Background on Floating-Point
Floating-point numbers are represented in the following form:
significant x 2^exponent
where significant (or mantissa) and exponent are integers.
The FP32 (32-bit) floating-point format uses 8 bits for exponents. FP32 exponents range from −126 to +127; exponents of −127 (all 0s) and +128 (all 1s) are reserved for special numbers. Similarly, the FP64 (64-bit) floating-point format uses 11 bits for exponents. FP64 exponents range from −1022 to +1023; exponents of −1023 (all 0s) and +1024 (all 1s) are reserved for special numbers.
Exponent Usage Histograms
FPChecker can create histograms of the exponent usage in your application. Understanding the exponent usage in your application allows you to understand the numerical magnitudes your code operates on.
To enable exponent usage histograms, define the following variable in your compilation flags:
-DFPC_EXPONENT_USAGE
Reports
Once you run the application, traces will be saved in the .fpc_log directory (one trace per process). To generate a report, execute the following command in the directory where the application ran:
$ fpc-create-usage-report
A directory called fpc-report will be generated with report. Open index.html in that directory.
Plots
Histogram plots show the number of times a range of exponents were used in the floating-point operations of your application. The report provides a histogram plot for the entire program and different histogram plots for the application files.
Sample Reports
These are some sample reports from open-source applications: