godot/thirdparty/zstd/compress/zstd_cwksp.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 * 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.
 */

#ifndef ZSTD_CWKSP_H
#define ZSTD_CWKSP_H

/*-*************************************
*  Dependencies
***************************************/
#include "../common/allocations.h"  /* ZSTD_customMalloc, ZSTD_customFree */
#include "../common/zstd_internal.h"
#include "../common/portability_macros.h"

#if defined (__cplusplus)
extern "C" {
#endif

/*-*************************************
*  Constants
***************************************/

/* Since the workspace is effectively its own little malloc implementation /
 * arena, when we run under ASAN, we should similarly insert redzones between
 * each internal element of the workspace, so ASAN will catch overruns that
 * reach outside an object but that stay inside the workspace.
 *
 * This defines the size of that redzone.
 */
#ifndef ZSTD_CWKSP_ASAN_REDZONE_SIZE
#define ZSTD_CWKSP_ASAN_REDZONE_SIZE …
#endif


/* Set our tables and aligneds to align by 64 bytes */
#define ZSTD_CWKSP_ALIGNMENT_BYTES …

/*-*************************************
*  Structures
***************************************/
ZSTD_cwksp_alloc_phase_e;

/**
 * Used to describe whether the workspace is statically allocated (and will not
 * necessarily ever be freed), or if it's dynamically allocated and we can
 * expect a well-formed caller to free this.
 */
ZSTD_cwksp_static_alloc_e;

/**
 * Zstd fits all its internal datastructures into a single continuous buffer,
 * so that it only needs to perform a single OS allocation (or so that a buffer
 * can be provided to it and it can perform no allocations at all). This buffer
 * is called the workspace.
 *
 * Several optimizations complicate that process of allocating memory ranges
 * from this workspace for each internal datastructure:
 *
 * - These different internal datastructures have different setup requirements:
 *
 *   - The static objects need to be cleared once and can then be trivially
 *     reused for each compression.
 *
 *   - Various buffers don't need to be initialized at all--they are always
 *     written into before they're read.
 *
 *   - The matchstate tables have a unique requirement that they don't need
 *     their memory to be totally cleared, but they do need the memory to have
 *     some bound, i.e., a guarantee that all values in the memory they've been
 *     allocated is less than some maximum value (which is the starting value
 *     for the indices that they will then use for compression). When this
 *     guarantee is provided to them, they can use the memory without any setup
 *     work. When it can't, they have to clear the area.
 *
 * - These buffers also have different alignment requirements.
 *
 * - We would like to reuse the objects in the workspace for multiple
 *   compressions without having to perform any expensive reallocation or
 *   reinitialization work.
 *
 * - We would like to be able to efficiently reuse the workspace across
 *   multiple compressions **even when the compression parameters change** and
 *   we need to resize some of the objects (where possible).
 *
 * To attempt to manage this buffer, given these constraints, the ZSTD_cwksp
 * abstraction was created. It works as follows:
 *
 * Workspace Layout:
 *
 * [                        ... workspace ...                           ]
 * [objects][tables ->] free space [<- buffers][<- aligned][<- init once]
 *
 * The various objects that live in the workspace are divided into the
 * following categories, and are allocated separately:
 *
 * - Static objects: this is optionally the enclosing ZSTD_CCtx or ZSTD_CDict,
 *   so that literally everything fits in a single buffer. Note: if present,
 *   this must be the first object in the workspace, since ZSTD_customFree{CCtx,
 *   CDict}() rely on a pointer comparison to see whether one or two frees are
 *   required.
 *
 * - Fixed size objects: these are fixed-size, fixed-count objects that are
 *   nonetheless "dynamically" allocated in the workspace so that we can
 *   control how they're initialized separately from the broader ZSTD_CCtx.
 *   Examples:
 *   - Entropy Workspace
 *   - 2 x ZSTD_compressedBlockState_t
 *   - CDict dictionary contents
 *
 * - Tables: these are any of several different datastructures (hash tables,
 *   chain tables, binary trees) that all respect a common format: they are
 *   uint32_t arrays, all of whose values are between 0 and (nextSrc - base).
 *   Their sizes depend on the cparams. These tables are 64-byte aligned.
 *
 * - Init once: these buffers require to be initialized at least once before
 *   use. They should be used when we want to skip memory initialization
 *   while not triggering memory checkers (like Valgrind) when reading from
 *   from this memory without writing to it first.
 *   These buffers should be used carefully as they might contain data
 *   from previous compressions.
 *   Buffers are aligned to 64 bytes.
 *
 * - Aligned: these buffers don't require any initialization before they're
 *   used. The user of the buffer should make sure they write into a buffer
 *   location before reading from it.
 *   Buffers are aligned to 64 bytes.
 *
 * - Buffers: these buffers are used for various purposes that don't require
 *   any alignment or initialization before they're used. This means they can
 *   be moved around at no cost for a new compression.
 *
 * Allocating Memory:
 *
 * The various types of objects must be allocated in order, so they can be
 * correctly packed into the workspace buffer. That order is:
 *
 * 1. Objects
 * 2. Init once / Tables
 * 3. Aligned / Tables
 * 4. Buffers / Tables
 *
 * Attempts to reserve objects of different types out of order will fail.
 */
ZSTD_cwksp;

