diff options
Diffstat (limited to 'src/libflate/adler.c')
-rw-r--r-- | src/libflate/adler.c | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/src/libflate/adler.c b/src/libflate/adler.c new file mode 100644 index 00000000..22fb8f6d --- /dev/null +++ b/src/libflate/adler.c @@ -0,0 +1,72 @@ +#include <u.h> +#include <libc.h> +#include <flate.h> + +enum +{ + ADLERITERS = 5552, /* max iters before can overflow 32 bits */ + ADLERBASE = 65521 /* largest prime smaller than 65536 */ +}; + +ulong +adler32(ulong adler, void *vbuf, int n) +{ + ulong s1, s2; + uchar *buf, *ebuf; + int m; + + buf = vbuf; + s1 = adler & 0xffff; + s2 = (adler >> 16) & 0xffff; + for(; n >= 16; n -= m){ + m = n; + if(m > ADLERITERS) + m = ADLERITERS; + m &= ~15; + for(ebuf = buf + m; buf < ebuf; buf += 16){ + s1 += buf[0]; + s2 += s1; + s1 += buf[1]; + s2 += s1; + s1 += buf[2]; + s2 += s1; + s1 += buf[3]; + s2 += s1; + s1 += buf[4]; + s2 += s1; + s1 += buf[5]; + s2 += s1; + s1 += buf[6]; + s2 += s1; + s1 += buf[7]; + s2 += s1; + s1 += buf[8]; + s2 += s1; + s1 += buf[9]; + s2 += s1; + s1 += buf[10]; + s2 += s1; + s1 += buf[11]; + s2 += s1; + s1 += buf[12]; + s2 += s1; + s1 += buf[13]; + s2 += s1; + s1 += buf[14]; + s2 += s1; + s1 += buf[15]; + s2 += s1; + } + s1 %= ADLERBASE; + s2 %= ADLERBASE; + } + if(n){ + for(ebuf = buf + n; buf < ebuf; buf++){ + s1 += buf[0]; + s2 += s1; + } + s1 %= ADLERBASE; + s2 %= ADLERBASE; + } + return (s2 << 16) + s1; +} |