From 081dace1c8497645018e89c77ef4afb79df2f295 Mon Sep 17 00:00:00 2001
From: IP2Location <support@ip2location.com>
Date: Tue, 14 Nov 2023 13:29:06 +0800
Subject: [PATCH] Fixed wrong value returned by CIDRToIPv6 function

---
 ip2location.go |  2 +-
 iptools.go     | 54 ++++++++++++++++++++++++++++++--------------------
 2 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/ip2location.go b/ip2location.go
index 4f4a6d5..62db7ec 100644
--- a/ip2location.go
+++ b/ip2location.go
@@ -159,7 +159,7 @@ var district_position = [27]uint8{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
 var asn_position = [27]uint8{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 24}
 var as_position = [27]uint8{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 25}
 
-const api_version string = "9.6.0"
+const api_version string = "9.6.1"
 
 var max_ipv4_range = uint128.From64(4294967295)
 var max_ipv6_range = uint128.From64(0)
diff --git a/iptools.go b/iptools.go
index 5b9786f..9808698 100644
--- a/iptools.go
+++ b/iptools.go
@@ -448,31 +448,43 @@ func (t *IPTools) CIDRToIPv6(CIDR string) ([]string, error) {
 		return nil, errors.New("Not a valid CIDR.")
 	}
 
-	hexstartaddress, _ := t.ExpandIPv6(ip)
-	hexstartaddress = strings.ReplaceAll(hexstartaddress, ":", "")
-	hexendaddress := hexstartaddress
-
-	bits := 128 - prefix
-	pos := 31
-
-	for bits > 0 {
-		values := []int{4, bits}
-		min, _ := t.minMax(values)
-		x, _ := strconv.ParseInt(string(hexendaddress[pos]), 16, 64)
-		y := fmt.Sprintf("%x", (x | int64(math.Pow(2, float64(min))-1)))
+	expand, _ := t.ExpandIPv6(ip)
+	parts := strings.Split(expand, ":")
+
+	bitStart := strings.Repeat("1", prefix) + strings.Repeat("0", 128-prefix)
+	bitEnd := strings.Repeat("0", prefix) + strings.Repeat("1", 128-prefix)
+
+	n := 16 // split string into 16-char parts
+	floors := []string{}
+	for i := 0; i < len(bitStart); i += n {
+		end := i + n
+		if end > len(bitStart) {
+			end = len(bitStart)
+		}
+		floors = append(floors, bitStart[i:end])
+	}
+	ceilings := []string{}
+	for i := 0; i < len(bitEnd); i += n {
+		end := i + n
+		if end > len(bitEnd) {
+			end = len(bitEnd)
+		}
+		ceilings = append(ceilings, bitEnd[i:end])
+	}
 
-		hexendaddress = hexendaddress[:pos] + y + hexendaddress[pos+1:]
+	start := []string{}
+	end := []string{}
 
-		bits = bits - 4
-		pos = pos - 1
+	for i := 0; i < 8; i += 1 {
+		p, _ := strconv.ParseUint(parts[i], 16, 64)
+		f, _ := strconv.ParseUint(floors[i], 2, 64)
+		c, _ := strconv.ParseUint(ceilings[i], 2, 64)
+		start = append(start, strconv.FormatUint(p&f, 16))
+		end = append(end, strconv.FormatUint(p|c, 16))
 	}
 
-	re2 := regexp.MustCompile(`(.{4})`)
-	hexstartaddress = re2.ReplaceAllString(hexstartaddress, "$1:")
-	hexstartaddress = strings.TrimSuffix(hexstartaddress, ":")
-	hexendaddress = re2.ReplaceAllString(hexendaddress, "$1:")
-	hexendaddress = strings.TrimSuffix(hexendaddress, ":")
-
+	hexstartaddress, _ := t.ExpandIPv6(strings.Join(start, ":"))
+	hexendaddress, _ := t.ExpandIPv6(strings.Join(end, ":"))
 	result := []string{hexstartaddress, hexendaddress}
 
 	return result, nil