I solved this problem in my previous company in Java. I will present the idea here but leave the implementation to you.

A IPv4 address is just a collection of four octets and can be represented by a 32 bit integer. Just convert the start and end address of the ip range to a 32 bit integer representation. Convert the Ipv4 address to be checked also into a 32 bit number and if the number falls between the start and end numbers, it is in the range. If the address check is called lots of times for a particular range, a integer comparison will be faster than a string comparison.

For example,
Start IP = 1.2.3.4 = 0x01020304 = 1057540 (decimal)
End IP = 12.6.255.255 = 0x0C06FFFF = 201785343 (decimal)
Target IP = 128.1.0.3 = 0x80010003 = 2147549187 (decimal)
2147549187 is not between 1057540 and 201785343 - so target ip is not in range.

Mahesh