mod_big_number.awk

#awk '
function chunk_mod(s) {
    len = 6 # 6 digits in case of 32-bit awk version
    result = 0
    while (length(s) > 0) {
        chunk = substr(s, 1, len)
        s = substr(s, len + 1)
        result = (result * (10 ^ length(chunk)) + chunk) % 97
    }
    return result
}


function assert_expected(actual, expected, message) {
    if (BLOCK_ASSERTIONS) {
        return
    }
    if (!length(message)) {
        message = "An assertion failed."
    }
    if (actual != expected) {
        printf "%s (expected: \"%s\", got \"%s\")\n", message, expected, actual > "/dev/stderr"
        close("/dev/stderr")
        exit 1
    }
}


BEGIN {
  PREC = "octal"

  assert_expected(chunk_mod("12345678"), 3, "chunk_mod(\"12345678\")")
  assert_expected(chunk_mod("12345678901234567890123456789012345678901234567890123456789012345678901234567890"),54, "chunk_mod(\"12345678901234567890123456789012345678901234567890123456789012345678901234567890\")")
  assert_expected(chunk_mod("12345678901230"),84, "chunk_mod(\"12345678901230\")")
  assert_expected(chunk_mod("200410000159081552302045152700"), 77, "chunk_mod(\"200410000159081552302045152700\")")

  print 200410000159081552302045152700 % 97
  print "All tests passed."
}
#'