Use custom encoding for floats in binary format

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

diff --git a/source/binarywriter.cpp b/source/binarywriter.cpp
index 9c9c893e890354bc1198c0cfdd4603ede61b3270..ffdc040f115565bbb18239ee9f2c14a137507fde 100644 (file)
--- a/source/binarywriter.cpp
+++ b/source/binarywriter.cpp
@@ -1,5 +1,7 @@
+#include <limits>
 #include <msp/core/maputils.h>
 #include "binarywriter.h"
+#include "binfloat.h"
 #include "statement.h"
 
 using namespace std;
@@ -10,10 +12,23 @@ namespace DataFile {
 BinaryWriter::BinaryWriter(IO::Base &o):
        WriterMode(o),
        next_kwd_id(1),
-       next_str_id(1)
+       next_str_id(1),
+       float_precision(32)
 {
        dict[DictEntry("__kwd", "iss")] = -1;
        dict[DictEntry("__str", "is")] = -2;
+       dict[DictEntry("__flt", "i")] = -3;
+}
+
+void BinaryWriter::set_float_precision(unsigned fp)
+{
+       if(fp<16 || fp>64 || fp%8)
+               throw invalid_argument("BinaryWriter::set_float_precision");
+       float_precision = fp;
+       Statement fst;
+       fst.keyword = "__flt";
+       fst.args.push_back(float_precision);
+       write_(fst);
 }
 
 void BinaryWriter::write(const Statement &st)
@@ -116,20 +131,44 @@ void BinaryWriter::write_string(const StringType::Store &s)
 
 void BinaryWriter::write_float(FloatType::Store f)
 {
-       union
+       BinFloat bf;
+
+       if(numeric_limits<FloatType::Store>::is_iec559)
+               bf = BinFloat::explode_iec559(f);
+       else
        {
-               float v;
-               char d[sizeof(float)];
-       };
-
-       v = f;
-#if BYTE_ORDER == LITTLE_ENDIAN
-       for(unsigned i = sizeof(float); i--;)
-               out.put(d[i]);
-#else
-       for(unsigned i = 0; i<sizeof(float); ++i)
-               out.put(d[i]);
-#endif
+               /* The structure of the float is unknown, so we must use arithmetic to
+               reduce it to components. */
+               bf.sign = f<0;
+               bf.exponent = 0;
+               bf.mantissa = 0;
+
+               if(f<0)
+                       f = -f;
+               if(!(f+f>f))
+                       bf.infinity = true;
+               else if(f!=0)
+               {
+                       for(; f<1; f*=2)
+                               --bf.exponent;
+                       for(; f>=2; f/=2)
+                               ++bf.exponent;
+                       for(unsigned i=0; i<64; ++i)
+                       {
+                               bf.mantissa <<= 1;
+                               if(f>=1)
+                               {
+                                       bf.mantissa |= 1;
+                                       f -= 1;
+                               }
+                               f *= 2;
+                       }
+               }
+       }
+
+       UInt64 encoded = bf.compose(float_precision);
+       for(unsigned i=float_precision/8; i--; )
+               out.put((encoded>>(i*8))&0xFF);
 }
 
 void BinaryWriter::write_symbol(const SymbolType::Store &s)