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Zlib

Why

Provides compression and decompression via the system zlib library. Supports Raw deflate, Zlib, and Gzip formats in both streaming and one-shot modes. Caller provides all buffers, so there is no hidden allocation on the Modula-2 side. Requires -lz at link time.

Types

  • Stream (ADDRESS) -- Opaque zlib stream handle.
  • Status -- Ok, StreamEnd, NeedMore, Error.
  • Level -- NoCompression, BestSpeed, Default, BestCompression.
  • Format -- Raw, ZlibFmt, Gzip.

Procedures

Streaming Compression

  • PROCEDURE DeflateInit(VAR s: Stream; level: Level; fmt: Format): Status Initialise a compression stream.

  • PROCEDURE Deflate(VAR s: Stream; src: ADDRESS; srcLen: CARDINAL; dst: ADDRESS; dstMax: CARDINAL; VAR produced: CARDINAL; flush: BOOLEAN): Status Compress from src into dst. Set flush to TRUE to finalise the stream. produced is set to the number of bytes written to dst.

  • PROCEDURE DeflateEnd(VAR s: Stream): Status Free compression stream resources.

Streaming Decompression

  • PROCEDURE InflateInit(VAR s: Stream; fmt: Format): Status Initialise a decompression stream.

  • PROCEDURE Inflate(VAR s: Stream; src: ADDRESS; srcLen: CARDINAL; dst: ADDRESS; dstMax: CARDINAL; VAR produced: CARDINAL): Status Decompress from src into dst. produced is set to the number of bytes written to dst.

  • PROCEDURE InflateEnd(VAR s: Stream): Status Free decompression stream resources.

One-Shot Convenience

  • PROCEDURE Compress(src: ADDRESS; srcLen: CARDINAL; dst: ADDRESS; dstMax: CARDINAL; VAR dstLen: CARDINAL; fmt: Format): Status Compress an entire buffer in one call.

  • PROCEDURE Decompress(src: ADDRESS; srcLen: CARDINAL; dst: ADDRESS; dstMax: CARDINAL; VAR dstLen: CARDINAL; fmt: Format): Status Decompress an entire buffer in one call.

Example

MODULE ZlibDemo;

FROM SYSTEM IMPORT ADR;
FROM InOut IMPORT WriteString, WriteLn, WriteCard;
FROM Zlib IMPORT Status, Level, Format, Ok, Default, Gzip,
                 Compress, Decompress;

VAR
  src: ARRAY [0..63] OF CHAR;
  compressed: ARRAY [0..255] OF CHAR;
  decompressed: ARRAY [0..255] OF CHAR;
  compLen, decompLen: CARDINAL;
  s: Status;

BEGIN
  src := "Hello, compressed world!";

  s := Compress(ADR(src), 24, ADR(compressed), 256, compLen, Gzip);
  IF s = Ok THEN
    WriteString("compressed to ");
    WriteCard(compLen, 0);
    WriteString(" bytes"); WriteLn;

    s := Decompress(ADR(compressed), compLen,
                    ADR(decompressed), 256, decompLen, Gzip);
    IF s = Ok THEN
      WriteString(decompressed); WriteLn
    END
  END
END ZlibDemo.