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kernel: use LcmInt in order computations, fix GC bugs
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The order computation for permutations, partial permutations and
transformations now uses LcmInt(). Also, fixed a garbage collection related
bug in each: a GC could invalidate pointers to a temporary object
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@fingolfin
fingolfin committed Feb 5, 2018
1 parent 29f0678 commit 4108686
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Showing 4 changed files with 41 additions and 55 deletions.
9 changes: 9 additions & 0 deletions src/integer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -326,6 +326,15 @@ extern Obj RemInt( Obj opL, Obj opR );
extern Obj GcdInt( Obj opL, Obj opR );


/****************************************************************************
**
*F LcmInt( <opL>, <opR> ) . . . . . . . lcm of two integers
**
** 'LcmInt' returns the lcm of the two integers <opL> and <opR>.
*/
extern Obj LcmInt( Obj opL, Obj opR );


/****************************************************************************
**
*F AInvInt( <op> ) . . . . . . . . . . . . . additive inverse of an integer
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25 changes: 10 additions & 15 deletions src/permutat.c
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Expand Up @@ -2707,7 +2707,6 @@ Obj FuncOrderPerm (
UInt2 * ptKnown2; /* pointer to temporary bag */
UInt4 * ptKnown4; /* pointer to temporary bag */
UInt len; /* length of one cycle */
UInt gcd, s, t; /* gcd( len, ord ), temporaries */
UInt p, q; /* loop variables */

/* check arguments and extract permutation */
Expand Down Expand Up @@ -2747,13 +2746,11 @@ Obj FuncOrderPerm (
len++; ptKnown2[q] = 1;
}

/* compute the gcd with the previously order ord */
/* Note that since len is single precision, ord % len is to*/
gcd = len; s = INT_INTOBJ( ModInt( ord, INTOBJ_INT(len) ) );
while ( s != 0 ) {
t = s; s = gcd % s; gcd = t;
}
ord = ProdInt( ord, INTOBJ_INT( len / gcd ) );
ord = LcmInt( ord, INTOBJ_INT( len ) );

// update bag pointers, in case a garbage collection happened
ptPerm2 = CONST_ADDR_PERM2(perm);
ptKnown2 = ADDR_PERM2(TmpPerm);

}

Expand Down Expand Up @@ -2787,13 +2784,11 @@ Obj FuncOrderPerm (
len++; ptKnown4[q] = 1;
}

/* compute the gcd with the previously order ord */
/* Note that since len is single precision, ord % len is to*/
gcd = len; s = INT_INTOBJ( ModInt( ord, INTOBJ_INT(len) ) );
while ( s != 0 ) {
t = s; s = gcd % s; gcd = t;
}
ord = ProdInt( ord, INTOBJ_INT( len / gcd ) );
ord = LcmInt( ord, INTOBJ_INT( len ) );

// update bag pointers, in case a garbage collection happened
ptPerm4 = CONST_ADDR_PERM4(perm);
ptKnown4 = ADDR_PERM4(TmpPerm);

}

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24 changes: 7 additions & 17 deletions src/pperm.c
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Expand Up @@ -617,7 +617,7 @@ Obj FuncPREIMAGE_PPERM_INT(Obj self, Obj f, Obj pt)
// the least m, r such that f^m=f^m+r
Obj FuncINDEX_PERIOD_PPERM(Obj self, Obj f)
{
UInt i, len, j, pow, gcd, rank, k, deg, n;
UInt i, len, j, pow, rank, k, deg, n;
UInt2 * ptf2;
UInt4 * ptseen, *ptf4;
Obj dom, img, ord, out;
Expand Down Expand Up @@ -670,14 +670,9 @@ Obj FuncINDEX_PERIOD_PPERM(Obj self, Obj f)
len++;
ptseen[k - 1] = 0;
}
gcd = len;
j = INT_INTOBJ(ModInt(ord, INTOBJ_INT(len)));
while (j != 0) {
k = j;
j = gcd % j;
gcd = k;
}
ord = ProdInt(ord, INTOBJ_INT(len / gcd));
ord = LcmInt(ord, INTOBJ_INT(len));
// update ptseen, in case a garbage collection happened
ptseen = (UInt4 *)(ADDR_OBJ(TmpPPerm));
}
}
}
Expand Down Expand Up @@ -712,14 +707,9 @@ Obj FuncINDEX_PERIOD_PPERM(Obj self, Obj f)
len++;
ptseen[k - 1] = 0;
}
gcd = len;
j = INT_INTOBJ(ModInt(ord, INTOBJ_INT(len)));
while (j != 0) {
k = j;
j = gcd % j;
gcd = k;
}
ord = ProdInt(ord, INTOBJ_INT(len / gcd));
ord = LcmInt(ord, INTOBJ_INT(len));
// update ptseen, in case a garbage collection happened
ptseen = (UInt4 *)(ADDR_OBJ(TmpPPerm));
}
}
}
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38 changes: 15 additions & 23 deletions src/trans.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1406,7 +1406,7 @@ Obj FuncIndexPeriodOfTransformation(Obj self, Obj f)
UInt4 * seen;
UInt deg, i, pt, dist, pow, len, last_pt;
Obj ord, out;
Int s, t, gcd, cyc;
Int cyc;

if (!IS_TRANS(f)) {
ErrorQuit("IndexPeriodOfTransformation: the argument must be a "
Expand Down Expand Up @@ -1464,18 +1464,14 @@ Obj FuncIndexPeriodOfTransformation(Obj self, Obj f)
seen[pt] = 1;
}

// compute the gcd of the cycle length with the previous
// order ord
gcd = cyc;
s = INT_INTOBJ(ModInt(ord, INTOBJ_INT(cyc)));
while (s != 0) {
t = s;
s = gcd % s;
gcd = t;
}
ord = ProdInt(ord, INTOBJ_INT(cyc / gcd));
dist = len - cyc + 1;
ord = LcmInt(ord, INTOBJ_INT(cyc));

// the distance of i from the cycle in its component + 1
dist = len - cyc + 1;

// update bag pointers, in case a garbage collection happened
ptf2 = CONST_ADDR_TRANS2(f);
seen = ADDR_TRANS4(TmpTrans);
}
if (dist > pow) {
pow = dist;
Expand Down Expand Up @@ -1513,18 +1509,14 @@ Obj FuncIndexPeriodOfTransformation(Obj self, Obj f)
seen[pt] = 1;
}

// compute the gcd of the cycle length with the previous
// order ord
gcd = cyc;
s = INT_INTOBJ(ModInt(ord, INTOBJ_INT(cyc)));
while (s != 0) {
t = s;
s = gcd % s;
gcd = t;
}
ord = ProdInt(ord, INTOBJ_INT(cyc / gcd));
dist = len - cyc + 1;
ord = LcmInt(ord, INTOBJ_INT(cyc));

// the distance of i from the cycle in its component + 1
dist = len - cyc + 1;

// update bag pointers, in case a garbage collection happened
ptf4 = CONST_ADDR_TRANS4(f);
seen = ADDR_TRANS4(TmpTrans);
}
if (dist > pow) {
pow = dist;
Expand Down

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