/*-*************************************
*  Functions
***************************************/

MEM_STATIC size_t ZSTD_cwksp_available_space(ZSTD_cwksp* ws);
MEM_STATIC void*  ZSTD_cwksp_initialAllocStart(ZSTD_cwksp* ws);

MEM_STATIC void ZSTD_cwksp_assert_internal_consistency(ZSTD_cwksp* ws) { … }

/**
 * Align must be a power of 2.
 */
MEM_STATIC size_t ZSTD_cwksp_align(size_t size, size_t const align) { … }

/**
 * Use this to determine how much space in the workspace we will consume to
 * allocate this object. (Normally it should be exactly the size of the object,
 * but under special conditions, like ASAN, where we pad each object, it might
 * be larger.)
 *
 * Since tables aren't currently redzoned, you don't need to call through this
 * to figure out how much space you need for the matchState tables. Everything
 * else is though.
 *
 * Do not use for sizing aligned buffers. Instead, use ZSTD_cwksp_aligned_alloc_size().
 */
MEM_STATIC size_t ZSTD_cwksp_alloc_size(size_t size) { … }

/**
 * Returns an adjusted alloc size that is the nearest larger multiple of 64 bytes.
 * Used to determine the number of bytes required for a given "aligned".
 */
MEM_STATIC size_t ZSTD_cwksp_aligned_alloc_size(size_t size) { … }

/**
 * Returns the amount of additional space the cwksp must allocate
 * for internal purposes (currently only alignment).
 */
MEM_STATIC size_t ZSTD_cwksp_slack_space_required(void) { … }


/**
 * Return the number of additional bytes required to align a pointer to the given number of bytes.
 * alignBytes must be a power of two.
 */
MEM_STATIC size_t ZSTD_cwksp_bytes_to_align_ptr(void* ptr, const size_t alignBytes) { … }

/**
 * Returns the initial value for allocStart which is used to determine the position from
 * which we can allocate from the end of the workspace.
 */
MEM_STATIC void*  ZSTD_cwksp_initialAllocStart(ZSTD_cwksp* ws) { … }

/**
 * Internal function. Do not use directly.
 * Reserves the given number of bytes within the aligned/buffer segment of the wksp,
 * which counts from the end of the wksp (as opposed to the object/table segment).
 *
 * Returns a pointer to the beginning of that space.
 */
MEM_STATIC void*
ZSTD_cwksp_reserve_internal_buffer_space(ZSTD_cwksp* ws, size_t const bytes)
{ … }

/**
 * Moves the cwksp to the next phase, and does any necessary allocations.
 * cwksp initialization must necessarily go through each phase in order.
 * Returns a 0 on success, or zstd error
 */
MEM_STATIC size_t
ZSTD_cwksp_internal_advance_phase(ZSTD_cwksp* ws, ZSTD_cwksp_alloc_phase_e phase)
{ … }

/**
 * Returns whether this object/buffer/etc was allocated in this workspace.
 */
MEM_STATIC int ZSTD_cwksp_owns_buffer(const ZSTD_cwksp* ws, const void* ptr)
{ … }

/**
 * Internal function. Do not use directly.
 */
MEM_STATIC void*
ZSTD_cwksp_reserve_internal(ZSTD_cwksp* ws, size_t bytes, ZSTD_cwksp_alloc_phase_e phase)
{ … }

/**
 * Reserves and returns unaligned memory.
 */
MEM_STATIC BYTE* ZSTD_cwksp_reserve_buffer(ZSTD_cwksp* ws, size_t bytes)
{ … }

