def target_from_bits(bits)
      exponent = ((bits >> 24) & 0xff)
      mantissa = bits & 0x7fffff
      mantissa *= -1 if (bits & 0x800000) > 0
      (mantissa * (256**(exponent-3))).to_i
    end
def target_from_bits(bits)
      exponent = ((bits >> 24) & 0xff)
      mantissa = bits & 0x7fffff
      mantissa *= -1 if (bits & 0x800000) > 0
      (mantissa * (256**(exponent-3))).to_i
    end
Converts 32-bit compact representation to a 256-bit integer.
 int32 -> bigint