[Libre-soc-isa] [Bug 933] New: prefix-code (like huffman code) decode/encode instructions

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Wed Sep 21 21:53:48 BST 2022


            Bug ID: 933
           Summary: prefix-code (like huffman code) decode/encode
           Product: Libre-SOC's first SoC
           Version: unspecified
          Hardware: PC
               URL: https://libre-soc.org/openpower/prefix_codes/
                OS: Linux
            Status: IN_PROGRESS
          Severity: enhancement
          Priority: ---
         Component: Specification
          Assignee: programmerjake at gmail.com
          Reporter: programmerjake at gmail.com
                CC: libre-soc-isa at lists.libre-soc.org
            Blocks: 222
   NLnet milestone: ---

While working on the JPEG decode/encode, I realized that we'll want
instructions to accelerate encoding/decoding huffman codes for jpeg, deflate
(gzip, zip, png, etc.), mp3, etc.

I am writing instructions to handle all prefix codes (more than just huffman
codes), decoding codes that are <=6-bit, longer codes are assumed to be less
common so can take a slow path (decode instruction sets overflow to signal a
>6-bit code).

WIP initial draft here:

so far I have the pseudo-code for an encode instruction, it encodes 1 or up to
8 codes. the huffman-style tree is encoded in an input 64-bit register.

Referenced Bugs:

[Bug 222] JPEG optimizations
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