/* RetroArch - A frontend for libretro.
* Copyright (C) 2010-2014 - Hans-Kristian Arntzen
* Copyright (C) 2014 - Alfred Agrell
*
* RetroArch 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 Found-
* ation, either version 3 of the License, or (at your option) any later version.
*
* RetroArch 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 RetroArch.
* If not, see <http://www.gnu.org/licenses/>.
*/
#define __STDC_LIMIT_MACROS
#include "rewind.h"
#include "performance.h"
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#ifndef UINT16_MAX
#define UINT16_MAX 0xffff
#endif
#ifndef UINT32_MAX
#define UINT32_MAX 0xffffffffu
#endif
#undef CPU_X86
#if defined(__x86_64__) || defined(__i386__) || defined(__i486__) || defined(__i686__)
#define CPU_X86
#endif
// Other arches SIGBUS (usually) on unaligned accesses.
#ifndef CPU_X86
#define NO_UNALIGNED_MEM
#endif
// Format per frame:
// size nextstart;
// repeat {
// uint16 numchanged; // everything is counted in units of uint16
// if (numchanged) {
// uint16 numunchanged; // skip these before handling numchanged
// uint16[numchanged] changeddata;
// }
// else
// {
// uint32 numunchanged;
// if (!numunchanged) break;
// }
// }
// size thisstart;
//
// The start offsets point to 'nextstart' of any given compressed frame.
// Each uint16 is stored native endian; anything that claims any other endianness refers to the endianness of this specific item.
// The uint32 is stored little endian.
// Each size value is stored native endian if alignment is not enforced; if it is, they're little endian.
// The start of the buffer contains a size pointing to the end of the buffer; the end points to its start.
// Wrapping is handled by returning to the start of the buffer if the compressed data could potentially hit the edge;
// if the compressed data could potentially overwrite the tail pointer, the tail retreats until it can no longer collide.
// This means that on average, ~2 * maxcompsize is unused at any given moment.
// These are called very few constant times per frame, keep it as simple as possible.
static inline void write_size_t(void *ptr, size_t val)
{
memcpy(ptr, &val, sizeof(val));
}
static inline size_t read_size_t(const void *ptr)
{
size_t ret;
memcpy(&ret, ptr, sizeof(ret));
return ret;
}
struct state_manager
{
uint8_t *data;
size_t capacity;
uint8_t *head; // Reading and writing is done here.
uint8_t *tail; // If head comes close to this, discard a frame.
uint8_t *thisblock;
uint8_t *nextblock;
size_t blocksize; // This one is runded up from reset::blocksize.
size_t maxcompsize; // size_t + (blocksize + 131071) / 131072 * (blocksize + u16 + u16) + u16 + u32 + size_t (yes, the math is a bit ugly).
unsigned entries;
bool thisblock_valid;
};
state_manager_t *state_manager_new(size_t state_size, size_t buffer_size)
{
state_manager_t *state = (state_manager_t*)calloc(1, sizeof(*state));
if (!state)
return NULL;
size_t newblocksize = ((state_size - 1) | (sizeof(uint16_t) - 1)) + 1;
state->blocksize = newblocksize;
const int maxcblkcover = UINT16_MAX * sizeof(uint16_t);
const int maxcblks = (state->blocksize + maxcblkcover - 1) / maxcblkcover;
state->maxcompsize = state->blocksize + maxcblks * sizeof(uint16_t) * 2 + sizeof(uint16_t) + sizeof(uint32_t) + sizeof(size_t) * 2;
state->data = (uint8_t*)malloc(buffer_size);
state->thisblock = (uint8_t*)calloc(state->blocksize + sizeof(uint16_t) * 4 + 16, 1);
state->nextblock = (uint8_t*)calloc(state->blocksize + sizeof(uint16_t) * 4 + 16, 1);
if (!state->data || !state->thisblock || !state->nextblock)
goto error;
// Force in a different byte at the end, so we don't need to check bounds in the innermost loop (it's expensive).
// There is also a large amount of data that's the same, to stop the other scan
// There is also some padding at the end. This is so we don't read outside the buffer end if we're reading in large blocks;
// it doesn't make any difference to us, but sacrificing 16 bytes to get Valgrind happy is worth it.
