.macro hex str
    .local char, value, byteValue, digitPlace
    digitPlace .set 0
    byteValue .set 0
    .repeat .strlen( str ), i
        char .set .strat( str, i )
        .if char <> '_' .and char <> '''
            .if char >= 'a' && char <= 'f'
                value .set char - 'a' + 10
            .elseif char >= 'A' && char <= 'F'
                value .set char - 'A' + 10
            .elseif char >= '0' && char <= '9'
                value .set char - '0'
            .else
                .fatal .sprintf( "hex: Invalid character '%c' encountered", char )
            .endif
            byteValue .set byteValue | ( value << ( 4 * ( 1 - digitPlace ) ) )
            digitPlace .set digitPlace ^ 1
            .if digitPlace = 0
                .byte byteValue
                byteValue .set 0
            .endif
        .endif
    .endrepeat
    .if digitPlace = 1
        .fatal .sprintf( "hex: Number of digits must be a multiple of two" )
    .endif
.endmacro

hex "112''''23_34_4f'f"
hex "09F9_1102_9D74E35BD84156C5635688C0"