Revision 5:0a0315f0f34e, committed 2012-09-12

Comitter:

gltest26

Date:

Wed Sep 12 22:56:04 2012 +0000

Parent:

4:155c44407af5

Child:

6:a7ad6046824c

Commit message:

Made byte ordering and sign extending portable.

Changed in this revision

--- a/ITG3200.cpp	Wed Sep 12 15:23:29 2012 +0000
+++ b/ITG3200.cpp	Wed Sep 12 22:56:04 2012 +0000
@@ -205,14 +205,7 @@
     
     i2c_.read(I2C_ADDRESS, rx, 2);
     
-    // Readings are expressed in 16bit 2's complement, so we must first
-    // concatenate two bytes to make a word and sign extend it to obtain
-    // correct negative values.
-    // ARMCC compiles char as unsigned, which means no sign extension is
-    // performed during bitwise operations to chars. But we should make sure
-    // that lower byte won't extend its sign past upper byte for other
-    // compilers if we want to keep it portable.
-    return int16_t(((unsigned)rx[0] << 8) | (unsigned)rx[1]);
+    return swapExtend(rx);
 }
 
 float ITG3200::getTemperature(){
@@ -231,7 +224,7 @@
     i2c_.read(I2C_ADDRESS, rx, 6);
     
     for(int i = 0; i < 3; i++)
-        readings[i] = int16_t((unsigned) rx[i * 2 + 0] << 8) | ((unsigned) rx[i * 2 + 1]);
+        readings[i] = swapExtend(&rx[i * 2]);
 }
 
 char ITG3200::getPowerManagement(void){

--- a/ITG3200.h	Wed Sep 12 15:23:29 2012 +0000
+++ b/ITG3200.h	Wed Sep 12 22:56:04 2012 +0000
@@ -425,6 +425,22 @@
 
     I2C i2c_;
 
+    /**
+     * Converts big-endian 2's complement byte pair to native byte order of
+     * the CPU and then sign extend it to the CPU's register size.
+     *
+     * Implemented here to make the compiler inline expand it.
+     */
+    int swapExtend(const char rx[2]){
+        // Readings are expressed in 16bit 2's complement, so we must first
+        // concatenate two bytes to make a word and sign extend it to obtain
+        // correct negative values.
+        // ARMCC compiles char as unsigned, which means no sign extension is
+        // performed during bitwise operations to chars. But we should make sure
+        // that lower byte won't extend its sign past upper byte for other
+        // compilers if we want to keep it portable.
+        return int16_t(((unsigned char)rx[0] << 8) | (unsigned char)rx[1]);
+    }
 };