		// 2. Or (|) with the carry from the previous byte (shifted to the MSB position)
+		result[i] = (ip[i] >> 1) | (carry << 7)
+
+		// 3. Capture the Least Significant Bit (LSB) to use as carry for the next byte
+		carry = ip[i] & 1
 	}
 
 	return result
 }
 
+// IPMiddle get the middle value of two input ip address
+func IPMiddle(sip, eip []byte) ([]byte, error) {
+	buf, err := IPSub(sip, eip)
+	if err != nil {
+		return []byte{}, fmt.Errorf("IPSub(%s, %s): %w", IP2String(sip), IP2String(eip), err)
+	}
+
+	return IPHalf(buf), nil
+}
+
 func IterateSegments(handle *os.File, before func(l string), filter func(region string) (string, error), done func(seg *Segment) error) error {
 	var last *Segment = nil
 	var scanner = bufio.NewScanner(handle)

maker/golang/xdb/util_test.go

@@ -5,6 +5,7 @@
 package xdb
 
 import (
+	"encoding/binary"
 	"fmt"
 	"os"
 	"testing"
@@ -99,6 +100,102 @@ func TestIPSubOne2(t *testing.T) {
 	fmt.Printf("nip: %+v, ip:%+v", ip, nip)
 }
 
+func TestIPSub(t *testing.T) {
+	var strToSub = "1.2.3.4"
+	bytesToSub, err := ParseIP(strToSub)
+	if err != nil {
+		t.Fatalf("failed to parse ip %s", strToSub)
+	}
+	var intToSub = int(binary.BigEndian.Uint32(bytesToSub))
+	t.Logf("to sub ip: %d -> %s", intToSub, strToSub)
+
+	counter := 0
+	buf := make([]byte, 4)
+	for i := 0; i < 0x2FFFFFFF; i++ {
+		binary.BigEndian.PutUint32(buf, uint32(i))
+		subVal, err := IPSub(buf, bytesToSub)
+		if err != nil {
+			t.Fatalf("failed to IPSub(%s,%s): %s", IP2String(buf), strToSub, err)
+		}
+
+		// do it as two integers
+		byteSub := int(binary.BigEndian.Uint32(subVal))
+		intSub := i + intToSub
+		if byteSub != intSub {
+			t.Fatal("byte and int sub value are not the same")
+		}
+
+		counter++
+	}
+
+	t.Logf("test done with %d ips", counter)
+}
+
+func TestIPHalf(t *testing.T) {
+	var buf = make([]byte, 4)
+	for i := 0; i < 0xFFFFFFFF; i++ {
+		binary.BigEndian.PutUint32(buf, uint32(i))
+		half := IPHalf(buf)
+
+		// do it as two integers
+		byteMiddle := binary.BigEndian.Uint32(half)
+		intMidle := i >> 1
+		if byteMiddle != uint32(intMidle) {
+			t.Fatal("byte middle and int middle are not the same")
+		}
+	}
+}
+
+func TestSubOverflow(t *testing.T) {
+	var ip1Str = "255.255.255.250"
+	ip1Bytes, err := ParseIP(ip1Str)
+	if err != nil {
+		t.Fatalf("failed to ParseIP(%s): %s", ip1Str, err)
+	}
+
+	var buff = make([]byte, 4)
+	for i := 0; i < 10; i++ {
+		binary.BigEndian.PutUint32(buff, uint32(i))
+		ipSub, err := IPSub(ip1Bytes, buff)
+		if err != nil {
+			t.Fatalf("failed to IPSub(%s, %s): %s", ip1Str, IP2String(buff), err)
+		}
+
+		t.Logf("IPSub(%s, %s) = %+v", ip1Str, IP2String(buff), ipSub)
+	}
+}
+
+func TestIPMiddle(t *testing.T) {
+	var sIPStr = "0.0.0.0"
+	sBytes, err := ParseIP(sIPStr)
+	if err != nil {
+		t.Fatalf("failed to parse ip %s", sIPStr)
+	}
+	var sInt = int(binary.BigEndian.Uint32(sBytes))
+	t.Logf("start ip: %d -> %s", sInt, sIPStr)
+
+	counter := 0
+	buf := make([]byte, 4)
+	for i := 0; i < 0x0FFFFFFF; i++ {
+		binary.BigEndian.PutUint32(buf, uint32(i))
+		midVal, err := IPMiddle(sBytes, buf)
+		if err != nil {
+			t.Fatalf("failed to IPMiddle(%s,%s): %s", sIPStr, IP2String(buf), err)
+		}
+
+		// do it as two integers
+		byteMid := int(binary.BigEndian.Uint32(midVal))
+		intMid := (sInt + i) >> 1
+		if byteMid != intMid {
+			t.Fatal("byte and int middle value are not the same")
+		}
+
+		counter++
+	}
+
+	t.Logf("test done with %d ips", counter)
+}
+
 func TestSplitSegmentV4(t *testing.T) {
 	// var str = "1.1.0.0|1.3.3.24|中国|广东|深圳|电信"
 	// var str = "0.0.0.0|1.255.225.254|0|0|0|内网IP|内网IP"