Function: ash

ash is a function defined in data.c.

Signature

(ash VALUE COUNT)

Documentation

Return integer VALUE with its bits shifted left by COUNT bit positions.

If COUNT is negative, shift VALUE to the right instead. VALUE and COUNT must be integers. Mathematically, the return value is VALUE multiplied by 2 to the power of COUNT, rounded down. If the result is non-zero, its sign is the same as that of VALUE. In terms of bits, when COUNT is positive, the function moves the bits of VALUE to the left, adding zero bits on the right; when COUNT is negative, it moves the bits of VALUE to the right, discarding bits.

Other relevant functions are documented in the number group.

View in manual

Probably introduced at or before Emacs version 19.20.

Shortdoc

;; number
(ash 1 4)
    => 16
  (ash 16 -1)
    => 8

Source Code

// Defined in /usr/src/emacs/src/data.c
{
  CHECK_INTEGER (value);
  CHECK_INTEGER (count);

  if (! FIXNUMP (count))
    {
      if (BASE_EQ (value, make_fixnum (0)))
	return value;
      if (mpz_sgn (*xbignum_val (count)) < 0)
	{
	  EMACS_INT v = (FIXNUMP (value) ? XFIXNUM (value)
			 : mpz_sgn (*xbignum_val (value)));
	  return make_fixnum (v < 0 ? -1 : 0);
	}
      overflow_error ();
    }

  if (XFIXNUM (count) <= 0)
    {
      if (XFIXNUM (count) == 0)
	return value;

      if ((EMACS_INT) -1 >> 1 == -1 && FIXNUMP (value))
	{
	  EMACS_INT shift = -XFIXNUM (count);
	  EMACS_INT result
	    = (shift < EMACS_INT_WIDTH ? XFIXNUM (value) >> shift
	       : XFIXNUM (value) < 0 ? -1 : 0);
	  return make_fixnum (result);
	}
    }

  mpz_t const *zval = bignum_integer (&mpz[0], value);
  if (XFIXNUM (count) < 0)
    {
      if (TYPE_MAXIMUM (mp_bitcnt_t) < - XFIXNUM (count))
	return make_fixnum (mpz_sgn (*zval) < 0 ? -1 : 0);
      mpz_fdiv_q_2exp (mpz[0], *zval, - XFIXNUM (count));
    }
  else
    emacs_mpz_mul_2exp (mpz[0], *zval, XFIXNUM (count));
  return make_integer_mpz ();
}