huff0: provide asm implementation of Decompress1X

[WojciechMula]

Decompress1X uses a similar approach to Decompress4X -- it first writes data to an auxiliary buffer, and the buffer is later appended to the output. In an asm we can write directly to the output (see: #577).

[WojciechMula]

@klauspost there is dead code: https://github.com/klauspost/compress/blob/master/huff0/decompress.go#L310. Should it be re-enabled?

[klauspost]

@WojciechMula Crashers happen after merge of #596 :(

Sample crashers.zip

Could you PTAL?

[klauspost]

Test is rather simple:

func FuzzDecompress(data []byte) int {
	s, rem, err := huff0.ReadTable(data, nil)
	if err != nil {
		return 0
	}
	_, err1 := s.Decompress1X(rem)
	_, err4 := s.Decompress4X(rem, huff0.BlockSizeMax-3)
	if err1 != nil && err4 != nil {
		return 0
	}
	return 1
} 

[klauspost]

unexpected fault address 0xffffffffffffffff
fatal error: fault
[signal 0xc0000005 code=0x0 addr=0xffffffffffffffff pc=0xa463ee]

goroutine 1 [running]:
runtime.throw({0xa62546, 0x22466b4ffff})
	runtime/panic.go:1198 +0x76 fp=0xc0000d3c48 sp=0xc0000d3c18 pc=0x9c3196
runtime.sigpanic()
	runtime/signal_windows.go:260 +0x10c fp=0xc0000d3c90 sp=0xc0000d3c48 pc=0x9d46ec
github.com/klauspost/compress/huff0.(*Scratch).compress1X(...)
	e:/gopath/src/github.com/klauspost/compress/huff0/compress.go:230
github.com/klauspost/compress/huff0.(*Scratch).compress1X-fm({0xc0000d3d40, 0x2246c27001b, 0xc0003e0000})
	e:/gopath/src/github.com/klauspost/compress/huff0/compress.go:229 +0x4e fp=0xc0000d3cd8 sp=0xc0000d3c90 pc=0xa463ee
github.com/klauspost/compress/huff0.(*Decoder).Decompress1X(0xc0000d3df0, {0xc0003a0000, 0x0, 0x4000000010}, {0x2246c27001b, 0x100, 0x0})
	e:/gopath/src/github.com/klauspost/compress/huff0/decompress_amd64.go:202 +0x1fd fp=0xc0000d3db0 sp=0xc0000d3cd8 pc=0xa444dd
github.com/klauspost/compress/huff0.(*Scratch).Decompress1X(0xc000315800, {0x2246c27001b, 0x1ccc8, 0x1ccc8})
	e:/gopath/src/github.com/klauspost/compress/huff0/decompress.go:189 +0x226 fp=0xc0000d3e40 sp=0xc0000d3db0 pc=0xa3f606
github.com/klauspost/compress-fuzz/huff0.FuzzDecompress({0x2246c270000, 0xc0000d3f08, 0xb0ea20})
	e:/gopath/src/github.com/klauspost/compress-fuzz/huff0/fuzz_decompress.go:10 +0x94 fp=0xc0000d3ea0 sp=0xc0000d3e40 pc=0xa47cf4
go-fuzz-dep.Main({0xc0000d3f60, 0x2, 0x9a6b45})
	go-fuzz-dep/main.go:36 +0x15b fp=0xc0000d3f48 sp=0xc0000d3ea0 pc=0x9fdc1b
main.main()
	github.com/klauspost/compress-fuzz/huff0/go.fuzz.main/main.go:17 +0x45 fp=0xc0000d3f80 sp=0xc0000d3f48 pc=0xa47e45
runtime.main()
	runtime/proc.go:255 +0x217 fp=0xc0000d3fe0 sp=0xc0000d3f80 pc=0x9c5757
runtime.goexit()
	runtime/asm_amd64.s:1581 +0x1 fp=0xc0000d3fe8 sp=0xc0000d3fe0 pc=0x9ec8a1
exit status 2

[klauspost]

@WojciechMula Please confirm that you are looking at this, otherwise I will have to revert.

[WojciechMula]

@klauspost I will take a look on Thursday. Please revert if it blocks anything, I'll back with a fix.

[klauspost]

No worries. Just don't want releases to be blocked if an urgent issue should come in.

[klauspost]

Released