method

rand

v1_9_1_378 - Show latest stable - Class: Kernel

rand(p1 = v1)

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]

static VALUE
rb_f_rand(int argc, VALUE *argv, VALUE obj)
{
    VALUE vmax;
    long val, max;
    struct MT *mt = &default_mt.mt;

    rb_scan_args(argc, argv, "01", &vmax);
    if (!genrand_initialized(mt)) {
        rand_init(mt, random_seed());
    }
    switch (TYPE(vmax)) {
      case T_FLOAT:
        if (RFLOAT_VALUE(vmax) <= LONG_MAX && RFLOAT_VALUE(vmax) >= LONG_MIN) {
            max = (long)RFLOAT_VALUE(vmax);
            break;
        }
        if (RFLOAT_VALUE(vmax) < 0)
            vmax = rb_dbl2big(-RFLOAT_VALUE(vmax));
        else
            vmax = rb_dbl2big(RFLOAT_VALUE(vmax));
        /* fall through */
      case T_BIGNUM:
      bignum:
        {
            struct RBignum *limit = (struct RBignum *)vmax;
            if (!RBIGNUM_SIGN(limit)) {
                limit = (struct RBignum *)rb_big_clone(vmax);
                RBIGNUM_SET_SIGN(limit, 1);
            }
            limit = (struct RBignum *)rb_big_minus((VALUE)limit, INT2FIX(1));
            if (FIXNUM_P((VALUE)limit)) {
                if (FIX2LONG((VALUE)limit) == -1)
                    return DBL2NUM(genrand_real(mt));
                return LONG2NUM(limited_rand(mt, FIX2LONG((VALUE)limit)));
            }
            return limited_big_rand(mt, limit);
        }
      case T_NIL:
        max = 0;
        break;
      default:
        vmax = rb_Integer(vmax);
        if (TYPE(vmax) == T_BIGNUM) goto bignum;
      case T_FIXNUM:
        max = FIX2LONG(vmax);
        break;
    }

    if (max == 0) {
        return DBL2NUM(genrand_real(mt));
    }
    if (max < 0) max = -max;
    val = limited_rand(mt, max-1);
    return LONG2NUM(val);
}

rand

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