*(uint16_t*)(state->thisblock + state->blocksize + sizeof(uint16_t) * 3) = 0xFFFF;
*(uint16_t*)(state->nextblock + state->blocksize + sizeof(uint16_t) * 3) = 0x0000;
state->capacity = buffer_size;
state->head = state->data + sizeof(size_t);
state->tail = state->data + sizeof(size_t);
return state;
error:
state_manager_free(state);
return NULL;
}
void state_manager_free(state_manager_t *state)
{
free(state->data);
free(state->thisblock);
free(state->nextblock);
free(state);
}
bool state_manager_pop(state_manager_t *state, const void **data)
{
*data = NULL;
if (state->thisblock_valid)
{
state->thisblock_valid = false;
state->entries--;
*data = state->thisblock;
return true;
}
if (state->head == state->tail)
return false;
size_t start = read_size_t(state->head - sizeof(size_t));
state->head = state->data + start;
const uint8_t *compressed = state->data + start + sizeof(size_t);
uint8_t *out = state->thisblock;
// Begin decompression code
// out is the last pushed (or returned) state
const uint16_t *compressed16 = (const uint16_t*)compressed;
uint16_t *out16 = (uint16_t*)out;
for (;;)
{
uint16_t i;
uint16_t numchanged = *(compressed16++);
if (numchanged)
{
out16 += *compressed16++;
// We could do memcpy, but it seems that memcpy has a constant-per-call overhead that actually shows up.
// Our average size in here seems to be 8 or something.
// Therefore, we do something with lower overhead.
for (i = 0; i < numchanged; i++)
out16[i] = compressed16[i];
compressed16 += numchanged;
out16 += numchanged;
}
else
{
uint32_t numunchanged = compressed16[0] | (compressed16[1] << 16);
if (!numunchanged)
break;
compressed16 += 2;
out16 += numunchanged;
}
}
// End decompression code
state->entries--;
*data = state->thisblock;
return true;
}
void state_manager_push_where(state_manager_t *state, void **data)
{
// We need to ensure we have an uncompressed copy of the last pushed state, or we could
// end up applying a 'patch' to wrong savestate, and that'd blow up rather quickly.
if (!state->thisblock_valid)
{
const void *ignored;
if (state_manager_pop(state, &ignored))
{
state->thisblock_valid = true;
state->entries++;
}
}
*data = state->nextblock;
}
#if __SSE2__
#if defined(__GNUC__)
static inline int compat_ctz(unsigned x)
{
return __builtin_ctz(x);
}
#else
// Only checks at nibble granularity, because that's what we need.
static inline int compat_ctz(unsigned x)
{
if (x & 0x000f)
return 0;
if (x & 0x00f0)
return 4;
if (x & 0x0f00)
return 8;
if (x & 0xf000)
return 12;
return 16;
}
#endif
#include <emmintrin.h>
// There's no equivalent in libc, you'd think so ... std::mismatch exists, but it's not optimized at all. :(
static inline size_t find_change(const uint16_t *a, const uint16_t *b)
{
const __m128i *a128 = (const __m128i*)a;
const __m128i *b128 = (const __m128i*)b;
for (;;)
{
__m128i v0 = _mm_loadu_si128(a128);
__m128i v1 = _mm_loadu_si128(b128);
__m128i c = _mm_cmpeq_epi32(v0, v1);
uint32_t mask = _mm_movemask_epi8(c);
if (mask != 0xffff) // Something has changed, figure out where.
{
size_t ret = (((uint8_t*)a128 - (uint8_t*)a) | (compat_ctz(~mask))) >> 1;
return ret | (a[ret] == b[ret]);
}
a128++;
b128++;
}
}
#else
static inline size_t find_change(const uint16_t *a, const uint16_t *b)
{
const uint16_t *a_org = a;
#ifdef NO_UNALIGNED_MEM
while (((uintptr_t)a & (sizeof(size_t) - 1)) && *a == *b)
{
a++;
b++;
}
if (*a == *b)
#endif
{
const size_t *a_big = (const size_t*)a;
const size_t *b_big = (const size_t*)b;
while (*a_big == *b_big)
{
a_big++;
b_big++;
}
a = (const uint16_t*)a_big;
b = (const uint16_t*)b_big;
while (*a == *b)
{
a++;
b++;
}
}
return a - a_org;
}
#endif
static inline size_t find_same(const uint16_t *a, const uint16_t *b)
{
const uint16_t *a_org = a;
#ifdef NO_UNALIGNED_MEM
if (((uintptr_t)a & (sizeof(uint32_t) - 1)) && *a != *b)
{
a++;
b++;
}
if (*a != *b)
#endif
{
// With this, it's random whether two consecutive identical words are caught.
