The "de" decompression function must be provided the entire compressed block at
once as a byte data type vector (eg ⎕dr 4 80 83); it returns the decompressed
result as data of the same type.
If there is any decompression error, "de" returns a scalar negative 1.
⎕dr is used: (1) to convert byte data to binary (11 ⎕dr x); (2) to convert
decoded uncompressed bytes from binary to the output byte data type.
The "deh" function is used by "de" to build Huffman decoding tables.
The exact number of RFC-1950 bytes must be supplied or an error will occur
(this means the adler32 sum must be the last 4 bytes). The decompressor checks
that the last compressed bit is read from the byte preceding the adler32 sum --
this check can be disabled by modifying the "ad:" line.
By default the adler32 sum itself is NOT verified, since it makes the decompression
10x slower. The adler32 check may be enabled by removing the ",0" in the "ad:" line.
Note: there is extra logic to enlarge the output buffer in large chunks. Originally
raw bytes and copies were simply concatenated to existing output; however, this was
very slow (30x slower).
The ⎕wa needed to run will be approx. 16meg + 2× size of the decompressed output.
Decompress zlib RFC-1950 in APL2
[page last modified 2023-04-04]
This is APL2 code to decompress (inflate) a block of RFC-1950 (zlib) data. It was
originally written 3/13/2023 in Micro Apl APLX for Windows version 5.1.0.
As of 3/29/2023 it also runs in Dyalog Windows version 18.2.45405.0 64 Unicode.
r←de b;c;d;dt;e;f;ft;g;h;i;l;lt;n;o;p;t;u;x;⎕IO ⍝decompress RFC-1950. paulhoule.com 3/29/2023 o←x←ft←⎕IO←0 ⋄ t←⎕dr r←0⍴b ⋄ i←¯16+0⊃⍴b←11 ⎕dr⌽b u←t ⎕dr,1=⍉(8⍴2)⊤⍳256 ⋄ lt←256 1 8 21/rw bs cp cx →(c[2 8]∨(8≠2⊥¯4↑c)∨×31|2⊥8⌽c←¯16↑b)/er lt←lt,¯286 2↑(258⌊2++\2*c),[0.5]1⌽c←¯29↑4/⍳6 dt←(+\2*0,¯1↓c),[0.5]c←2/0,⍳14 ex:p←¯258+0⊃⍴r←(4096+⍴r)↑r bs:→x⍴ad ⋄ →(2⊥2↑(c d x)←b[(⍳3)+i←i-3])⊃nc fh dh er nc:→(≠/c←2⊥⍉1 0≠[0]2 16⍴b[(⍳32)+i←i-32+8|i])⍴er o←0⊃⍴r←(o⍴r),⌽t ⎕dr b[(⍳c)+i←i-c←8×0⊃c] ⋄ →ex fh:→(0≢(e g d f)←ft)⍴fa ⋄ c←144 112 24 8/8 9 7 8 ft←(1+⍳¨9 5),(⊂deh c),⊂(⍳32),[0.5]5 ⋄ →fh dh:→(286<n←257 1 4+⌽0 32 32⊤2⊥b[(⍳14)+i←i-14])/er e←16 17 18 0 8 7 9 6 10 5 11 4 12 3 13 2 14 1 15 f←0⍴d←(19↑⌽2⊥⍉d 3⍴b[(⍳c)+i←i-c←3×d←2⊃n])[⍋e] e←1+⍳⌈/d ⋄ →(¯1≡d←deh d)⍴er ⋄ (n g)←+\2⍴n hl:i←i-1⊃c←d[2⊥b[i-e];] ⋄ →(16>c←0⊃c)⍴h5 ⋄ c←c-16 c←((2⊥b[(⍳c)+i←i-c←c⊃2 3 7])+c⊃3 3 11)⍴1↑c↓¯1↑f h5:→(g>⍴f←f,c)⍴hl ⋄ →(g≠⍴f)⍴er ⋄ f←(n⍴f)(n↓f) ⍎(2>c←+/1⊃f)/'f[1]←⊂(1⊃f),c↓1 1 ⍝very rare' (e g)←1+⍳¨⌈/¨f ⋄ →(¯1∊(d f)←deh¨f)⊃fa er rw:r[o]←u[c] ⋄ →(p≥o←o+1)⍴fa ov:r←(258+p←p+16777216⌊p)↑r ⋄ →fa cx:l←l+2⊥b[(⍳n)+i←i-n] cp:(c n)←f[2⊥b[i-g];] i←i-n ⋄ (c n)←dt[c;] ⋄ c←c+2⊥b[(⍳n)+i←i-n] r[o+⍳l]←l⍴r[(o-c)+⍳c⌊l] ⋄ →(p<o←o+l)⍴ov fa:(c n)←d[2⊥b[i-e];] ⋄ i←i-n ⋄ →(h l n)←lt[c;] ad:r←o⍴r ⋄ →(i∊32+⍳8)↓er,0 ⋄ c←1,i←0 ⋄ →o↓ax an:c←65521|+\c+2↑2⊥11 ⎕dr i⊃r ⋄ →(o≠i←i+1)⍴an ax:→er×(2⊥,⊖4 8⍴b)≠65536⊥⌽c er:r←¯1 r←deh b;c;d;e;f;i;l;n;⎕IO ⍝r←(n,2) huffman decoding table, or ¯1 if error ⍝b: bit length (0..15) per code; 0= code unused l←b~c←⎕IO←0 ⋄ r←¯1 ⋄ →⍳(1⌈⍴l)≠+/f←+⌿l∘.=1+⍳15 →⍳(f+.×15↑2*⌽⍳l)≠d←2*l←⌈/l ⋄ r←d 2⍴0 ⋄ d←(×f)/⍳⍴f nx:e←2*l-i←1+n←0⊃d ⋄ c←2⊥i↑c ⋄ n←n⊃f r[(⍳e)∘.+e×c+⍳n;]←e n 2⍴((b=i)/⍳⍴b),[0.5]i c←(i⍴2)⊤c+n ⋄ →(⍴d←1↓d)⍴nx
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