func()

in flexflate/inflate.go [311:407]

• 85 lines of code
• 22 McCabe index (conditional complexity)

func (f *decompressor) readHuffman() error {
	// HLIT[5], HDIST[5], HCLEN[4].
	for f.nb < 5+5+4 {
		if err := f.moreBits(); err != nil {
			return err
		}
	}
	nlit := int(f.b&0x1F) + 257
	if nlit > maxLit {
		return CorruptInputError(f.roffset)
	}
	f.b >>= 5
	ndist := int(f.b&0x1F) + 1
	// maxDist is 32, so ndist is always valid.
	f.b >>= 5
	nclen := int(f.b&0xF) + 4
	// numCodes is 19, so nclen is always valid.
	f.b >>= 4
	f.nb -= 5 + 5 + 4

	// (HCLEN+4)*3 bits: code lengths in the magic codeOrder order.
	for i := 0; i < nclen; i++ {
		for f.nb < 3 {
			if err := f.moreBits(); err != nil {
				return err
			}
		}
		f.codebits[codeOrder[i]] = int(f.b & 0x7)
		f.b >>= 3
		f.nb -= 3
	}
	for i := nclen; i < len(codeOrder); i++ {
		f.codebits[codeOrder[i]] = 0
	}
	if !f.h1.init(f.codebits[0:]) {
		return CorruptInputError(f.roffset)
	}

	// HLIT + 257 code lengths, HDIST + 1 code lengths,
	// using the code length Huffman code.
	for i, n := 0, nlit+ndist; i < n; {
		x, err := f.huffSym(&f.h1)
		if err != nil {
			return err
		}
		if x < 16 {
			// Actual length.
			f.bits[i] = x
			i++
			continue
		}
		// Repeat previous length or zero.
		var rep int
		var nb uint
		var b int
		switch x {
		default:
			return InternalError("unexpected length code")
		case 16:
			rep = 3
			nb = 2
			if i == 0 {
				return CorruptInputError(f.roffset)
			}
			b = f.bits[i-1]
		case 17:
			rep = 3
			nb = 3
			b = 0
		case 18:
			rep = 11
			nb = 7
			b = 0
		}
		for f.nb < nb {
			if err := f.moreBits(); err != nil {
				return err
			}
		}
		rep += int(f.b & uint32(1<<nb-1))
		f.b >>= nb
		f.nb -= nb
		if i+rep > n {
			return CorruptInputError(f.roffset)
		}
		for j := 0; j < rep; j++ {
			f.bits[i] = b
			i++
		}
	}

	if !f.h1.init(f.bits[0:nlit]) || !f.h2.init(f.bits[nlit:nlit+ndist]) {
		return CorruptInputError(f.roffset)
	}

	return nil
}