Convert binary two's complement data into integer in objective-c

Question

I have some binary data (twos complement) coming from an accelerometer and I need to convert it to an integer. Is there a standard library function which does this, or do I

Answer 1

Something like:

const int8_t* bytes = (const int8_t*) [nsDataObject bytes];

int32_t x = (bytes[0] << 8) + (0x0FF & bytes[1]);
x = x << 16;
x = x >> 16;

int32_t y = (bytes[2] << 8) + (0x0FF & bytes[3]);
y = y << 16;
y = y >> 16;

int32_t z = (bytes[4] << 8) + (0x0FF & bytes[5]);
z = z << 16;
z = z >> 16;

This assumes that the values really are "big-endian" as suggested in the question.