/**
 * Reserves and returns memory sized on and aligned on ZSTD_CWKSP_ALIGNMENT_BYTES (64 bytes).
 * This memory has been initialized at least once in the past.
 * This doesn't mean it has been initialized this time, and it might contain data from previous
 * operations.
 * The main usage is for algorithms that might need read access into uninitialized memory.
 * The algorithm must maintain safety under these conditions and must make sure it doesn't
 * leak any of the past data (directly or in side channels).
 */
MEM_STATIC void* ZSTD_cwksp_reserve_aligned_init_once(ZSTD_cwksp* ws, size_t bytes)
{ … }

/**
 * Reserves and returns memory sized on and aligned on ZSTD_CWKSP_ALIGNMENT_BYTES (64 bytes).
 */
MEM_STATIC void* ZSTD_cwksp_reserve_aligned(ZSTD_cwksp* ws, size_t bytes)
{ … }

/**
 * Aligned on 64 bytes. These buffers have the special property that
 * their values remain constrained, allowing us to reuse them without
 * memset()-ing them.
 */
MEM_STATIC void* ZSTD_cwksp_reserve_table(ZSTD_cwksp* ws, size_t bytes)
{ … }

/**
 * Aligned on sizeof(void*).
 * Note : should happen only once, at workspace first initialization
 */
MEM_STATIC void* ZSTD_cwksp_reserve_object(ZSTD_cwksp* ws, size_t bytes)
{ … }

MEM_STATIC void ZSTD_cwksp_mark_tables_dirty(ZSTD_cwksp* ws)
{ … }

MEM_STATIC void ZSTD_cwksp_mark_tables_clean(ZSTD_cwksp* ws) { … }

/**
 * Zero the part of the allocated tables not already marked clean.
 */
MEM_STATIC void ZSTD_cwksp_clean_tables(ZSTD_cwksp* ws) { … }

/**
 * Invalidates table allocations.
 * All other allocations remain valid.
 */
MEM_STATIC void ZSTD_cwksp_clear_tables(ZSTD_cwksp* ws) { … }

/**
 * Invalidates all buffer, aligned, and table allocations.
 * Object allocations remain valid.
 */
MEM_STATIC void ZSTD_cwksp_clear(ZSTD_cwksp* ws) { … }

MEM_STATIC size_t ZSTD_cwksp_sizeof(const ZSTD_cwksp* ws) { … }

MEM_STATIC size_t ZSTD_cwksp_used(const ZSTD_cwksp* ws) { … }

/**
 * The provided workspace takes ownership of the buffer [start, start+size).
 * Any existing values in the workspace are ignored (the previously managed
 * buffer, if present, must be separately freed).
 */
MEM_STATIC void ZSTD_cwksp_init(ZSTD_cwksp* ws, void* start, size_t size, ZSTD_cwksp_static_alloc_e isStatic) { … }

MEM_STATIC size_t ZSTD_cwksp_create(ZSTD_cwksp* ws, size_t size, ZSTD_customMem customMem) { … }

MEM_STATIC void ZSTD_cwksp_free(ZSTD_cwksp* ws, ZSTD_customMem customMem) { … }

/**
 * Moves the management of a workspace from one cwksp to another. The src cwksp
 * is left in an invalid state (src must be re-init()'ed before it's used again).
 */
MEM_STATIC void ZSTD_cwksp_move(ZSTD_cwksp* dst, ZSTD_cwksp* src) { … }

MEM_STATIC int ZSTD_cwksp_reserve_failed(const ZSTD_cwksp* ws) { … }

/*-*************************************
*  Functions Checking Free Space
***************************************/

/* ZSTD_alignmentSpaceWithinBounds() :
 * Returns if the estimated space needed for a wksp is within an acceptable limit of the
 * actual amount of space used.
 */
MEM_STATIC int ZSTD_cwksp_estimated_space_within_bounds(const ZSTD_cwksp *const ws, size_t const estimatedSpace) { … }


MEM_STATIC size_t ZSTD_cwksp_available_space(ZSTD_cwksp* ws) { … }

MEM_STATIC int ZSTD_cwksp_check_available(ZSTD_cwksp* ws, size_t additionalNeededSpace) { … }

MEM_STATIC int ZSTD_cwksp_check_too_large(ZSTD_cwksp* ws, size_t additionalNeededSpace) { … }

MEM_STATIC int ZSTD_cwksp_check_wasteful(ZSTD_cwksp* ws, size_t additionalNeededSpace) { … }

MEM_STATIC void ZSTD_cwksp_bump_oversized_duration(
        ZSTD_cwksp* ws, size_t additionalNeededSpace) { … }

#if defined (__cplusplus)
}
#endif

#endif /* ZSTD_CWKSP_H */