[Mlir-commits] [mlir] [MLIR][Presburger] Implement function to evaluate the number of terms in a generating function. (PR #78078)

[Arjun P]

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@@ -245,3 +245,253 @@ QuasiPolynomial mlir::presburger::detail::getCoefficientInRationalFunction(
   }
   return coefficients[power].simplify();
 }
+
+static std::vector<Fraction> convolution(std::vector<Fraction> a,
+                                         std::vector<Fraction> b) {
+  // The length of the convolution is the maximum of the lengths
+  // of the two sequences. We pad the shorter one with zeroes.
+  unsigned convlen = std::max(a.size(), b.size());
+  for (unsigned k = a.size(); k < convlen; ++k)
+    a.push_back(0);
+  for (unsigned k = b.size(); k < convlen; ++k)
+    b.push_back(0);
+
+  std::vector<Fraction> convolution;
+  convolution.reserve(convlen);
+  convolution.clear();
+  for (unsigned k = 0; k < convlen; ++k) {
+    Fraction sum(0, 1);
+    for (unsigned l = 0; l <= k; ++l)
+      sum = sum + a[l] * b[k - l];
+    convolution.push_back(sum);
+  }
+  return convolution;
+}
+
+/// Substitute x_i = (s+1)^μ_i in one term of a generating function,
+/// returning
+/// a quasipolynomial which represents the exponent of the numerator
+/// of the result, and
+/// a vector which represents the exponents of the denominator of the
+/// result.
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Superty wrote:

explain what the representation you are substituting into is, in terms of v and ds

https://github.com/llvm/llvm-project/pull/78078