1/*
2 * Copyright (C) 1999-2000 Harri Porten ([email protected])
3 * Copyright (C) 2003-2019 Apple Inc. All rights reserved.
4 *
5 * This library is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU Lesser General Public
7 * License as published by the Free Software Foundation; either
8 * version 2 of the License, or (at your option) any later version.
9 *
10 * This library is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * Lesser General Public License for more details.
14 *
15 * You should have received a copy of the GNU Lesser General Public
16 * License along with this library; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
18 *
19 */
20
21#pragma once
22
23#include "IndexingHeader.h"
24#include "PureNaN.h"
25#include "WriteBarrier.h"
26
27namespace JSC {
28
29// Overview of JSArray
30//
31// Properties of JSArray objects may be stored in one of three locations:
32// * The regular JSObject property map.
33// * A storage vector.
34// * A sparse map of array entries.
35//
36// Properties with non-numeric identifiers, with identifiers that are not representable
37// as an unsigned integer, or where the value is greater than MAX_ARRAY_INDEX
38// (specifically, this is only one property - the value 0xFFFFFFFFU as an unsigned 32-bit
39// integer) are not considered array indices and will be stored in the JSObject property map.
40//
41// All properties with a numeric identifier, representable as an unsigned integer i,
42// where (i <= MAX_ARRAY_INDEX), are an array index and will be stored in either the
43// storage vector or the sparse map. An array index i will be handled in the following
44// fashion:
45//
46// * Where (i < MIN_SPARSE_ARRAY_INDEX) the value will be stored in the storage vector,
47// unless the array is in SparseMode in which case all properties go into the map.
48// * Where (MIN_SPARSE_ARRAY_INDEX <= i <= MAX_STORAGE_VECTOR_INDEX) the value will either
49// be stored in the storage vector or in the sparse array, depending on the density of
50// data that would be stored in the vector (a vector being used where at least
51// (1 / minDensityMultiplier) of the entries would be populated).
52// * Where (MAX_STORAGE_VECTOR_INDEX < i <= MAX_ARRAY_INDEX) the value will always be stored
53// in the sparse array.
54
55// Define the maximum storage vector length to be 2^32 / sizeof(JSValue) / 2 to ensure that
56// there is no risk of overflow.
57#define MAX_STORAGE_VECTOR_LENGTH (static_cast<unsigned>(IndexingHeader::maximumLength))
58
59// These values have to be macros to be used in max() and min() without introducing
60// a PIC branch in Mach-O binaries, see <rdar://problem/5971391>.
61
62// If you grow an ArrayStorage array by more than this, then the array will go sparse. Note that we
63// could probably make this smaller (it's large because it used to be conflated with
64// MIN_ARRAY_STORAGE_CONSTRUCTION_LENGTH).
65#define MIN_SPARSE_ARRAY_INDEX 100000U
66// If you try to allocate a contiguous array larger than this, then we will allocate an ArrayStorage
67// array instead. We allow for an array that occupies 1GB of VM.
68#define MIN_ARRAY_STORAGE_CONSTRUCTION_LENGTH (1024 * 1024 * 1024 / 8)
69#define MAX_STORAGE_VECTOR_INDEX (MAX_STORAGE_VECTOR_LENGTH - 1)
70// 0xFFFFFFFF is a bit weird -- is not an array index even though it's an integer.
71#define MAX_ARRAY_INDEX 0xFFFFFFFEU
72
73static_assert(MIN_SPARSE_ARRAY_INDEX <= MAX_STORAGE_VECTOR_INDEX, "MIN_SPARSE_ARRAY_INDEX must be less than or equal to MAX_STORAGE_VECTOR_INDEX");
74static_assert(MAX_STORAGE_VECTOR_INDEX <= MAX_ARRAY_INDEX, "MAX_STORAGE_VECTOR_INDEX must be less than or equal to MAX_ARRAY_INDEX");
75
76// The value BASE_XXX_VECTOR_LEN is the maximum number of vector elements we'll allocate
77// for an array that was created with a sepcified length (e.g. a = new Array(123))
78#define BASE_CONTIGUOUS_VECTOR_LEN 3U
79#define BASE_CONTIGUOUS_VECTOR_LEN_EMPTY 5U
80#define BASE_CONTIGUOUS_VECTOR_LEN_MIN 3U
81#define BASE_CONTIGUOUS_VECTOR_LEN_MAX 25U
82#define BASE_ARRAY_STORAGE_VECTOR_LEN 4U
83
84// The upper bound to the size we'll grow a zero length array when the first element
85// is added.
86#define FIRST_ARRAY_STORAGE_VECTOR_GROW 4U
87
88#define MIN_BEYOND_LENGTH_SPARSE_INDEX 1000
89
90// Our policy for when to use a vector and when to use a sparse map.
91// For all array indices under MIN_SPARSE_ARRAY_INDEX, we always use a vector.
92// When indices greater than MIN_SPARSE_ARRAY_INDEX are involved, we use a vector
93// as long as it is 1/8 full. If more sparse than that, we use a map.
94static constexpr unsigned minDensityMultiplier = 8;
95
96inline bool isDenseEnoughForVector(unsigned length, unsigned numValues)
97{
98 return length / minDensityMultiplier <= numValues;
99}
100
101inline bool indexIsSufficientlyBeyondLengthForSparseMap(unsigned i, unsigned length)
102{
103 return i >= MIN_BEYOND_LENGTH_SPARSE_INDEX && i > length;
104}
105
106inline IndexingHeader indexingHeaderForArrayStorage(unsigned length, unsigned vectorLength)
107{
108 IndexingHeader result;
109 result.setPublicLength(length);
110 result.setVectorLength(vectorLength);
111 return result;
112}
113
114inline IndexingHeader baseIndexingHeaderForArrayStorage(unsigned length)
115{
116 return indexingHeaderForArrayStorage(length, BASE_ARRAY_STORAGE_VECTOR_LEN);
117}
118
119#if USE(JSVALUE64)
120JS_EXPORT_PRIVATE void clearArrayMemset(WriteBarrier<Unknown>* base, unsigned count);
121JS_EXPORT_PRIVATE void clearArrayMemset(double* base, unsigned count);
122#endif // USE(JSVALUE64)
123
124ALWAYS_INLINE void clearArray(WriteBarrier<Unknown>* base, unsigned count)
125{
126#if USE(JSVALUE64)
127 const unsigned minCountForMemset = 100;
128 if (count >= minCountForMemset) {
129 clearArrayMemset(base, count);
130 return;
131 }
132#endif
133
134 for (unsigned i = count; i--;)
135 base[i].clear();
136}
137
138ALWAYS_INLINE void clearArray(double* base, unsigned count)
139{
140#if USE(JSVALUE64)
141 const unsigned minCountForMemset = 100;
142 if (count >= minCountForMemset) {
143 clearArrayMemset(base, count);
144 return;
145 }
146#endif
147
148 for (unsigned i = count; i--;)
149 base[i] = PNaN;
150}
151
152} // namespace JSC
153