Extract offset bits from bit field

offsetbits.c

#include <stdint.h>
#include <stdio.h>
#include <inttypes.h>

uint32_t get_offset_bits(uint8_t *data, uint32_t offset, uint32_t count)
{
	int shft;
	uint32_t ret, byte;
	
	byte = offset / 8;
	shft = offset & 7;

	ret = (((uint32_t)data[byte + 0]) << (shft + 24));

	if (count + shft > 8)
		ret |= (((uint32_t)data[byte + 1]) << (shft + 16));
	if (count + shft > 16)
		ret |= (((uint32_t)data[byte + 2]) << (shft +  8));
	if (count + shft > 24)
		ret |= (((uint32_t)data[byte + 3]) << (shft +  0));
	if (count + shft > 32)
		ret |= (((uint32_t)data[byte + 4]) << (shft -  8));

	return ret >> (32 - count);
}

int main(void)
{
	uint8_t test[] = {0xff, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03};
	printf("%"PRIx32"\n", get_offset_bits(test, 0, 32));
	printf("%"PRIx32"\n", get_offset_bits(test, 62, 2));
}