TM4C123 has 256 kiBytes of flash ROM as shown in the memory map. The range of memory addresses for the ROM is 0x0000.0000 to 0x0003.FFFF (a 32bit address), totaled to 3x16x16x16x16 = 196,608 number of addresses. The memory is byte addressable so that block of memory addresses adds up to 196,608 bytes instead. Why does the manufacturer claim it has 256 kiB and not 196kB ROM memory size?
Even if the range of addresses can't sum up to an exact 256k, wouldn't 0x0000.0000 - 0.0004.FFFF (4x16x16x16x16 = 262k) give a size closer to 256k than 0x0003.FFFF's 196k?