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flint: perf: use mpoly for sparse univariate computations #729

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flint: perf: use mpoly for sparse univariate computations #729

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24 changes: 23 additions & 1 deletion sources/flintinterface.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,13 @@ static_assert(sizeof(slong) == sizeof(int64_t), "flint interface expects slong i
#] Types
*/

/*
* FLINT's univariate poly has a dense representation. For sufficiently sparse polynomials it is
* faster to use mpoly instead, which is sparse. For a density <= this threshold we switch, where
* the density defined as is "number of terms" / "maximum degree".
*/
#define UNIVARIATE_DENSITY_THR 0.02f

/*
#[ flint::cleanup :
*/
Expand Down Expand Up @@ -1061,7 +1068,9 @@ flint::var_map_t flint::get_variables(const vector <WORD *> &es, const bool with
const bool sort_vars) {

int32_t num_vars = 0;
// To be used if we sort by highest degree, as the polu code does.
// We count the total number of terms to determine "density".
uint32_t num_terms = 0;
// To be used if we sort by highest degree, as the poly code does.
vector<int32_t> degrees;
var_map_t var_map;

Expand All @@ -1071,8 +1080,10 @@ flint::var_map_t flint::get_variables(const vector <WORD *> &es, const bool with

// fast notation
if ( *e == -SNUMBER ) {
num_terms++;
}
else if ( *e == -SYMBOL ) {
num_terms++;
if ( !var_map.count(e[1]) ) {
var_map[e[1]] = num_vars++;
degrees.push_back(1);
Expand All @@ -1087,6 +1098,7 @@ flint::var_map_t flint::get_variables(const vector <WORD *> &es, const bool with
}
else {
for ( WORD i = with_arghead ? ARGHEAD:0; with_arghead ? i < e[0]:e[i] != 0; i += e[i] ) {
num_terms++;
if ( i+1 < i+e[i]-ABS(e[i+e[i]-1]) && e[i+1] != SYMBOL ) {
MLOCK(ErrorMessageLock);
MesPrint("ERROR: polynomials and polyratfuns must contain symbols only");
Expand Down Expand Up @@ -1152,6 +1164,16 @@ flint::var_map_t flint::get_variables(const vector <WORD *> &es, const bool with
}
}

if ( var_map.size() == 1 ) {
// In the univariate case, if the polynomials are sufficiently sparse force the use of the
// multivariate routines, which use a sparse representation, by adding a dummy map entry.
if ( (float)num_terms <= UNIVARIATE_DENSITY_THR * (float)degrees[0] ) {
// -1 will never be a symbol code. Built-in symbols from 0 to 19, and 20 is the first
// user symbol.
var_map[-1] = num_vars;
}
}

return var_map;
}
/*
Expand Down