Author: Ricardo Gibert
Date: 07:54:29 07/14/03
Go up one level in this thread
On July 14, 2003 at 03:19:37, Matthew White wrote:
>On July 14, 2003 at 02:00:39, Ricardo Gibert wrote:
>
>>On July 14, 2003 at 00:56:12, Matthew White wrote:
>>
>>>Hi all,
>>>
>>>I was browsing through the code in KnightCap, and I noticed the following
>>>function. Doesn't this seem like an incorrect definition of a pinned piece? I
>>>thought that a pinned piece was when a lower valued piece was blocking the
>>>attack on a higher valued piece (or the king). Any ideas?
>>
>>White: Re1
>>Black: Be6, Pe7, Pf7
>>
>>The B is pinned, since if it is moved, the pawn on e7 drops. Note the B is of
>>greater value than the P.
>>
>>If we remove the Pf7, then we have a skewer instead. The B must move and give up
>>the P.
>>
>Would a hanging pieces function pick that up more effectively?
I'm not sure what you mean. In any case, I'm probably not the right person to
ask this question.
>>>
>>>Matt
>>>
>>>static etype find_pins(Position *b)
>>>{
>>> int i, j, k;
>>> uint32 pinner_mask;
>>>
>>> /* to find pins we loop over all pieces, looking for pieces
>>> that are under attack by sliding pieces (but not if they
>>> themselves are sliding pieces of the same type!). Then we
>>> check to see if the sliding piece would attack another
>>> piece, making it hung, if moved.
>>>
>>> This is a expensive procedure! */
>>>
>>> b->pinned_mask = 0;
>>>
>>> if (b->stage == MATING)
>>> return 0;
>>>
>>> for (i=2;i<16;i++) {
>>> if (!b->pieces[i].p) continue;
>>>
>>> pinner_mask = b->topieces[b->pieces[i].pos] &
>>> b->sliding_mask & BLACK_MASK;
>>>
>>> while (pinner_mask) {
>>> j = ff_one(pinner_mask);
>>> pinner_mask &= ~(1<<j);
>>>
>>> /* If the pinned piece is attacking the pinner then
>>> it isn't a pin! It might be a skewer tho.
>>> */
>>> if (b->topieces[b->pieces[j].pos] & (1<<i))
>>> continue;
>>>
>>> /* look for a piece that this bit is pinned against */
>>> for (k=0;k<8;k++) {
>>> if (!b->pieces[k].p) continue;
>>> if (k == i) continue;
>>> if (!same_line(b->pieces[j].pos, b->pieces[i].pos,
>>> b->pieces[k].pos)) continue;
>>> if (!empty_line(b, b->pieces[i].pos,
>>> b->pieces[k].pos))
>>> continue;
>>>
>>> /* we have a likely pin. Now we need
>>> to confirm that if the pinner could attack
>>> the pinnedto piece then that piece
>>> would be hung */
>>> if (get_control(b,
>>> b->topieces[b->pieces[k].pos] | (1<<j),
>>> b->pieces[k].p,
>>> b->pieces[k].pos) < 0) {
>>> b->pinned_mask |= (1<<i);
>>> if (debug)
>>> lprintf(0,"w pinned %s -> %s -> %s\n",
>>> posstr(b->pieces[j].pos),
>>> posstr(b->pieces[i].pos),
>>> posstr(b->pieces[k].pos)
>>> );
>>> }
>>> }
>>> }
>>> }
>>>
>>>
>>> for (i=18;i<32;i++) {
>>> if (!b->pieces[i].p) continue;
>>>
>>> pinner_mask = b->topieces[b->pieces[i].pos] &
>>> b->sliding_mask & WHITE_MASK;
>>>
>>> while (pinner_mask) {
>>> j = ff_one(pinner_mask);
>>> pinner_mask &= ~(1<<j);
>>>
>>> /* If the pinned piece is attacking the pinner then
>>> it isn't a pin! It might be a skewer tho.
>>> */
>>> if (b->topieces[b->pieces[j].pos] & (1<<i))
>>> continue;
>>>
>>> /* look for a piece that this bit is pinned against */
>>> for (k=16;k<24;k++) {
>>> if (!b->pieces[k].p) continue;
>>> if (k == i) continue;
>>> if (!same_line(b->pieces[j].pos, b->pieces[i].pos,
>>> b->pieces[k].pos)) continue;
>>> if (!empty_line(b, b->pieces[i].pos,
>>> b->pieces[k].pos))
>>> continue;
>>>
>>> /* we have a likely pin. Now we need
>>> to confirm that if the pinner could attack
>>> the pinnedto piece then that piece
>>> would be hung */
>>> if (get_control(b,
>>> b->topieces[b->pieces[k].pos] | (1<<j),
>>> b->pieces[k].p,
>>> b->pieces[k].pos) > 0) {
>>> b->pinned_mask |= (1<<i);
>>> if (debug)
>>> lprintf(0,"b pinned %s -> %s -> %s\n",
>>> posstr(b->pieces[j].pos),
>>> posstr(b->pieces[i].pos),
>>> posstr(b->pieces[k].pos)
>>> );
>>> }
>>> }
>>> }
>>> }
>>>
>>> return 0;
>>>}
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