04-01-2014
Quote:
Originally Posted by
DGPickett
You did not say how much RAM you have, which is a definite factor.
The MD5 result is impressive. Is MD5 as cheap as a good hash? Perhaps CPUs have gotten so much faster than disk that it is not a factor!
In perl/C/C++/JAVA you can mmap the input file both for input and so your hash map can hold a 64 bit char* for exact verification, reducing copying and space allocation overhead.
The exact verification seems to expand the vm footprint a lot, but the most likely case is that the md5 or hash is new and so the exact compare is not done, greatly reducing processing and the vm footprint with a small minority of duplicates. If there were a lot of duplicates, that hurts the VM footprint with more exact verifications, but conversely there is less final data in the map.
I have 16 GB of ram but my "disks" are also solid state. It's a fast system. The md5 solution is working well for me.
Mike
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md5(3) OpenSSL md5(3)
NAME
MD2, MD4, MD5, MD2_Init, MD2_Update, MD2_Final, MD4_Init, MD4_Update, MD4_Final, MD5_Init, MD5_Update, MD5_Final - MD2, MD4, and MD5 hash
functions
SYNOPSIS
#include <openssl/md2.h>
unsigned char *MD2(const unsigned char *d, unsigned long n,
unsigned char *md);
void MD2_Init(MD2_CTX *c);
void MD2_Update(MD2_CTX *c, const unsigned char *data,
unsigned long len);
void MD2_Final(unsigned char *md, MD2_CTX *c);
#include <openssl/md4.h>
unsigned char *MD4(const unsigned char *d, unsigned long n,
unsigned char *md);
void MD4_Init(MD4_CTX *c);
void MD4_Update(MD4_CTX *c, const void *data,
unsigned long len);
void MD4_Final(unsigned char *md, MD4_CTX *c);
#include <openssl/md5.h>
unsigned char *MD5(const unsigned char *d, unsigned long n,
unsigned char *md);
void MD5_Init(MD5_CTX *c);
void MD5_Update(MD5_CTX *c, const void *data,
unsigned long len);
void MD5_Final(unsigned char *md, MD5_CTX *c);
DESCRIPTION
MD2, MD4, and MD5 are cryptographic hash functions with a 128 bit output.
MD2(), MD4(), and MD5() compute the MD2, MD4, and MD5 message digest of the n bytes at d and place it in md (which must have space for
MD2_DIGEST_LENGTH == MD4_DIGEST_LENGTH == MD5_DIGEST_LENGTH == 16 bytes of output). If md is NULL, the digest is placed in a static array.
The following functions may be used if the message is not completely stored in memory:
MD2_Init() initializes a MD2_CTX structure.
MD2_Update() can be called repeatedly with chunks of the message to be hashed (len bytes at data).
MD2_Final() places the message digest in md, which must have space for MD2_DIGEST_LENGTH == 16 bytes of output, and erases the MD2_CTX.
MD4_Init(), MD4_Update(), MD4_Final(), MD5_Init(), MD5_Update(), and MD5_Final() are analogous using an MD4_CTX and MD5_CTX structure.
Applications should use the higher level functions EVP_DigestInit(3) etc. instead of calling the hash functions directly.
NOTE
MD2, MD4, and MD5 are recommended only for compatibility with existing applications. In new applications, SHA-1 or RIPEMD-160 should be
preferred.
RETURN VALUES
MD2(), MD4(), and MD5() return pointers to the hash value.
MD2_Init(), MD2_Update(), MD2_Final(), MD4_Init(), MD4_Update(), MD4_Final(), MD5_Init(), MD5_Update(), and MD5_Final() do not return val-
ues.
CONFORMING TO
RFC 1319, RFC 1320, RFC 1321
SEE ALSO
sha(3), ripemd(3), EVP_DigestInit(3)
HISTORY
MD2(), MD2_Init(), MD2_Update() MD2_Final(), MD5(), MD5_Init(), MD5_Update() and MD5_Final() are available in all versions of SSLeay and
OpenSSL.
MD4(), MD4_Init(), and MD4_Update() are available in OpenSSL 0.9.6 and above.
0.9.7a 2000-08-14 md5(3)