tdf#94924: Return correct result 0 from OpenCL MIN and MAX when all args empty

Used the same style as existing code, added a new virtual isMinOrMax()
and add some special casing in Reduction::GenSlidingWindowFunction(),
and fsim_count() and fmax_count() functions that count how many
non-NaN numbers we actually see. As such, I am not sure at all that
this is an ideal way to do this, but will have to do for now.

Change-Id: I846a8d24f4563f8fae1a45971a4ce202ed918487

sc/source/core/opencl/formulagroupcl.cxx

@@ -63,6 +63,18 @@ static const char* publicFunc =
  "    (*p) += t?0:1;\n"
  "    return t?b:a+b;\n"
  "}\n"
+ "double fmin_count(double a, double b, __private int *p) {\n"
+ "    double result = fmin(a, b);\n"
+ "    bool t = isnan(result);\n"
+ "    (*p) += t?0:1;\n"
+ "    return result;\n"
+ "}\n"
+ "double fmax_count(double a, double b, __private int *p) {\n"
+ "    double result = fmax(a, b);\n"
+ "    bool t = isnan(result);\n"
+ "    (*p) += t?0:1;\n"
+ "    return result;\n"
+ "}\n"
  "double fsum(double a, double b) { return isNan(a)?b:a+b; }\n"
  "double legalize(double a, double b) { return isNan(a)?b:a;}\n"
  "double fsub(double a, double b) { return a-b; }\n"
@@ -1696,7 +1708,7 @@ public:
         ss << ") {\n";
         ss << "double tmp = " << GetBottom() << ";\n";
         ss << "int gid0 = get_global_id(0);\n";
-        if (isAverage())
+        if (isAverage() || isMinOrMax())
             ss << "int nCount = 0;\n";
         ss << "double tmpBottom;\n";
         unsigned i = vSubArguments.size();
@@ -1783,12 +1795,17 @@ public:
             ss <<
                 "if (nCount==0)\n"
                 "    return CreateDoubleError(errDivisionByZero);\n";
+        else if (isMinOrMax())
+            ss <<
+                "if (nCount==0)\n"
+                "    return 0;\n";
         ss << "return tmp";
         if (isAverage())
             ss << "*pow((double)nCount,-1.0)";
         ss << ";\n}";
     }
     virtual bool isAverage() const { return false; }
+    virtual bool isMinOrMax() const { return false; }
     virtual bool takeString() const override { return false; }
     virtual bool takeNumeric() const override { return true; }
 };
@@ -2203,12 +2220,13 @@ class OpMin : public Reduction
 public:
     OpMin( int nResultSize ) : Reduction(nResultSize) {}
 
-    virtual std::string GetBottom() override { return "MAXFLOAT"; }
+    virtual std::string GetBottom() override { return "NAN"; }
     virtual std::string Gen2( const std::string& lhs, const std::string& rhs ) const override
     {
-        return "fmin(" + lhs + "," + rhs + ")";
+        return "fmin_count(" + lhs + "," + rhs + ", &nCount)";
     }
     virtual std::string BinFuncName() const override { return "min"; }
+    virtual bool isMinOrMax() const override { return true; }
 };
 
 class OpMax : public Reduction
@@ -2216,12 +2234,13 @@ class OpMax : public Reduction
 public:
     OpMax( int nResultSize ) : Reduction(nResultSize) {}
 
-    virtual std::string GetBottom() override { return "-MAXFLOAT"; }
+    virtual std::string GetBottom() override { return "NAN"; }
     virtual std::string Gen2( const std::string& lhs, const std::string& rhs ) const override
     {
-        return "fmax(" + lhs + "," + rhs + ")";
+        return "fmax_count(" + lhs + "," + rhs + ", &nCount)";
     }
     virtual std::string BinFuncName() const override { return "max"; }
+    virtual bool isMinOrMax() const override { return true; }
 };
 
 class OpSumProduct : public SumOfProduct