// per table B.3.
	zigStart, zigEnd, ah, al := int32(0), int32(blockSize-1), uint32(0), uint32(0)
	if d.progressive {
		zigStart = int32(d.tmp[1+2*nComp])
		zigEnd = int32(d.tmp[2+2*nComp])
		ah = uint32(d.tmp[3+2*nComp] >> 4)
		al = uint32(d.tmp[3+2*nComp] & 0x0f)
		if (zigStart == 0 && zigEnd != 0) || zigStart > zigEnd || blockSize <= zigEnd {
			return FormatError("bad spectral selection bounds")
		}

//     [31:31] (offset 31, bit count 1) and the register is W for 0 and X for 1.
//
// - arg_[s|u]label_FIELDS_POWER:
//     a program label encoded as "FIELDS" times 2^POWER in the range [MIN, MAX] (determined
//     by signd/unsigned, FIELDS and POWER), e.g.
//       arg_slabel_imm14_2
//       arg_slabel_imm19_2
//       arg_slabel_imm26_2
//       arg_slabel_immhi_immlo_0
//       arg_slabel_immhi_immlo_12
//