From 1f2695d4280d322f92211af4e246239c8055c91a Mon Sep 17 00:00:00 2001
From: Stefan Wahren <info@lategoodbye.de>
Date: Fri, 6 Apr 2012 17:42:55 +0200
Subject: [PATCH] Added support for 4 byte floating point numbers

---
 mbus/mbus-protocol.c | 60 +++++++++++++++++++++++++++++++++++++++++++-
 mbus/mbus-protocol.h |  2 ++
 2 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/mbus/mbus-protocol.c b/mbus/mbus-protocol.c
index 3cb9b46..2cbd014 100644
--- a/mbus/mbus-protocol.c
+++ b/mbus/mbus-protocol.c
@@ -10,6 +10,7 @@
 //------------------------------------------------------------------------------
 
 #include <assert.h>
+#include <math.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -438,6 +439,53 @@ mbus_data_int_encode(u_char *int_data, size_t int_data_size, int value)
     return -1;
 }
 
+//------------------------------------------------------------------------------
+///
+/// Decode float data 
+///
+/// see also http://en.wikipedia.org/wiki/Single-precision_floating-point_format
+///
+//------------------------------------------------------------------------------
+float
+mbus_data_float_decode(u_char *float_data)
+{
+    float val = 0.0f;
+    long temp = 0, fraction;
+    int sign,exponent;
+    size_t i;
+    
+    if (float_data)
+    {
+        for (i = 4; i > 0; i--)
+        {
+            temp = (temp << 8) + float_data[i-1];
+        }
+        
+        // first bit = sign bit
+        sign     = (temp >> 31) ? -1 : 1;
+  
+        // decode 8 bit exponent
+        exponent = ((temp & 0x7F800000) >> 23) - 127;
+  
+        // decode explicit 23 bit fraction
+        fraction = temp & 0x007FFFFF;
+  
+        if ((exponent != -127) &&
+            (exponent != 128))
+        {
+            // normalized value, add bit 24 
+            fraction |= 0x800000;
+        }
+  
+        // calculate float value
+        val = (float) sign * fraction * pow(2.0f, -23.0f) * (1 << exponent);
+
+        return val;    
+    }
+
+    return -1.0;
+}
+
 //------------------------------------------------------------------------------
 ///
 /// Decode string data.
@@ -1626,6 +1674,7 @@ mbus_data_record_decode(mbus_data_record *record)
     {
         int val;
         long val2;
+        float val3;
         struct tm time;
             
         switch (record->drh.dib.dif & 0x0F)
@@ -1710,7 +1759,16 @@ mbus_data_record_decode(mbus_data_record *record)
 
                 break;  
 
-            // case 0x05:
+            case 0x05: // 4 Byte Real (32 bit)
+            
+                val3 = mbus_data_float_decode(record->data);
+                
+                snprintf(buff, sizeof(buff), "%f", val3);
+                
+                if (debug)
+                    printf("%s: DIF 0x%.2x was decoded using 4 byte Real\n", __PRETTY_FUNCTION__, record->drh.dib.dif);    
+                    
+                break;
 
             case 0x06: // 6 byte integer (48 bit)
 
diff --git a/mbus/mbus-protocol.h b/mbus/mbus-protocol.h
index f5b2fa5..c66cd5d 100644
--- a/mbus/mbus-protocol.h
+++ b/mbus/mbus-protocol.h
@@ -512,6 +512,8 @@ long mbus_data_bcd_decode(u_char *bcd_data, size_t bcd_data_size);
 int  mbus_data_int_decode(u_char *int_data, size_t int_data_size);
 long mbus_data_long_decode(u_char *int_data, size_t int_data_size);
 
+float mbus_data_float_decode(u_char *float_data);
+
 void mbus_data_tm_decode(struct tm *t, u_char *t_data, size_t t_data_size);
 
 void mbus_data_str_decode(u_char *dst, const u_char *src, size_t len);