// Luckily, compression rate is the same for both cases, and three is always caught.
// (We prefer to miss two-word blocks, anyways; fewer iterations of the outer loop, as well as in the decompressor.)
const uint32_t *a_big = (const uint32_t*)a;
const uint32_t *b_big = (const uint32_t*)b;
while (*a_big != *b_big)
{
a_big++;
b_big++;
}
a = (const uint16_t*)a_big;
b = (const uint16_t*)b_big;
if (a != a_org && a[-1] == b[-1])
{
a--;
b--;
}
}
return a - a_org;
}
void state_manager_push_do(state_manager_t *state)
{
if (state->thisblock_valid)
{
if (state->capacity < sizeof(size_t) + state->maxcompsize)
return;
recheckcapacity:;
size_t headpos = state->head - state->data;
size_t tailpos = state->tail - state->data;
size_t remaining = (tailpos + state->capacity - sizeof(size_t) - headpos - 1) % state->capacity + 1;
if (remaining <= state->maxcompsize)
{
state->tail = state->data + read_size_t(state->tail);
state->entries--;
goto recheckcapacity;
}
RARCH_PERFORMANCE_INIT(gen_deltas);
RARCH_PERFORMANCE_START(gen_deltas);
const uint8_t *oldb = state->thisblock;
const uint8_t *newb = state->nextblock;
uint8_t *compressed = state->head + sizeof(size_t);
// Begin compression code; 'compressed' will point to the end of the compressed data (excluding the prev pointer).
const uint16_t *old16 = (const uint16_t*)oldb;
const uint16_t *new16 = (const uint16_t*)newb;
uint16_t *compressed16 = (uint16_t*)compressed;
size_t num16s = state->blocksize / sizeof(uint16_t);
while (num16s)
{
size_t i;
size_t skip = find_change(old16, new16);
if (skip >= num16s)
break;
old16 += skip;
new16 += skip;
num16s -= skip;
if (skip > UINT16_MAX)
{
if (skip > UINT32_MAX)
{
// This will make it scan the entire thing again, but it only hits on 8GB unchanged
// data anyways, and if you're doing that, you've got bigger problems.
skip = UINT32_MAX;
}
*compressed16++ = 0;
*compressed16++ = skip;
*compressed16++ = skip >> 16;
skip = 0;
continue;
}
size_t changed = find_same(old16, new16);
if (changed > UINT16_MAX)
changed = UINT16_MAX;
*compressed16++ = changed;
*compressed16++ = skip;
for (i = 0; i < changed; i++)
compressed16[i] = old16[i];
old16 += changed;
new16 += changed;
num16s -= changed;
compressed16 += changed;
}
compressed16[0] = 0;
compressed16[1] = 0;
compressed16[2] = 0;
compressed = (uint8_t*)(compressed16 + 3);
// End compression code.
if (compressed - state->data + state->maxcompsize > state->capacity)
{
compressed = state->data;
if (state->tail == state->data + sizeof(size_t))
state->tail = state->data + read_size_t(state->tail);
}
write_size_t(compressed, state->head-state->data);
compressed += sizeof(size_t);
write_size_t(state->head, compressed-state->data);
state->head = compressed;
RARCH_PERFORMANCE_STOP(gen_deltas);
}
else
state->thisblock_valid = true;
uint8_t *swap = state->thisblock;
state->thisblock = state->nextblock;
state->nextblock = swap;
state->entries++;
return;
}
void state_manager_capacity(state_manager_t *state, unsigned *entries, size_t *bytes, bool *full)
{
size_t headpos = state->head - state->data;
size_t tailpos = state->tail - state->data;
size_t remaining = (tailpos + state->capacity - sizeof(size_t) - headpos - 1) % state->capacity + 1;
if (entries)
*entries = state->entries;
if (bytes)
*bytes = state->capacity-remaining;
if (full)
*full = remaining <= state->maxcompsize * 2;
}