64-bit integer support in 6502 assembly language for Commodore 64

Methods implemented

• int64_zero - initialize with zero
• int64_arg1 - set first argument value
• int64_adc - 64-bit addition (with carry)
• int64_sbc - 64-bit subtraction (with carry)
• int64_compare - compare 64-bit numbers (sets Z, C)
• int64_negate - toggle negative/positive 64-bit number
• int64_mul - 64-bit multication result is 128-bit
• int128_div - 128-bit number divided by 64-bit, 128-bit result and remainder
• int64_tostring - convert int64 value to string (decimal, binary, octal, or hex)
• int128_tostring - convert int128 value to string (decimal, binary, octal, or hex)

Methods yet to be implemented

• int64_fromstring

Limitations

• build script requires Bash shell or equivalent (to do: add a batch file)
• division ignoring signed values, assuming unsigned for now (note: work in progress)
• tostring methods missing support for negative values
• 128-bit support is unsymmetrical, especially division
• recommend add full 8-bit/16-bit/32-bit/64-bit/128-bit support with mix
• adding macros for iterative low level operations could simplify code
• compare ignoring signed values, assuming unsigned for now
• missing implementation for initializing from string (decimal, hex, binary)
• flags may not be correct for overflow, negative, etc.
• doesn't unroll loops, not focused on maximum speed performance
• tostring methods are slow based on repetitive division of 128bits by 128bits, could be optimized