millfork/include/c64_basic.mfk

// Routines from C64 BASIC ROM

import c64_kernal

// print a 16-bit number on the standard output
asm void putword(word xa) @$BDCD extern
asm void readline() @$A560 extern
const pointer readline_out = $200

byte readword_err

word readword() {
    readline()
    readword_err = 0
    word result
    word four
    result = 0
    byte char
    byte i
    i = 0
    while true {
        char = readline_out[i]
        if char == 0 {
            if i == 0 {
                readword_err = 1
            }
            return result
        }
        if 48 <= char <= 48+9 {
            four = result
            four <<= 2
            result += four
            result <<= 1
            result += char - 48
        } else {
            readword_err = 1
            return result
        }
        i += 1
    }
}