Changeset 979 for cpp/common/nonstd_math.cpp

Timestamp:

07/08/20 01:53:39 (4 years ago)

Author:

Maciej Komosinski

Message:

Improved float-rounding functions, follow-up to r970

File:

• cpp/common/nonstd_math.cpp (modified) (3 diffs)

cpp/common/nonstd_math.cpp

@@ -4 +4 @@
 
 #include "nonstd_math.h"
-#ifdef USE_PRINTFLOAT_DRAGON4
 #include <PrintFloat/PrintFloat.h>
-#else
 #include <sstream>
-#endif
+#include <algorithm>    // std::min
 
 RandomGenerator &rndGetInstance()
@@ -16 +14 @@
 }
 
+std::string doubleToString(double x, int precision)
+{
+        std::stringstream ss;
+        ss << std::fixed;
+        ss.precision(precision); //set the number of places after decimal
+        ss << x;
+        return ss.str();
+}
+
 int doubleToString(double x, int precision, char *buffer, int bufferlen)
 {
+        // C++ in 2020 and the impossible challenge https://stackoverflow.com/questions/277772/avoid-trailing-zeroes-in-printf
+        if (precision < 0)
+        {
+                // The "g" format does not allow to use the number of decimal places after the decimal point. Dragon4 on the other hand fills in unnecessary trailinig zeros... so both are good only for "full precision".
 #ifdef USE_PRINTFLOAT_DRAGON4
-        return PrintFloat64(buffer, bufferlen, x,
-                ((x < -1e17) || (x > 1e17) || ((x < 1e-4) && (x > -1e-4) && (x != 0.0)))
-                ? PrintFloatFormat_Scientific : PrintFloatFormat_Positional,
-                precision); //http://www.ryanjuckett.com/programming/printing-floating-point-numbers/
+                return PrintFloat64(buffer, bufferlen, x,
+                        ((x < -1e17) || (x > 1e17) || ((x < 1e-4) && (x > -1e-4) && (x != 0.0)))
+                        ? PrintFloatFormat_Scientific : PrintFloatFormat_Positional,
+                        precision); //http://www.ryanjuckett.com/programming/printing-floating-point-numbers/
 #else
-        char format[10];
-        sprintf(format, "%%.%dg", precision < 0 ? 17 : precision); //https://stackoverflow.com/questions/16839658/printf-width-specifier-to-maintain-precision-of-floating-point-value
-        return sprintf(buffer, format, x);
+                return sprintf(buffer, "%.17g", x);
 #endif
+        }
+        else
+        {
+                std::string s = doubleToString(x, precision);
+                strncpy(buffer, s.c_str(), std::min(bufferlen, (int)s.length() + 1));
+                buffer[bufferlen - 1] = 0; //ensure the string is truncated
+                return s.length();
+        }
 }
 
@@ -33 +50 @@
 double round(const double x, const int precision)
 {
-#ifdef USE_PRINTFLOAT_DRAGON4
-        char buffer[30];
-        doubleToString(x, precision, buffer, 30);
-        double rounded = strtod(buffer, NULL);
-#else
-        std::stringstream ss;
-        ss << std::fixed;
-        ss.precision(precision); // set the number of places after decimal
-        ss << x;
-        double rounded = stod(ss.str());
-#endif
+        double rounded = std::stod(doubleToString(x, precision));
         //printf("%d  %20g \t %20g\n", precision, x, rounded); //for debugging
         return rounded;