Generic bitfield handler functions.

# Conflicts:
#	lib/dtscmeta.cpp

lib/bitfields.cpp

@@ -0,0 +1,64 @@
+#include "bitfields.h"
+
+/// Takes a pointer, offset bitcount and data bitcount, returning the unsigned int read from the givens.
+/// offsetBits may be > 7, in which case offsetBits / 8 is added to the pointer automatically.
+/// This function assumes Most Significant Bits first.
+/// If dataBits > 64, only the last 64 bits are returned.
+unsigned long long Bit::getMSB(char * pointer, unsigned int offsetBits, unsigned int dataBits){
+  //If the offset is a whole byte or more, add the whole bytes to the pointer instead.
+  pointer += offsetBits >> 3;
+  //The offset is now guaranteed less than a whole byte.
+  offsetBits &= 0x07;
+  unsigned long long retVal = 0;
+  //Now we parse the remaining bytes
+  while (dataBits){
+    //Calculate how many bits we're reading from this byte
+    //We assume all except for the offset
+    unsigned int curBits = 8 - offsetBits;
+    //If that is too much, we use the remainder instead
+    if (curBits > dataBits){
+      curBits = dataBits;
+    }
+    //First, shift the current return value by the amount of bits we're adding
+    retVal <<= curBits;
+    //Next, add those bits from the current pointer position at the correct offset, increasing the pointer by one
+    retVal |= ((int)(*(pointer++)) << offsetBits) >> (8 - curBits);
+    //Finally, set the offset to zero and remove curBits from dataBits.
+    offsetBits = 0;
+    dataBits -= curBits;
+  }//Loop until we run out of dataBits, then return the result
+  return retVal;
+}
+
+/// Takes a pointer, offset bitcount and data bitcount, setting to given value.
+/// offsetBits may be > 7, in which case offsetBits / 8 is added to the pointer automatically.
+/// This function assumes Most Significant Bits first.
+/// WARNING: UNFINISHED. DO NOT USE.
+/// \todo Finish writing this - untested atm.
+void Bit::setMSB(char * pointer, unsigned int offsetBits, unsigned int dataBits, unsigned long long value){
+  //Set the pointer to the last byte we need to be setting
+  pointer += (offsetBits + dataBits) >> 3;
+  //The offset is now guaranteed less than a whole byte.
+  offsetBits = (offsetBits + dataBits) & 0x07;
+  unsigned long long retVal = 0;
+  //Now we set the remaining bytes
+  while (dataBits){
+    //Calculate how many bits we're setting in this byte
+    //We assume all that will fit in the current byte
+    unsigned int curBits = offsetBits;
+    //If that is too much, we use the remainder instead
+    if (curBits > dataBits){
+      curBits = dataBits;
+    }
+    //Set the current pointer position at the correct offset, increasing the pointer by one
+    retVal |= ((int)(*(pointer++)) << offsetBits) >> (8 - curBits);
+    *pointer = (((*pointer) << offsetBits) >> offsetBits) | ((value & 0xFF) << (8 - offsetBits));
+    --pointer;
+    //Finally, shift the current value by the amount of bits we're adding
+    value >>= offsetBits;
+    //... and set the offset to eight and remove curBits from dataBits.
+    offsetBits = 8;
+    dataBits -= curBits;
+  }//Loop until we run out of dataBits, then return the result
+}
+