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/*
* Copyright (c) 2017-2020, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under both the BSD-style license (found in the
* LICENSE file in the root directory of this source tree) and the GPLv2 (found
* in the COPYING file in the root directory of this source tree).
* You may select, at your option, one of the above-listed licenses.
*/
#include "seqgen.h"
#include "mem.h"
#include <string.h>
#define MIN(a, b) ((a) < (b) ? (a) : (b))
static const size_t kMatchBytes = 128;
#define SEQ_rotl32(x,r) ((x << r) | (x >> (32 - r)))
static BYTE SEQ_randByte(unsigned* src)
{
static const U32 prime1 = 2654435761U;
static const U32 prime2 = 2246822519U;
U32 rand32 = *src;
rand32 *= prime1;
rand32 ^= prime2;
rand32 = SEQ_rotl32(rand32, 13);
*src = rand32;
return (BYTE)(rand32 >> 5);
}
SEQ_stream SEQ_initStream(unsigned seed)
{
SEQ_stream stream;
stream.state = 0;
XXH64_reset(&stream.xxh, 0);
stream.seed = seed;
return stream;
}
/* Generates a single guard byte, then match length + 1 of a different byte,
* then another guard byte.
*/
static size_t SEQ_gen_matchLength(SEQ_stream* stream, unsigned value,
SEQ_outBuffer* out)
{
typedef enum {
ml_first_byte = 0,
ml_match_bytes,
ml_last_byte,
} ml_state;
BYTE* const ostart = (BYTE*)out->dst;
BYTE* const oend = ostart + out->size;
BYTE* op = ostart + out->pos;
switch ((ml_state)stream->state) {
case ml_first_byte:
/* Generate a single byte and pick a different byte for the match */
if (op >= oend) {
stream->bytesLeft = 1;
break;
}
*op = SEQ_randByte(&stream->seed) & 0xFF;
do {
stream->saved = SEQ_randByte(&stream->seed) & 0xFF;
} while (*op == stream->saved);
++op;
/* State transition */
stream->state = ml_match_bytes;
stream->bytesLeft = value + 1;
/* fall-through */
case ml_match_bytes: {
/* Copy matchLength + 1 bytes to the output buffer */
size_t const setLength = MIN(stream->bytesLeft, (size_t)(oend - op));
if (setLength > 0) {
memset(op, stream->saved, setLength);
op += setLength;
stream->bytesLeft -= setLength;
}
if (stream->bytesLeft > 0)
break;
/* State transition */
stream->state = ml_last_byte;
}
/* fall-through */
case ml_last_byte:
/* Generate a single byte and pick a different byte for the match */
if (op >= oend) {
stream->bytesLeft = 1;
break;
}
do {
*op = SEQ_randByte(&stream->seed) & 0xFF;
} while (*op == stream->saved);
++op;
/* State transition */
/* fall-through */
default:
stream->state = 0;
stream->bytesLeft = 0;
break;
}
XXH64_update(&stream->xxh, ostart + out->pos, (op - ostart) - out->pos);
out->pos = op - ostart;
return stream->bytesLeft;
}
/* Saves the current seed then generates kMatchBytes random bytes >= 128.
* Generates literal length - kMatchBytes random bytes < 128.
* Generates another kMatchBytes using the saved seed to generate a match.
* This way the match is easy to find for the compressors.
