method

rand

v1_8_6_287 - Show latest stable - 0 notes - Class: Kernel

rand(...) public

Converts max to an integer using max1 = max.to_i.abs. If the result is zero, returns a pseudorandom floating point number greater than or equal to 0.0 and less than 1.0. Otherwise, returns a pseudorandom integer greater than or equal to zero and less than max1. Kernel::srand may be used to ensure repeatable sequences of random numbers between different runs of the program. Ruby currently uses a modified Mersenne Twister with a period of 2**19937-1.

   srand 1234                 #=> 0
   [ rand,  rand ]            #=> [0.191519450163469, 0.49766366626136]
   [ rand(10), rand(1000) ]   #=> [6, 817]
   srand 1234                 #=> 1234
   [ rand,  rand ]            #=> [0.191519450163469, 0.49766366626136]

Show source

/*
 *  call-seq:
 *     rand(max=0)    => number
 *  
 *  Converts <i>max</i> to an integer using max1 =
 *  max<code>.to_i.abs</code>. If the result is zero, returns a
 *  pseudorandom floating point number greater than or equal to 0.0 and
 *  less than 1.0. Otherwise, returns a pseudorandom integer greater
 *  than or equal to zero and less than max1. <code>Kernel::srand</code>
 *  may be used to ensure repeatable sequences of random numbers between
 *  different runs of the program. Ruby currently uses a modified
 *  Mersenne Twister with a period of 2**19937-1.
 *     
 *     srand 1234                 #=> 0
 *     [ rand,  rand ]            #=> [0.191519450163469, 0.49766366626136]
 *     [ rand(10), rand(1000) ]   #=> [6, 817]
 *     srand 1234                 #=> 1234
 *     [ rand,  rand ]            #=> [0.191519450163469, 0.49766366626136]
 */

static VALUE
rb_f_rand(argc, argv, obj)
    int argc;
    VALUE *argv;
    VALUE obj;
{
    VALUE vmax;
    long val, max;

    rb_scan_args(argc, argv, "01", &vmax);
    if (first) {
        rand_init(random_seed());
    }
    switch (TYPE(vmax)) {
      case T_FLOAT:
        if (RFLOAT(vmax)->value <= LONG_MAX && RFLOAT(vmax)->value >= LONG_MIN) {
            max = (long)RFLOAT(vmax)->value;
            break;
        }
        if (RFLOAT(vmax)->value < 0)
            vmax = rb_dbl2big(-RFLOAT(vmax)->value);
        else
            vmax = rb_dbl2big(RFLOAT(vmax)->value);
        /* fall through */
      case T_BIGNUM:
      bignum:
        {
            struct RBignum *limit = (struct RBignum *)vmax;
            if (!limit->sign) {
                limit = (struct RBignum *)rb_big_clone(vmax);
                limit->sign = 1;
            }
            limit = (struct RBignum *)rb_big_minus((VALUE)limit, INT2FIX(1));
            if (FIXNUM_P((VALUE)limit)) {
                if (FIX2LONG((VALUE)limit) == -1)
                    return rb_float_new(genrand_real());
                return LONG2NUM(limited_rand(FIX2LONG((VALUE)limit)));
            }
            return limited_big_rand(limit);
        }
      case T_NIL:
        max = 0;
        break;
      default:
        vmax = rb_Integer(vmax);
        if (TYPE(vmax) == T_BIGNUM) goto bignum;
        /* fall through */
      case T_FIXNUM:
        max = FIX2LONG(vmax);
        break;
    }

    if (max == 0) {
        return rb_float_new(genrand_real());
    }
    if (max < 0) max = -max;
    val = limited_rand(max-1);
    return LONG2NUM(val);
}

rand

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