nrv2b.c

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// 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..

#ifndef ENDIAN
#define ENDIAN   0
#endif
#ifndef BITSIZE
#define BITSIZE 32
#endif

#define GETBIT_8(bb, src, ilen) \
    (((bb = bb & 0x7f ? bb*2 : ((unsigned)src[ilen++]*2+1)) >> 8) & 1)

#define GETBIT_LE16(bb, src, ilen) \
    (bb*=2,bb&0xffff ? (bb>>16)&1 : (ilen+=2,((bb=(src[ilen-2]+src[ilen-1]*256u)*2+1)>>16)&1))
#define GETBIT_LE32(bb, src, ilen) \
    (bc > 0 ? ((bb>>--bc)&1) : (bc=31,\
    bb=*(const uint32_t *)((src)+ilen),ilen+=4,(bb>>31)&1))

#if ENDIAN == 0 && BITSIZE == 8
#define GETBIT(bb, src, ilen) GETBIT_8(bb, src, ilen)
#endif
#if ENDIAN == 0 && BITSIZE == 16
#define GETBIT(bb, src, ilen) GETBIT_LE16(bb, src, ilen)
#endif
#if ENDIAN == 0 && BITSIZE == 32
#define GETBIT(bb, src, ilen) GETBIT_LE32(bb, src, ilen)
#endif
static unsigned long unrv2b(uint8_t * src, uint8_t * dst, unsigned long *ilen_p)
{
        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;
        /* FIXME: check olen with the length stored in first 4 bytes */ 

        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);
        }

        *ilen_p = ilen;

        return olen;

}