tdeflatezlib.c - plan9port - [fork] Plan 9 from user space
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       ---
       tdeflatezlib.c (1073B)
       ---
            1 #include <u.h>
            2 #include <libc.h>
            3 #include <flate.h>
            4 #include "zlib.h"
            5 
            6 typedef struct ZRead        ZRead;
            7 
            8 struct ZRead
            9 {
           10         ulong        adler;
           11         void        *rr;
           12         int        (*r)(void*, void*, int);
           13 };
           14 
           15 static int
           16 zlread(void *vzr, void *buf, int n)
           17 {
           18         ZRead *zr;
           19 
           20         zr = vzr;
           21         n = (*zr->r)(zr->rr, buf, n);
           22         if(n <= 0)
           23                 return n;
           24         zr->adler = adler32(zr->adler, buf, n);
           25         return n;
           26 }
           27 
           28 int
           29 deflatezlib(void *wr, int (*w)(void*, void*, int), void *rr, int (*r)(void*, void*, int), int level, int debug)
           30 {
           31         ZRead zr;
           32         uchar buf[4];
           33         int ok;
           34 
           35         buf[0] = ZlibDeflate | ZlibWin32k;
           36 
           37         /* bogus zlib encoding of compression level */
           38         buf[1] = ((level > 2) + (level > 5) + (level > 8)) << 6;
           39 
           40         /* header check field */
           41         buf[1] |= 31 - ((buf[0] << 8) | buf[1]) % 31;
           42         if((*w)(wr, buf, 2) != 2)
           43                 return FlateOutputFail;
           44 
           45         zr.rr = rr;
           46         zr.r = r;
           47         zr.adler = 1;
           48         ok = deflate(wr, w, &zr, zlread, level, debug);
           49         if(ok != FlateOk)
           50                 return ok;
           51 
           52         buf[0] = zr.adler >> 24;
           53         buf[1] = zr.adler >> 16;
           54         buf[2] = zr.adler >> 8;
           55         buf[3] = zr.adler;
           56         if((*w)(wr, buf, 4) != 4)
           57                 return FlateOutputFail;
           58 
           59         return FlateOk;
           60 }