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slightly improved hash values

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This commit is contained in:
Darren Ranalli 2004-05-27 00:14:27 +00:00
parent d0acfcc4ac
commit 798348ea12
2 changed files with 9 additions and 3 deletions
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11
panda/src/express/patchfile.cxx
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@ -94,11 +94,12 @@ const PN_uint32 Patchfile::_magic_number = 0xfeebfaac;
// To version 2 on 11/2/02 to store copy offsets as relative.
const PN_uint16 Patchfile::_current_version = 2;
const PN_uint32 Patchfile::_HASHTABLESIZE = PN_uint32(1) << 24;
const PN_uint32 Patchfile::_HASH_BITS = 24;
const PN_uint32 Patchfile::_HASHTABLESIZE = PN_uint32(1) << Patchfile::_HASH_BITS;
const PN_uint32 Patchfile::_DEFAULT_FOOTPRINT_LENGTH = 9; // this produced the smallest patch file for libpanda.dll when tested, 12/20/2000
const PN_uint32 Patchfile::_NULL_VALUE = PN_uint32(0) - 1;
const PN_uint32 Patchfile::_MAX_RUN_LENGTH = (PN_uint32(1) << 16) - 1;
const PN_uint32 Patchfile::_HASH_MASK = (PN_uint32(1) << 24) - 1;
const PN_uint32 Patchfile::_HASH_MASK = (PN_uint32(1) << Patchfile::_HASH_BITS) - 1;
////////////////////////////////////////////////////////////////////
// Function: Patchfile::Constructor
@ -543,10 +544,14 @@ calc_hash(const char *buffer) {
for(int i = 0; i < (int)_footprint_length; i++) {
// this is probably not such a good hash. to be replaced
/// --> TRIED MD5, was not worth it for the execution-time hit on 800Mhz PC
hash_value ^= (*buffer) << ((i % _footprint_length) * 2);
hash_value ^= PN_uint32(*buffer) << ((i * 2) % Patchfile::_HASH_BITS);
buffer++;
}
// use the bits that overflowed past the end of the hash bit range
// (this is intended for _HASH_BITS == 24)
hash_value ^= (hash_value >> Patchfile::_HASH_BITS);
//cout << hash_value << " ";
return hash_value & _HASH_MASK;

1
panda/src/express/patchfile.h
View File

@ -96,6 +96,7 @@ private:
PN_uint32 COPY_pos, PN_uint32 last_copy_pos,
PN_uint32 ADD_pos);
static const PN_uint32 _HASH_BITS;
static const PN_uint32 _HASHTABLESIZE;
static const PN_uint32 _DEFAULT_FOOTPRINT_LENGTH;
static const PN_uint32 _NULL_VALUE;