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1 
2 /*
3  * Copyright 2006 The Android Open Source Project
4  *
5  * Use of this source code is governed by a BSD-style license that can be
6  * found in the LICENSE file.
7  */
8 
9 
10 #ifndef SkMath_DEFINED
11 #define SkMath_DEFINED
12 
13 #include "SkTypes.h"
14 
15 // 64bit -> 32bit utilities
16 
17 /**
18  *  Return true iff the 64bit value can exactly be represented in signed 32bits
19  */
sk_64_isS32(int64_t value)20 static inline bool sk_64_isS32(int64_t value) {
21     return (int32_t)value == value;
22 }
23 
24 /**
25  *  Return the 64bit argument as signed 32bits, asserting in debug that the arg
26  *  exactly fits in signed 32bits. In the release build, no checks are preformed
27  *  and the return value if the arg does not fit is undefined.
28  */
sk_64_asS32(int64_t value)29 static inline int32_t sk_64_asS32(int64_t value) {
30     SkASSERT(sk_64_isS32(value));
31     return (int32_t)value;
32 }
33 
34 // Handy util that can be passed two ints, and will automatically promote to
35 // 64bits before the multiply, so the caller doesn't have to remember to cast
36 // e.g. (int64_t)a * b;
sk_64_mul(int64_t a,int64_t b)37 static inline int64_t sk_64_mul(int64_t a, int64_t b) {
38     return a * b;
39 }
40 
41 ///////////////////////////////////////////////////////////////////////////////
42 
43 /**
44  *  Computes numer1 * numer2 / denom in full 64 intermediate precision.
45  *  It is an error for denom to be 0. There is no special handling if
46  *  the result overflows 32bits.
47  */
SkMulDiv(int32_t numer1,int32_t numer2,int32_t denom)48 static inline int32_t SkMulDiv(int32_t numer1, int32_t numer2, int32_t denom) {
49     SkASSERT(denom);
50 
51     int64_t tmp = sk_64_mul(numer1, numer2) / denom;
52     return sk_64_asS32(tmp);
53 }
54 
55 /**
56  *  Return the integer square root of value, with a bias of bitBias
57  */
58 int32_t SkSqrtBits(int32_t value, int bitBias);
59 
60 /** Return the integer square root of n, treated as a SkFixed (16.16)
61  */
62 #define SkSqrt32(n)         SkSqrtBits(n, 15)
63 
64 /**
65  *  Returns (value < 0 ? 0 : value) efficiently (i.e. no compares or branches)
66  */
SkClampPos(int value)67 static inline int SkClampPos(int value) {
68     return value & ~(value >> 31);
69 }
70 
71 /** Given an integer and a positive (max) integer, return the value
72  *  pinned against 0 and max, inclusive.
73  *  @param value    The value we want returned pinned between [0...max]
74  *  @param max      The positive max value
75  *  @return 0 if value < 0, max if value > max, else value
76  */
SkClampMax(int value,int max)77 static inline int SkClampMax(int value, int max) {
78     // ensure that max is positive
79     SkASSERT(max >= 0);
80     if (value < 0) {
81         value = 0;
82     }
83     if (value > max) {
84         value = max;
85     }
86     return value;
87 }
88 
89 /**
90  *  Returns true if value is a power of 2. Does not explicitly check for
91  *  value <= 0.
92  */
SkIsPow2(T value)93 template <typename T> constexpr inline bool SkIsPow2(T value) {
94     return (value & (value - 1)) == 0;
95 }
96 
97 ///////////////////////////////////////////////////////////////////////////////
98 
99 /**
100  *  Return a*b/((1 << shift) - 1), rounding any fractional bits.
101  *  Only valid if a and b are unsigned and <= 32767 and shift is > 0 and <= 8
102  */
SkMul16ShiftRound(U16CPU a,U16CPU b,int shift)103 static inline unsigned SkMul16ShiftRound(U16CPU a, U16CPU b, int shift) {
104     SkASSERT(a <= 32767);
105     SkASSERT(b <= 32767);
106     SkASSERT(shift > 0 && shift <= 8);
107     unsigned prod = a*b + (1 << (shift - 1));
108     return (prod + (prod >> shift)) >> shift;
109 }
110 
111 /**
112  *  Return a*b/255, rounding any fractional bits.
113  *  Only valid if a and b are unsigned and <= 32767.
114  */
SkMulDiv255Round(U16CPU a,U16CPU b)115 static inline U8CPU SkMulDiv255Round(U16CPU a, U16CPU b) {
116     SkASSERT(a <= 32767);
117     SkASSERT(b <= 32767);
118     unsigned prod = a*b + 128;
119     return (prod + (prod >> 8)) >> 8;
120 }
121 
122 /**
123  * Stores numer/denom and numer%denom into div and mod respectively.
124  */
125 template <typename In, typename Out>
SkTDivMod(In numer,In denom,Out * div,Out * mod)126 inline void SkTDivMod(In numer, In denom, Out* div, Out* mod) {
127 #ifdef SK_CPU_ARM32
128     // If we wrote this as in the else branch, GCC won't fuse the two into one
129     // divmod call, but rather a div call followed by a divmod.  Silly!  This
130     // version is just as fast as calling __aeabi_[u]idivmod manually, but with
131     // prettier code.
132     //
133     // This benches as around 2x faster than the code in the else branch.
134     const In d = numer/denom;
135     *div = static_cast<Out>(d);
136     *mod = static_cast<Out>(numer-d*denom);
137 #else
138     // On x86 this will just be a single idiv.
139     *div = static_cast<Out>(numer/denom);
140     *mod = static_cast<Out>(numer%denom);
141 #endif
142 }
143 
144 #endif
145