Changeset 1001 for cpp

Timestamp:

07/14/20 00:21:40 (4 years ago)

Author:

Maciej Komosinski

Message:

Another attempt to rounding floating-point values with desired precision

File:

• cpp/common/nonstd_math.cpp (modified) (1 diff)

cpp/common/nonstd_math.cpp

@@ -15 +15 @@
 }
 
-std::string doubleToString(double x, int precision)
+
+std::string doubleToString(double x, int precision) //waiting for a proper, native C++ solution
 {
-        std::stringstream ss;
-        ss << std::fixed;
-        ss.precision(precision); //set the number of places after decimal
-        ss << x;
-        return ss.str();
+        std::stringstream ss; //or for pre-allocated buffer, sprintf(s, "%.*f", precision, x);
+        std::string str;
+        if (fabs(x) < 1e8) //limiting the precision of huge fp values makes little sense - better use scientific notation, unless we want a looong number
+        {
+                ss << std::fixed;
+                ss.precision(precision); //set the number of places after decimal
+                ss << x;
+                str = ss.str();
+                char *s = str.data(); //now we will be operating directly on the internal std::string buffer            
+                for (int i = str.length() - 1, end = str.length(); i >= 0; i--) //remove trailing zeros, and maybe also '.'
+                {
+                        if (s[i] == '0')
+                        {
+                                if (end == i + 1)
+                                        end = i;
+                        }
+                        else if (s[i] == '.')
+                        {
+                                if (end == i + 1)
+                                        end = i;
+                                s[end] = '\0';
+                                break;
+                        }
+                }
+        }
+        else
+        {
+                ss << x;
+                str = ss.str();
+        }
+        //printf("%.17g and %d decimals: %s\n", x, precision, str.c_str());
+        return str;
 }