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products/sources/formale Sprachen/GAP/pkg/nq/src/ (Algebra von RWTH Aachen Version 4.15.1^©) Datei vom 12.0.2024 mit Größe 7 kB

Quelle combicol.c Sprache: C

/*****************************************************************************
**
**    combicol.c                      NQ                       Werner Nickel
**                                         nickel@mathematik.tu-darmstadt.de
*/

#include "config.h"

#include "mem.h"
#include "pc.h"
#include "pcarith.h"
#include "macro.h"
#include "collect.h"
#include "time.h"
#include "system.h"

static int Error(const char *str, gen g) {
printf("Error in CombiCollect() while treating generator %d:\n",
        (int)g);
printf(" %s\n", str);

CombiCollectionTime += RunTime();

/*      exit( 7 );*/

return 7;
}

/*
**    Combinatorial Collection from the left uses the same stacks as the plain
**    from the left collector.
*/

extern word     WordStack[];
extern expo     WordExpStack[];
extern word     GenStack[];
extern expo     GenExpStack[];
extern word     *Generators;

int             Sp;

#define STACKHEIGHT     (1 << 16)

#define CheckOverflow( n ) \
        if( (((n) << 1) >> 1) != n ) Error( "Possible integer overflow", n )

static void AddWord(expvec lhs, word w, expo we);

static void ReduceExponent(expvec ev, gen g) {

if (ev[ g ] >= Exponent[ g ]) {

  if (Power[g] != (word)0) AddWord(ev, Power[g], ev[ g ] / Exponent[ g ]);

  ev[ g ] %= Exponent[ g ];
}
}

static void StackReduceExponent(expvec ev, gen g) {

gen    h;

if (ev[ g ] >= Exponent[ g ]) {

  if (Power[ g ] != (word)0) {

   /* Need to put part of the exponent vector on the stack. */
   for (h = Commute[ g ]; h > g; h--)
    if (ev[ h ] != (expo)0) {
     if (++Sp == STACKHEIGHT) {
      Error("Out of stack space", g);
      return;
     }

     if (ev[ h ] > (expo)0) {
      WordStack[ Sp ]    = Generators[  h ];
      WordExpStack[ Sp ] = 1;
      GenExpStack[ Sp ] = ev[ h ];
     } else {
      WordStack[ Sp ]    = Generators[ -h ];
      WordExpStack[ Sp ] = 1;
      GenExpStack[ Sp ] = -ev[ h ];
     }
     ev[ h ] = (expo)0;
     GenStack[ Sp ]    = WordStack[ Sp ];
#if 0
     GenStack[ Sp ]->e; /* FIXME: statement with no effect */
#endif
    }

   AddWord(ev, Power[ g ], ev[ g ] / Exponent[ g ]);
  }

  ev[ g ] %= Exponent[ g ];
}
}

static void AddWord(expvec lhs, word w, expo we) {

gen    g;

for (; w->g != EOW && w->g <= NrPcGensList[Class + 1]; w++) {

  if (w->g > (gen)0) { g =  w->g; lhs[ g ] += we * w->e; }
  else                { g = -w->g; lhs[ g ] -= we * w->e; }

  CheckOverflow(lhs[ g ]);
  if (Exponent[ g ] != (expo)0) ReduceExponent(lhs, g);

}
}

int   CombiCollect(expvec lhs, word rhs, expo e) {

word  *ws  = WordStack;
expo  *wes = WordExpStack;
word  *gs  = GenStack;
expo  *ges = GenExpStack;
word  **C  = Conjugate;
word   *P  = Power;

word   w;
gen    ag,  g,  h,  hh;

CombiCollectionTime -= RunTime();

Sp = 0;

ws[ Sp ] = rhs;
gs[ Sp ] = rhs;
wes[ Sp ] = e;
ges[ Sp ] = rhs->e;

while (Sp >= 0)
  if ((g = gs[ Sp ]->g) != EOW && g <= NrPcGensList[Class + 1]) {

   ag = abs(g);
   if (g < 0 && Exponent[-g] != (expo)0)
    return Error("Inverse of a generator with power relation", ag);

   if (Commute[ag] == ag) {
    /* Take the exponent of the first generator from the stack not from
   the word.  Both are identical if the word is a conjugate.  They
   differ if a generator-exponent pair was pushed onto the stack.
   In that case w->e is 1 and ges[ Sp ] is the exponent. */
    w = gs[ Sp ];
    if (w->g > (gen)0) { g =  w->g; lhs[ g ] += ges[ Sp ]; }
    else                { g = -w->g; lhs[ g ] -= ges[ Sp ]; }

    CheckOverflow(lhs[ g ]);
    if (Exponent[ g ] != (expo)0) ReduceExponent(lhs, g);

    for (w++; w->g != EOW && w->g <= NrPcGensList[Class + 1]; w++) {

     if (w->g > (gen)0) { g =  w->g; lhs[ g ] += w->e; }
     else                { g = -w->g; lhs[ g ] -= w->e; }

