Use custom encoding for floats in binary format

[libs/datafile.git] / source / binfloat.cpp

diff --git a/source/binfloat.cpp b/source/binfloat.cpp
new file mode 100644 (file)
index 0000000..fa4be73
--- /dev/null
+++ b/source/binfloat.cpp
@@ -0,0 +1,72 @@
+#include <cmath>
+#include "binfloat.h"
+
+using namespace std;
+
+
+namespace Msp {
+namespace DataFile {
+
+BinFloat BinFloat::explode(UInt64 value, const Bits &bits)
+{
+       UInt64 mantissa_mask = (UInt64(1)<<bits.mantissa)-1;
+       int exponent_mask = (1<<bits.exponent)-1;
+
+       BinFloat bf;
+       // Extract biased exponent and sign
+       bf.exponent = (value>>bits.mantissa)&exponent_mask;
+       bf.sign = value>>(bits.mantissa+bits.exponent);
+       bf.infinity = (bf.exponent==exponent_mask);
+
+       if(bf.exponent==0 || bf.infinity)
+               // Zeroes and infinities have zero mantissa
+               bf.mantissa = 0;
+       else
+       {
+               // Extract mantissa, add the implied one and align it to high bits
+               bf.mantissa = (value&mantissa_mask) | (UInt64(1)<<bits.mantissa);
+               bf.mantissa <<= 63-bits.mantissa;
+       }
+
+       // Unbias the exponent
+       bf.exponent -= exponent_mask>>1;
+
+       return bf;
+}
+
+UInt64 BinFloat::compose(const Bits &bits)
+{
+       UInt64 mantissa_mask = (UInt64(1)<<bits.mantissa)-1;
+       int exponent_mask = (1<<bits.exponent)-1;
+
+       int biased_exponent = exponent+(exponent_mask>>1);
+       // Shift down and round the mantissa
+       UInt64 rounded_mantissa = ((mantissa>>(62-bits.mantissa))+1)>>1;
+       // If the integer part is greater than one, we need to use a higher exponent
+       if((rounded_mantissa>>bits.mantissa)>1)
+               ++biased_exponent;
+
+       if(biased_exponent>=exponent_mask || infinity)
+               // Overflow, return infinity
+               return UInt64(sign<<bits.exponent | exponent_mask)<<bits.mantissa;
+       else if(biased_exponent<=0 || !mantissa)
+               // Underflow, return zero
+               return 0;
+       else
+       {
+               UInt64 value = rounded_mantissa&mantissa_mask;
+               value |= UInt64(biased_exponent)<<bits.mantissa;
+               value |= UInt64(sign)<<(bits.mantissa+bits.exponent);
+               return value;
+       }
+}
+
+
+// exponent = log_2(bits)*3-7
+BinFloat::Bits::Bits(unsigned bits):
+       exponent(log(bits)*4.3281-7),
+       mantissa(bits-exponent-1)
+{ }
+
+} // namespace DataFile
+} // namespace Msp