Converting 24 bit integer (2s complement) to 32 bit integer in C++

Question

The dataFile.bin is a binary file with 6-byte records. The first 3 bytes of each record contain the latitude and the last 3 bytes contain the longitude. E

Answer 1

When an unsigned char is casted to an int the higher order bits are filled with 0's

When a signed char is casted to a casted int, the sign bit is extended. ie:

int x;
char y;
unsigned char z;
y=0xFF
z=0xFF
x=y;
/*x will be 0xFFFFFFFF*/
x=z;
/*x will be 0x000000FF*/

So, your algorithm, uses 0xFF as a mask to remove C' sign extension, ie

0xFF == 0x000000FF
0xABCDEF10 & 0x000000FF == 0x00000010

Then uses bit shifts and logical ands to put the bits in their proper place.

Lastly checks the most significant bit (newInt & 0x00800000) > 0 to decide if completing with 0's or ones the highest byte.