     CheckOverflow(lhs[ g ]);
     if (Exponent[ g ] != (expo)0) ReduceExponent(lhs, g);
    }
    gs[ Sp ] = w;

    continue;
   }

   else if (3 * Wt(ag) > Class + 1) {
    /* Move the generator g to its correct position in the exponent
   vector without stacking conjugates.  Because of the class
   condition we can add the necessary *commutators* into the
   exponent vector. */
    for (h = Commute[ ag ]; h > ag; h--)
     if (lhs[ h ] != (expo)0) {
      if (lhs[ h ] > (expo)0)
       AddWord(lhs, C[  h ][ g ] + 1,  lhs[ h ] * ges[ Sp ]);
      else
       AddWord(lhs, C[ -h ][ g ] + 1, -lhs[ h ] * ges[ Sp ]);
     }

    lhs[ ag ] += sgn(g) * ges[ Sp ];
    CheckOverflow(lhs[ ag ]);

    gs[ Sp ]++;
    ges[ Sp ] = gs[ Sp ]->e;

    if (Exponent[ ag ] != (expo)0) StackReduceExponent(lhs, ag);

    continue;
   }

   else {

    lhs[ ag ] += sgn(g);

    if (--ges[ Sp ] == (expo)0) {
     /* The power of the generator g will have been moved
   completely to its correct position after this
   collection step. Therefore advance the generator
   pointer. */
     gs[ Sp ]++;
     ges[ Sp ] = gs[ Sp ]->e;
    }

    /* Add in commutators until Wt([h,g,h]) <= Class+1 */
    for (h = Commute[ ag ]; h > Commute2[ ag ]; h--)
     if (lhs[ h ] != (expo)0) {
      if (lhs[ h ] > (expo)0)
       AddWord(lhs, C[  h ][ g ] + 1,  lhs[ h ]);
      else
       AddWord(lhs, C[ -h ][ g ] + 1, -lhs[ h ]);
     }

    /* If we still have to move across generators, then we have to put
   generators onto the stack.  Find the point from where collection
   has to happen.
*/
    while (h > ag) {
     if (lhs[ h ] != (expo)0 &&
             C[h][ag] != (word)0 &&
             (C[h][ag] + 1)->g != EOW) break;
     h--;
    }

    /* Now put generator exponent pairs on the stack. */
    if (h > ag || (Exponent[ ag ] > (expo)0 &&
                   lhs[ ag ] >= Exponent[ ag ] &&
                   Power[ ag ] != (word)0)) {

     for (hh = Commute[ag]; hh > h; hh--)
      if (lhs[ hh ] != (expo)0) {
       if (++Sp == STACKHEIGHT)
        return Error("Out of stack space", ag);
       if (lhs[ hh ] > (expo)0) {
        gs[ Sp ]  = ws[ Sp ] = Generators[ hh ];
        wes[ Sp ] = 1;
        ges[ Sp ] = lhs[ hh ];
       } else {
        gs[ Sp ]  = ws[ Sp ] = Generators[ -hh ];
        wes[ Sp ] = 1;
        ges[ Sp ] = -lhs[ hh ];
       }
       lhs[hh] = (expo)0;
      }
    }

    /* Now move the generator g to its correct position
   in the exponent vector lhs. */
    for (; h > ag; h--)
     if (lhs[h] != (expo)0) {
      if (++Sp == STACKHEIGHT)
       return Error("Out of stack space", ag);
      if (lhs[ h ] > (expo)0) {
       gs[ Sp ]  = ws[ Sp ] = C[ h ][ g ];
       wes[ Sp ] = lhs[h];
       lhs[ h ] = (expo)0;
       ges[ Sp ] = gs[ Sp ]->e;
      } else {
       gs[ Sp ]  = ws[ Sp ] = C[ -h ][ g ];
       wes[ Sp ] = -lhs[h];
       lhs[ h ] = (expo)0;
       ges[ Sp ] = gs[ Sp ]->e;
      }
     }

   }

   CheckOverflow(lhs[ag]);

   if (Exponent[ag] != (expo)0)
    while (lhs[ag] >= Exponent[ag]) {
     if ((rhs = P[ ag ]) != (word)0) {
      if (++Sp == STACKHEIGHT)
       return Error("Out of stack space", ag);
      gs[ Sp ] = ws[ Sp ] = rhs;
      wes[ Sp ] = (expo)1;
      ges[ Sp ] = gs[ Sp ]->e;
     }
     lhs[ ag ] -= Exponent[ ag ];
    }
  } else {
   /* the top word on the stack has been examined completely,
   now check if its exponent is zero. */
   if (--wes[ Sp ] == (expo)0) {
    /* All powers of this word have been treated, so
   we have to move down the stack. */
    Sp--;
   } else {
    gs[ Sp ] = ws[ Sp ];
    ges[ Sp ] = gs[ Sp ]->e;
   }
  }

CombiCollectionTime += RunTime();

return 0;
}

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