bgzf.py 文件源码

def _write_block(self, block):
        # print("Saving %i bytes" % len(block))
        assert len(block) <= 65536
        # Giving a negative window bits means no gzip/zlib headers,
        # -15 used in samtools
        c = zlib.compressobj(self.compresslevel,
                             zlib.DEFLATED,
                             -15,
                             zlib.DEF_MEM_LEVEL,
                             0)
        compressed = c.compress(block) + c.flush()
        del c
        assert len(compressed) < 65536, \
            "TODO - Didn't compress enough, try less data in this block"
        crc = zlib.crc32(block)
        # Should cope with a mix of Python platforms...
        if crc < 0:
            crc = struct.pack("<i", crc)
        else:
            crc = struct.pack("<I", crc)
        bsize = struct.pack("<H", len(compressed) + 25)  # includes -1
        crc = struct.pack("<I", zlib.crc32(block) & 0xffffffff)
        uncompressed_length = struct.pack("<I", len(block))
        # Fixed 16 bytes,
        # gzip magic bytes (4) mod time (4),
        # gzip flag (1), os (1), extra length which is six (2),
        # sub field which is BC (2), sub field length of two (2),
        # Variable data,
        # 2 bytes: block length as BC sub field (2)
        # X bytes: the data
        # 8 bytes: crc (4), uncompressed data length (4)
        data = _bgzf_header + bsize + compressed + crc + uncompressed_length
        self._handle.write(data)