prime_sieve.wat en WebAssembly

La criba de Eratóstenes en memoria lineal: 25 primos hasta 100.

;; Sieve of Eratosthenes in one memory page: count the primes to 100.
(module
  (memory 1)

  ;; Mark every composite: for each prime p, cross off p*p, p*p+p, ...
  (func $sieve (param $limit i32)
    (local $p i32)
    (local $m i32)
    (local.set $p (i32.const 2))
    (block $done
      (loop $next_p
        (br_if $done
          (i32.gt_s (i32.mul (local.get $p) (local.get $p))
                    (local.get $limit)))
        (if (i32.eqz (i32.load8_u (local.get $p)))
          (then
            (local.set $m (i32.mul (local.get $p) (local.get $p)))
            (block $marked
              (loop $mark
                (br_if $marked
                  (i32.gt_s (local.get $m) (local.get $limit)))
                (i32.store8 (local.get $m) (i32.const 1))
                (local.set $m (i32.add (local.get $m) (local.get $p)))
                (br $mark)))))
        (local.set $p (i32.add (local.get $p) (i32.const 1)))
        (br $next_p))))

  ;; Anything still zero after the sieve is prime.
  (func $count_primes (export "count_primes") (param $limit i32)
        (result i32)
    (local $n i32)
    (local $count i32)
    (call $sieve (local.get $limit))
    (local.set $n (i32.const 2))
    (block $done
      (loop $scan
        (br_if $done (i32.gt_s (local.get $n) (local.get $limit)))
        (if (i32.eqz (i32.load8_u (local.get $n)))
          (then
            (local.set $count
              (i32.add (local.get $count) (i32.const 1)))))
        (local.set $n (i32.add (local.get $n) (i32.const 1)))
        (br $scan)))
    (local.get $count))

  ;; There are 25 primes at or below 100.
  (func (export "main") (result i32)
    (call $count_primes (i32.const 100))))

Cómo funciona

1. $sieve tacha compuestos, cada primo avanzando desde p*p.
2. Pares block/loop anidados arman el for de dos niveles.
3. count_primes reescanea la memoria; main responde 25 para 100.

Palabras clave y builtins usados aquí

• block
• br
• br_if
• call
• export
• func
• i32
• if
• local
• loop
• memory
• module
• param
• result
• then

El intento, en números

Líneas

48

Caracteres a escribir

1355

Tokens

314

Ritmo de tres estrellas

60 tpm

Al ritmo de tres estrellas de 60 tokens por minuto, este intento toma unos 314 segundos.

Escribe este fragmento

Paso 1 de 3 en Bis; paso 26 de 28 en Fundamentos del lenguaje.

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