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WebSVN – planix.SVN – Blame – /os/branches/feature_fixcpp/sys/src/cmd/venti/srv/fmtbloom.c – Rev 2

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#include "stdinc.h"
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#include "dat.h"
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#include "fns.h"
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Bloom b;
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void
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usage(void)
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{
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	fprint(2, "usage: fmtbloom [-s size] [-n nblocks | -N nhash] file\n");
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	threadexitsall(0);
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}
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void
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threadmain(int argc, char *argv[])
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{
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	Part *part;
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	char *file;
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	vlong bits, size, size2;
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	int nhash;
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	vlong nblocks;
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	ventifmtinstall();
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	statsinit();
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	size = 0;
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	nhash = 0;
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	nblocks = 0;
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	ARGBEGIN{
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	case 'n':
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		if(nhash || nblocks)
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			usage();
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		nblocks = unittoull(EARGF(usage()));
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		break;
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	case 'N':
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		if(nhash || nblocks)
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			usage();
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		nhash = unittoull(EARGF(usage()));
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		if(nhash > BloomMaxHash){
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			fprint(2, "maximum possible is -N %d", BloomMaxHash);
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			usage();
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		}
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		break;
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	case 's':
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		size = unittoull(ARGF());
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		if(size == ~0)
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			usage();
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		break;
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	default:
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		usage();
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		break;
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	}ARGEND
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	if(argc != 1)
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		usage();
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	file = argv[0];
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	part = initpart(file, ORDWR|ODIRECT);
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	if(part == nil)
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		sysfatal("can't open partition %s: %r", file);
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	if(size == 0)
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		size = part->size;
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	if(size < 1024*1024)
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		sysfatal("bloom filter too small");
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	if(size > MaxBloomSize){
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		fprint(2, "warning: not using entire %,lld bytes; using only %,lld bytes\n",
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			size, (vlong)MaxBloomSize);
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		size = MaxBloomSize;
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	}
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	if(size&(size-1)){
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		for(size2=1; size2<size; size2*=2)
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			;
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		size = size2/2;
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		fprint(2, "warning: size not a power of 2; only using %lldMB\n", size/1024/1024);
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	}
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	if(nblocks){
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		/*
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		 * no use for more than 32 bits per block
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		 * shoot for less than 64 bits per block
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		 */
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		size2 = size;
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		while(size2*8 >= nblocks*64)
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			size2 >>= 1;
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		if(size2 != size){
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			size = size2;
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			fprint(2, "warning: using only %lldMB - not enough blocks to warrant more\n",
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				size/1024/1024);
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		}
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		/*
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		 * optimal is to use ln 2 times as many hash functions as we have bits per blocks.
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		 */
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		bits = (8*size)/nblocks;
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		nhash = bits*7/10;
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		if(nhash > BloomMaxHash)
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			nhash = BloomMaxHash;
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	}
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	if(!nhash)
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		nhash = BloomMaxHash;
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	if(bloominit(&b, size, nil) < 0)
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		sysfatal("bloominit: %r");
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	b.nhash = nhash;
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	bits = nhash*10/7;
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	nblocks = (8*size)/bits;
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	fprint(2, "fmtbloom: using %lldMB, %d hashes/score, best up to %,lld blocks\n", size/1024/1024, nhash, nblocks);
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	b.data = vtmallocz(size);
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	b.part = part;
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	if(writebloom(&b) < 0)
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		sysfatal("writing %s: %r", file);
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	threadexitsall(0);
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}