#include <stdlib.h>
#include <stddef.h>

// This GETBIT is supposed to work on little endian 
// 32bit systems. The algorithm will definitely need
// some fixing on other systems, but it might not be
// a problem since the nrv2b binary behaves the same..

#define GETBIT(bb, src, ilen) \
    (bc > 0 ? ((bb>>--bc)&1) : (bc=31,\
    bb=*(const uint32_t *)((src)+ilen),ilen+=4,(bb>>31)&1))

static void unrv2b(uint8_t * src, uint8_t * dst)
{
	unsigned long ilen = 0, olen = 0, last_m_off = 1;
	uint32_t bb = 0;
	unsigned bc = 0;
	const uint8_t *m_pos;

	// skip length
	src += 4;

	for (;;) {
		unsigned int m_off, m_len;
		while (GETBIT(bb, src, ilen)) {
			dst[olen++] = src[ilen++];
		}

		m_off = 1;
		do {
			m_off = m_off * 2 + GETBIT(bb, src, ilen);
		} while (!GETBIT(bb, src, ilen));
		if (m_off == 2) {
			m_off = last_m_off;
		} else {
			m_off = (m_off - 3) * 256 + src[ilen++];
			if (m_off == 0xffffffffU)
				break;
			last_m_off = ++m_off;
		}

		m_len = GETBIT(bb, src, ilen);
		m_len = m_len * 2 + GETBIT(bb, src, ilen);
		if (m_len == 0) {
			m_len++;
			do {
				m_len = m_len * 2 + GETBIT(bb, src, ilen);
			} while (!GETBIT(bb, src, ilen));
			m_len += 2;
		}
		m_len += (m_off > 0xd00);

		m_pos = dst + olen - m_off;
		dst[olen++] = *m_pos++;
		do {
			dst[olen++] = *m_pos++;
		} while (--m_len > 0);
	}

}