Line data Source code
1 : // Copyright 2014 the V8 project authors. All rights reserved.
2 : // Use of this source code is governed by a BSD-style license that can be
3 : // found in the LICENSE file.
4 :
5 : #include "src/base/division-by-constant.h"
6 :
7 : #include <stdint.h>
8 :
9 : #include "src/base/logging.h"
10 : #include "src/base/macros.h"
11 :
12 : namespace v8 {
13 : namespace base {
14 :
15 : template <class T>
16 4555 : MagicNumbersForDivision<T> SignedDivisionByConstant(T d) {
17 : STATIC_ASSERT(static_cast<T>(0) < static_cast<T>(-1));
18 : DCHECK(d != static_cast<T>(-1) && d != 0 && d != 1);
19 : const unsigned bits = static_cast<unsigned>(sizeof(T)) * 8;
20 : const T min = (static_cast<T>(1) << (bits - 1));
21 4555 : const bool neg = (min & d) != 0;
22 4555 : const T ad = neg ? (0 - d) : d;
23 4555 : const T t = min + (d >> (bits - 1));
24 4555 : const T anc = t - 1 - t % ad; // Absolute value of nc
25 : unsigned p = bits - 1; // Init. p.
26 4555 : T q1 = min / anc; // Init. q1 = 2**p/|nc|.
27 4555 : T r1 = min - q1 * anc; // Init. r1 = rem(2**p, |nc|).
28 4555 : T q2 = min / ad; // Init. q2 = 2**p/|d|.
29 4555 : T r2 = min - q2 * ad; // Init. r2 = rem(2**p, |d|).
30 : T delta;
31 63325 : do {
32 63325 : p = p + 1;
33 63325 : q1 = 2 * q1; // Update q1 = 2**p/|nc|.
34 63325 : r1 = 2 * r1; // Update r1 = rem(2**p, |nc|).
35 63325 : if (r1 >= anc) { // Must be an unsigned comparison here.
36 14332 : q1 = q1 + 1;
37 14332 : r1 = r1 - anc;
38 : }
39 63325 : q2 = 2 * q2; // Update q2 = 2**p/|d|.
40 63325 : r2 = 2 * r2; // Update r2 = rem(2**p, |d|).
41 63325 : if (r2 >= ad) { // Must be an unsigned comparison here.
42 28545 : q2 = q2 + 1;
43 28545 : r2 = r2 - ad;
44 : }
45 63325 : delta = ad - r2;
46 : } while (q1 < delta || (q1 == delta && r1 == 0));
47 4555 : T mul = q2 + 1;
48 4555 : return MagicNumbersForDivision<T>(neg ? (0 - mul) : mul, p - bits, false);
49 : }
50 :
51 :
52 : template <class T>
53 1512 : MagicNumbersForDivision<T> UnsignedDivisionByConstant(T d,
54 : unsigned leading_zeros) {
55 : STATIC_ASSERT(static_cast<T>(0) < static_cast<T>(-1));
56 : DCHECK_NE(d, 0);
57 : const unsigned bits = static_cast<unsigned>(sizeof(T)) * 8;
58 1512 : const T ones = ~static_cast<T>(0) >> leading_zeros;
59 : const T min = static_cast<T>(1) << (bits - 1);
60 : const T max = ~static_cast<T>(0) >> 1;
61 1512 : const T nc = ones - (ones - d) % d;
62 : bool a = false; // Init. "add" indicator.
63 : unsigned p = bits - 1; // Init. p.
64 1512 : T q1 = min / nc; // Init. q1 = 2**p/nc
65 1512 : T r1 = min - q1 * nc; // Init. r1 = rem(2**p,nc)
66 1512 : T q2 = max / d; // Init. q2 = (2**p - 1)/d.
67 1512 : T r2 = max - q2 * d; // Init. r2 = rem(2**p - 1, d).
68 : T delta;
69 10377 : do {
70 10377 : p = p + 1;
71 10377 : if (r1 >= nc - r1) {
72 1222 : q1 = 2 * q1 + 1;
73 1222 : r1 = 2 * r1 - nc;
74 : } else {
75 9155 : q1 = 2 * q1;
76 9155 : r1 = 2 * r1;
77 : }
78 10377 : if (r2 + 1 >= d - r2) {
79 3446 : if (q2 >= max) a = true;
80 3446 : q2 = 2 * q2 + 1;
81 3446 : r2 = 2 * r2 + 1 - d;
82 : } else {
83 6931 : if (q2 >= min) a = true;
84 6931 : q2 = 2 * q2;
85 6931 : r2 = 2 * r2 + 1;
86 : }
87 10377 : delta = d - 1 - r2;
88 : } while (p < bits * 2 && (q1 < delta || (q1 == delta && r1 == 0)));
89 3024 : return MagicNumbersForDivision<T>(q2 + 1, p - bits, a);
90 : }
91 :
92 :
93 : // -----------------------------------------------------------------------------
94 : // Instantiations.
95 :
96 : template struct EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
97 : MagicNumbersForDivision<uint32_t>;
98 : template struct EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
99 : MagicNumbersForDivision<uint64_t>;
100 :
101 : template EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
102 : MagicNumbersForDivision<uint32_t> SignedDivisionByConstant(uint32_t d);
103 : template EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
104 : MagicNumbersForDivision<uint64_t> SignedDivisionByConstant(uint64_t d);
105 :
106 : template EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
107 : MagicNumbersForDivision<uint32_t> UnsignedDivisionByConstant(
108 : uint32_t d, unsigned leading_zeros);
109 : template EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
110 : MagicNumbersForDivision<uint64_t> UnsignedDivisionByConstant(
111 : uint64_t d, unsigned leading_zeros);
112 :
113 : } // namespace base
114 : } // namespace v8
|