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I am writing a piece of code in which i have to convert from double to float values. I am using boost::numeric_cast to do this conversion which will alert me of any overflow/underflow. However i am also interested in knowing if that conversion resulted in some precision loss or not.
For example
double source = 1988.1012;
float dest = numeric_cast<float>(source);
Produces dest which has value 1988.1
Is there any way available in which i can detect this kind of precision loss/rounding
459
double has 2x more precision than float. float is a 32-bit IEEE 754 single precision Floating Point Number – 1 bit for the sign, 8 bits for the exponent, and 23* for the value. float has 7 decimal digits of precision.
Floating-point decimal values generally do not have an exact binary representation. This is a side effect of how the CPU represents floating point data. For this reason, you may experience some loss of precision, and some floating-point operations may produce unexpected results.
Here double is a primitive data type its object can't be used to call the Float class method.
Double precision numbers are accurate up to sixteen decimal places but after calculations have been done there may be some rounding errors to account for. In theory this should affect no more than the last significant digit but in practice it is safer to rely upon fewer decimal places.
float dest = numeric_cast<float>(source);
double residual = source - numeric_cast<double>(dest);
Hence, residual contains the "loss" you're looking for.
154
You could cast the float back to a double and compare this double to the original - that should give you a fair indication as to whether there was a loss of precision.
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