# str.ludic — the string handling a compiler lives on: comparison, copying,
# slicing out substrings, and integer<->text. All over raw NUL-terminated
# byte buffers reached with peek8/poke8.

function char_is_digit(c: int) -> bool { return c >= '0' and c <= '9' }
function char_is_alpha(c: int) -> bool {
  if c >= 'A' and c <= 'Z' { return true }
  if c >= 'a' and c <= 'z' { return true }
  return c == '_'
}
function char_is_alnum(c: int) -> bool { return char_is_alpha(c) or char_is_digit(c) }

# does `s` begin with `prefix`? (byte-wise; both NUL-terminated)
function str_starts(s: pointer, prefix: pointer) -> bool {
  var i = 0
  while prefix[i] != 0 { if s[i] != prefix[i] { return false };  i += 1 }
  return true
}

# integer -> fresh decimal string
function itoa(v: int) -> pointer {
  if v == 0 { let z = bytes(2); z[0] = '0'; z[1] = 0; return z }
  # digits are taken off v as it is, never off -v: the most negative int has no positive twin, and
  # -v overflowed back to itself, so a 0x80000000 in an i32 was emitted as a bare "-"
  let neg = v < 0
  var x = v
  let tmp = bytes(24)
  var n = 0
  while x != 0 {
    var d = x % 10
    if d < 0 { d = -d }
    tmp[n] = 48 + d
    x /= 10
    n += 1
  }
  var total = n
  if neg { total += 1 }
  let out = bytes(total + 1)
  var k = 0
  if neg { out[0] = '-';  k = 1 }
  var i = 0
  while i < n { out[k + i] = tmp[n - 1 - i];  i += 1 }
  out[total] = 0
  return out
}