static VALUE
rb_ary_sample(int argc, VALUE *argv, VALUE ary)
{
VALUE nv, result;
VALUE opts, randgen = rb_cRandom;
long n, len, i, j, k, idx[10];
long rnds[numberof(idx)];
if (OPTHASH_GIVEN_P(opts)) {
VALUE rnd;
ID keyword_ids[1];
keyword_ids[0] = id_random;
rb_get_kwargs(opts, keyword_ids, 0, 1, &rnd);
if (rnd != Qundef) {
randgen = rnd;
}
}
len = RARRAY_LEN(ary);
if (argc == 0) {
if (len < 2)
i = 0;
else
i = RAND_UPTO(len);
return rb_ary_elt(ary, i);
}
rb_scan_args(argc, argv, "1", &nv);
n = NUM2LONG(nv);
if (n < 0) rb_raise(rb_eArgError, "negative sample number");
if (n > len) n = len;
if (n <= numberof(idx)) {
for (i = 0; i < n; ++i) {
rnds[i] = RAND_UPTO(len - i);
}
}
k = len;
len = RARRAY_LEN(ary);
if (len < k && n <= numberof(idx)) {
for (i = 0; i < n; ++i) {
if (rnds[i] >= len) return rb_ary_new_capa(0);
}
}
if (n > len) n = len;
switch (n) {
case 0:
return rb_ary_new_capa(0);
case 1:
i = rnds[0];
return rb_ary_new_from_values(1, &RARRAY_AREF(ary, i));
case 2:
i = rnds[0];
j = rnds[1];
if (j >= i) j++;
return rb_ary_new_from_args(2, RARRAY_AREF(ary, i), RARRAY_AREF(ary, j));
case 3:
i = rnds[0];
j = rnds[1];
k = rnds[2];
{
long l = j, g = i;
if (j >= i) l = i, g = ++j;
if (k >= l && (++k >= g)) ++k;
}
return rb_ary_new_from_args(3, RARRAY_AREF(ary, i), RARRAY_AREF(ary, j), RARRAY_AREF(ary, k));
}
if (n <= numberof(idx)) {
long sorted[numberof(idx)];
sorted[0] = idx[0] = rnds[0];
for (i=1; i<n; i++) {
k = rnds[i];
for (j = 0; j < i; ++j) {
if (k < sorted[j]) break;
++k;
}
memmove(&sorted[j+1], &sorted[j], sizeof(sorted[0])*(i-j));
sorted[j] = idx[i] = k;
}
result = rb_ary_new_capa(n);
RARRAY_PTR_USE(result, ptr_result, {
for (i=0; i<n; i++) {
ptr_result[i] = RARRAY_AREF(ary, idx[i]);
}
});
}
else {
result = rb_ary_dup(ary);
RBASIC_CLEAR_CLASS(result);
RB_GC_GUARD(ary);
RARRAY_PTR_USE(result, ptr_result, {
for (i=0; i<n; i++) {
j = RAND_UPTO(len-i) + i;
nv = ptr_result[j];
ptr_result[j] = ptr_result[i];
ptr_result[i] = nv;
}
});
RBASIC_SET_CLASS_RAW(result, rb_cArray);
}
ARY_SET_LEN(result, n);
return result;
}