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struct sample_with_memo_arg {

VALUE randgen, ary;

long len, n;

st_table *memo;

VALUE result;

};

static VALUE

sample_with_memo(VALUE a)

{

struct sample_with_memo_arg *arg = (void *)a;

VALUE randgen = arg->randgen;

long i, j, i2, j2, len;

st_data_t value;

RARRAY_PTR_USE(arg->result, ptr_result, {

for (i=0; i<arg->n; i++) {

ptr_result[i] = RAND_UPTO(arg->len-i) + i;

}

len = RARRAY_LEN(arg->ary);

if (len < arg->len) {

for (i=0; i<arg->n; i++) {

if ((long)ptr_result[i] >= len) arg->n = 0;

}

if (arg->n > len) arg->n = len;

}

for (i=0; i<arg->n; i++) {

j2 = j = ptr_result[i];

i2 = i;

if (st_lookup(arg->memo, (st_data_t)i, &value)) i2 = (long)value;

if (st_lookup(arg->memo, (st_data_t)j, &value)) j2 = (long)value;

st_insert(arg->memo, (st_data_t)j, (st_data_t)i2);

ptr_result[i] = rb_ary_elt(arg->ary, j2);

}

});

return Qnil;

}

static VALUE

ensure_sample_with_memo(VALUE arg)

{

st_free_table((st_table*)arg);

return Qnil;

}

else if (n <= (len<2560 ? len/128 : len<5120 ? len/64 : len<10240 ? len/32 : len/16)) {

struct sample_with_memo_arg arg = { randgen, ary, len, n };

arg.memo = st_init_numtable_with_size(n);

result = arg.result = rb_ary_new_capa(n);

rb_ensure(sample_with_memo, (VALUE)&arg, ensure_sample_with_memo, (VALUE)arg.memo);

n = arg.n;

}