PrimeNumbers.nim0

## Print `n` prime numbers greater than 3 and less than 399.
##
## Compile with `$ ./nim0 comp examples/PrimeNumbers`
## Try it with `$ ./nim0 run examples/PrimeNumbers`

proc PrimeNumbers* =
  var
    n, i, k, m, x, inc, lim, sqr: int
    prim: bool
    p: array[400, int]
    v: array[20, int]
  n = 399  # Number of primes to find

  # Initialize p[]
  i = 0
  while i <= n:
    p[i] = 0
    i = i + 1

  x = 1   # Prime candidate
  inc = 4 # Varying step to evaluate integers
  lim = 1
  sqr = 4 # Square root of ...
  m = 2   # Number of primes printed on the current line
  i = 3   # Number of prime to print

  # 1 and 3 are not found with this algorithmn
  write('1')
  write(' ')
  write('3')
  write(' ')

  while i <= n:
    x = x + inc
    inc = 6 - inc
    if sqr <= x:
      # sqr = p[lim]^2
      v[lim] = sqr
      lim = lim + 1
      sqr = p[lim] * p[lim]

    k = 2
    prim = true
    while prim and (k < lim):
      k = k + 1
      if v[k] < x:
        v[k] = v[k] + p[k]
      prim = x != v[k]
    while not prim:
      x = x + inc
      inc = 6 - inc
      if sqr <= x:
        # sqr = p[lim]^2
        v[lim] = sqr
        lim = lim + 1
        sqr = p[lim] * p[lim]

      k = 2
      prim = true
      while prim and (k < lim):
        k = k + 1
        if v[k] < x:
          v[k] = v[k] + p[k]
        prim = x != v[k]

    # Print 10 results per line
    p[i] = x
    write(x)
    write(' ')
    i = i + 1
    if m == 9:
      writeLine
      m = 0
    else:
      m = m + 1

  if m > 0:
    writeLine


# Let's go!
PrimeNumbers