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/* xdelta 3 - delta compression tools and library
* Copyright (C) 2001, 2003, 2004, 2005, 2006, 2007. Joshua P. MacDonald
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#ifndef _XDELTA3_HASH_H_
#define _XDELTA3_HASH_H_
#if XD3_DEBUG
#define SMALL_HASH_DEBUG1(s,inp) \
usize_t debug_state; \
usize_t debug_hval = xd3_checksum_hash (& (s)->small_hash, \
xd3_scksum (&debug_state, (inp), (s)->smatcher.small_look))
#define SMALL_HASH_DEBUG2(s,inp) \
XD3_ASSERT (debug_hval == xd3_checksum_hash (& (s)->small_hash, \
xd3_scksum (&debug_state, (inp), (s)->smatcher.small_look)))
#else
#define SMALL_HASH_DEBUG1(s,inp)
#define SMALL_HASH_DEBUG2(s,inp)
#endif /* XD3_DEBUG */
/* This is a good hash multiplier for 32-bit LCGs: see "linear
* congruential generators of different sizes and good lattice
* structure" */
static const uint32_t hash_multiplier = 1597334677U;
/***********************************************************************
Permute stuff
***********************************************************************/
#if HASH_PERMUTE == 0
#define PERMUTE(x) (x)
#else
#define PERMUTE(x) (__single_hash[(uint32_t)x])
extern const uint16_t __single_hash[256];
#endif
/* Update the checksum state. */
#if ADLER_LARGE_CKSUM
inline uint32_t
xd3_large_cksum_update (uint32_t cksum,
const uint8_t *base,
usize_t look) {
uint32_t old_c = PERMUTE(base[0]);
uint32_t new_c = PERMUTE(base[look]);
uint32_t low = ((cksum & 0xffff) - old_c + new_c) & 0xffff;
uint32_t high = ((cksum >> 16) - (old_c * look) + low) & 0xffff;
return (high << 16) | low;
}
#else
/* TODO: revisit this topic */
#endif
#if UNALIGNED_OK
#define UNALIGNED_READ32(dest,src) (*(dest)) = (*(uint32_t*)(src))
#else
#define UNALIGNED_READ32(dest,src) memcpy((dest), (src), 4);
#endif
/* TODO: small cksum is hard-coded for 4 bytes (i.e., "look" is unused) */
static inline uint32_t
xd3_scksum (uint32_t *state,
const uint8_t *base,
const usize_t look)
{
UNALIGNED_READ32(state, base);
return (*state) * hash_multiplier;
}
static inline uint32_t
xd3_small_cksum_update (uint32_t *state,
const uint8_t *base,
usize_t look)
{
UNALIGNED_READ32(state, base+1);
return (*state) * hash_multiplier;
}
/***********************************************************************
Ctable stuff
***********************************************************************/
static inline usize_t
xd3_checksum_hash (const xd3_hash_cfg *cfg, const usize_t cksum)
{
return (cksum >> cfg->shift) ^ (cksum & cfg->mask);
}
/***********************************************************************
Cksum function
***********************************************************************/
#if ADLER_LARGE_CKSUM
static inline uint32_t
xd3_lcksum (const uint8_t *seg, const usize_t ln)
{
usize_t i = 0;
uint32_t low = 0;
uint32_t high = 0;
for (; i < ln; i += 1)
{
low += PERMUTE(*seg++);
high += low;
}
return ((high & 0xffff) << 16) | (low & 0xffff);
}
#else
static inline uint32_t
xd3_lcksum (const uint8_t *seg, const usize_t ln)
{
usize_t i, j;
uint32_t h = 0;
for (i = 0, j = ln - 1; i < ln; ++i, --j) {
h += PERMUTE(seg[i]) * hash_multiplier_powers[j];
}
return h;
}
#endif
#if XD3_ENCODER
static usize_t
xd3_size_log2 (usize_t slots)
{
int bits = 28; /* This should not be an unreasonable limit. */
int i;
for (i = 3; i <= bits; i += 1)
{
if (slots < (1U << i))
{
/* TODO: this is compaction=1 in checksum_test.cc and maybe should
* not be fixed at -1. */
bits = i - 1;
break;
}
}
return bits;
}
static void
xd3_size_hashtable (xd3_stream *stream,
usize_t slots,
xd3_hash_cfg *cfg)
{
int bits = xd3_size_log2 (slots);
/* TODO: there's a 32-bit assumption here */
cfg->size = (1 << bits);
cfg->mask = (cfg->size - 1);
cfg->shift = 32 - bits;
}
#endif
#endif
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