import Foundation
let pattern = #"0x(([[:xdigit:]]{7}\b)|([[:xdigit:]]{6}\b)|([[:xdigit:]]{5}\b)|([[:xdigit:]]{4}\b)|([[:xdigit:]]{3}\b)|([[:xdigit:]]{2}\b)|([[:xdigit:]]{1}\b))"#
let regex = try! NSRegularExpression(pattern: pattern, options: .anchorsMatchLines)
let testString = #"""
{0x1023350, 0x3014},
{0x1023954, 0x3007},
{0x1023960, 0x10F},
{0x102396C, 0x2FF},
{0x10219, 0x16},
"""#
let stringRange = NSRange(location: 0, length: testString.utf16.count)
let substitutionString = #"0x(?{2}0)(?{3}00)(?{4}000)(?{5}0000)(?{6}00000)(?{7}000000)(?{8}0000000)${1}"#
let result = regex.stringByReplacingMatches(in: testString, range: stringRange, withTemplate: substitutionString)
print(result)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Swift 5.2, please visit: https://developer.apple.com/documentation/foundation/nsregularexpression