*/
static size_t SEQ_gen_litLength(SEQ_stream* stream, unsigned value, SEQ_outBuffer* out)
{
typedef enum {
ll_start = 0,
ll_run_bytes,
ll_literals,
ll_run_match,
} ll_state;
BYTE* const ostart = (BYTE*)out->dst;
BYTE* const oend = ostart + out->size;
BYTE* op = ostart + out->pos;
switch ((ll_state)stream->state) {
case ll_start:
stream->state = ll_run_bytes;
stream->saved = stream->seed;
stream->bytesLeft = MIN(kMatchBytes, value);
/* fall-through */
case ll_run_bytes:
while (stream->bytesLeft > 0 && op < oend) {
*op++ = SEQ_randByte(&stream->seed) | 0x80;
--stream->bytesLeft;
}
if (stream->bytesLeft > 0)
break;
/* State transition */
stream->state = ll_literals;
stream->bytesLeft = value - MIN(kMatchBytes, value);
/* fall-through */
case ll_literals:
while (stream->bytesLeft > 0 && op < oend) {
*op++ = SEQ_randByte(&stream->seed) & 0x7F;
--stream->bytesLeft;
}
if (stream->bytesLeft > 0)
break;
/* State transition */
stream->state = ll_run_match;
stream->bytesLeft = MIN(kMatchBytes, value);
/* fall-through */
case ll_run_match: {
while (stream->bytesLeft > 0 && op < oend) {
*op++ = SEQ_randByte(&stream->saved) | 0x80;
--stream->bytesLeft;
}
if (stream->bytesLeft > 0)
break;
}
/* fall-through */
default:
stream->state = 0;
stream->bytesLeft = 0;
break;
}
XXH64_update(&stream->xxh, ostart + out->pos, (op - ostart) - out->pos);
out->pos = op - ostart;
return stream->bytesLeft;
}
/* Saves the current seed then generates kMatchBytes random bytes >= 128.
* Generates offset - kMatchBytes of zeros to get a large offset without
* polluting the hash tables.
* Generates another kMatchBytes using the saved seed to generate a with the
* required offset.
*/
static size_t SEQ_gen_offset(SEQ_stream* stream, unsigned value, SEQ_outBuffer* out)
{
typedef enum {
of_start = 0,
of_run_bytes,
of_offset,
of_run_match,
} of_state;
BYTE* const ostart = (BYTE*)out->dst;
BYTE* const oend = ostart + out->size;
BYTE* op = ostart + out->pos;
switch ((of_state)stream->state) {
case of_start:
stream->state = of_run_bytes;
stream->saved = stream->seed;
stream->bytesLeft = MIN(value, kMatchBytes);
/* fall-through */
case of_run_bytes: {
while (stream->bytesLeft > 0 && op < oend) {
*op++ = SEQ_randByte(&stream->seed) | 0x80;
--stream->bytesLeft;
}
if (stream->bytesLeft > 0)
break;
/* State transition */
stream->state = of_offset;
stream->bytesLeft = value - MIN(value, kMatchBytes);
}
/* fall-through */
case of_offset: {
/* Copy matchLength + 1 bytes to the output buffer */
size_t const setLength = MIN(stream->bytesLeft, (size_t)(oend - op));
if (setLength > 0) {
memset(op, 0, setLength);
op += setLength;
stream->bytesLeft -= setLength;
}
if (stream->bytesLeft > 0)
break;
/* State transition */
stream->state = of_run_match;
stream->bytesLeft = MIN(value, kMatchBytes);
}
/* fall-through */
case of_run_match: {
while (stream->bytesLeft > 0 && op < oend) {
*op++ = SEQ_randByte(&stream->saved) | 0x80;
--stream->bytesLeft;
}
if (stream->bytesLeft > 0)
break;
}
/* fall-through */
default:
stream->state = 0;
stream->bytesLeft = 0;
break;
}
XXH64_update(&stream->xxh, ostart + out->pos, (op - ostart) - out->pos);
out->pos = op - ostart;
return stream->bytesLeft;
}
/* Returns the number of bytes left to generate.
* Must pass the same type/value until it returns 0.
*/
size_t SEQ_gen(SEQ_stream* stream, SEQ_gen_type type, unsigned value, SEQ_outBuffer* out)
{
switch (type) {
case SEQ_gen_ml: return SEQ_gen_matchLength(stream, value, out);
case SEQ_gen_ll: return SEQ_gen_litLength(stream, value, out);
case SEQ_gen_of: return SEQ_gen_offset(stream, value, out);
case SEQ_gen_max: /* fall-through */
default: return 0;
}
}
/* Returns the xxhash of the data produced so far */
XXH64_hash_t SEQ_digest(SEQ_stream const* stream)
{
return XXH64_digest(&stream->xxh);
}
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