Move mju_combineSparseCount into engine_util_sparse.

PiperOrigin-RevId: 561025741
Change-Id: I0bdc48554928fc4545a38a8cea3bdeb593bd7ecd

src/engine/engine_core_constraint.c

@@ -1351,33 +1351,6 @@ void mj_makeImpedance(const mjModel* m, mjData* d) {
 
 //------------------------------------- constraint counting ----------------------------------------
 
-// count the number of non-zeros in the sum of two sparse vectors
-int mju_combineSparseCount(int a_nnz, int b_nnz, const int* a_ind, const int* b_ind) {
-  int a = 0, b = 0, c_nnz = 0;
-
-  // count c_nnz: nonzero indices common to both a and b
-  while (a < a_nnz && b < b_nnz) {
-    // common index, increment everything
-    if (a_ind[a] == b_ind[b]) {
-      c_nnz++;
-      a++;
-      b++;
-    }
-
-    // update smallest index
-    else if (a_ind[a] < b_ind[b]) {
-      a++;
-    } else {
-      b++;
-    }
-  }
-
-  // union minus the intersection
-  return a_nnz + b_nnz - c_nnz;
-}
-
-
-
 // count the non-zero columns in the Jacobian difference of two bodies
 static int mj_jacDifPairCount(const mjModel* m, int* chain,
                               int b1, int b2, int issparse) {

src/engine/engine_core_constraint.h

@@ -93,13 +93,6 @@ void mj_diagApprox(const mjModel* m, mjData* d);
 // compute efc_R, efc_D, efc_KDIP, adjust diagApprox
 void mj_makeImpedance(const mjModel* m, mjData* d);
 
-
-//------------------------- constraint counting
-
-// count the number of non-zeros in the sum of two sparse vectors
-MJAPI int mju_combineSparseCount(int a_nnz, int b_nnz, const int* a_ind, const int* b_ind);
-
-
 //---------------------------- top-level API for constraint construction ---------------------------
 
 // main driver: call all functions above

src/engine/engine_util_sparse.c

@@ -207,6 +207,33 @@ static int mju_compare(const int* vec1, const int* vec2, int n) {
 
 
 
+// count the number of non-zeros in the sum of two sparse vectors
+int mju_combineSparseCount(int a_nnz, int b_nnz, const int* a_ind, const int* b_ind) {
+  int a = 0, b = 0, c_nnz = 0;
+
+  // count c_nnz: nonzero indices common to both a and b
+  while (a < a_nnz && b < b_nnz) {
+    // common index, increment everything
+    if (a_ind[a] == b_ind[b]) {
+      c_nnz++;
+      a++;
+      b++;
+    }
+
+    // update smallest index
+    else if (a_ind[a] < b_ind[b]) {
+      a++;
+    } else {
+      b++;
+    }
+  }
+
+  // union minus the intersection
+  return a_nnz + b_nnz - c_nnz;
+}
+
+
+
 // combine two sparse vectors: dst = a*dst + b*src, return nnz of result
 int mju_combineSparse(mjtNum* dst, const mjtNum* src, mjtNum a, mjtNum b,
                       int dst_nnz, int src_nnz, int* dst_ind, const int* src_ind,

src/engine/engine_util_sparse.h

@@ -51,6 +51,9 @@ MJAPI void mju_mulMatVecSparse(mjtNum* res, const mjtNum* mat, const mjtNum* vec
 MJAPI void mju_compressSparse(mjtNum* mat, int nr, int nc,
                               int* rownnz, int* rowadr, int* colind);
 
+// count the number of non-zeros in the sum of two sparse vectors
+MJAPI int mju_combineSparseCount(int a_nnz, int b_nnz, const int* a_ind, const int* b_ind);
+
 // combine two sparse vectors: dst = a*dst + b*src, return nnz of result
 int mju_combineSparse(mjtNum* dst, const mjtNum* src, mjtNum a, mjtNum b,
                       int dst_nnz, int src_nnz, int* dst_ind, const int* src_ind,