Reading RECT from SWF file

gistfile1.txt

/* read signed bit */
/* flush = YES to clear remaining bits */
uint8 readSB(FILE *file, BOOL flush)
{
    static uint8 bits = 0;
    static uint8 bitpos = 8;
    
    if (bitpos > 7) {
        bits = readUI8(file);
        bitpos = 0;
    }
    
    if (flush) {
        bitpos = 8;
        return 0;
    }
    
    return (bits >> (7 - bitpos++)) & 0x01;
}

CGRect readRECT(FILE *file)
{   
    int nbits = readSB(file, NO) << 4 |
                readSB(file, NO) << 3 |
                readSB(file, NO) << 2 |
                readSB(file, NO) << 1 |
                readSB(file, NO);
    
    uint64 Xmin = 0, Xmax = 0, Ymin = 0, Ymax = 0;
    for (int bit = nbits; bit > 0; ) { Xmin |= readSB(file, NO) << --bit; }
    for (int bit = nbits; bit > 0; ) { Xmax |= readSB(file, NO) << --bit; }
    for (int bit = nbits; bit > 0; ) { Ymin |= readSB(file, NO) << --bit; }
    for (int bit = nbits; bit > 0; ) { Ymax |= readSB(file, NO) << --bit; }
    
    readSB(NULL, YES);
    return CGRectMake(Xmin, Ymin, Xmax, Ymax);
}