SkMath.h revision 4b163ed2c22facbe8891616874ae07ba7827d9c9 
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/**
16 *  Computes numer1 * numer2 / denom in full 64 intermediate precision.
17 *  It is an error for denom to be 0. There is no special handling if
18 *  the result overflows 32bits.
19 */
20int32_t SkMulDiv(int32_t numer1, int32_t numer2, int32_t denom);
21
22/**
23 *  Computes (numer1 << shift) / denom in full 64 intermediate precision.
24 *  It is an error for denom to be 0. There is no special handling if
25 *  the result overflows 32bits.
26 */
27int32_t SkDivBits(int32_t numer, int32_t denom, int shift);
28
29/**
30 *  Return the integer square root of value, with a bias of bitBias
31 */
32int32_t SkSqrtBits(int32_t value, int bitBias);
33
34///////////////////////////////////////////////////////////////////////////////
35
36//! Returns the number of leading zero bits (0...32)
37int SkCLZ_portable(uint32_t);
38
39#if defined(__arm__)
40    #define SkCLZ(x)    __builtin_clz(x)
41#endif
42
43#ifndef SkCLZ
44    #define SkCLZ(x)    SkCLZ_portable(x)
45#endif
46
47/**
48 *  Returns (value < 0 ? 0 : value) efficiently (i.e. no compares or branches)
49 */
50static inline int SkClampPos(int value) {
51    return value & ~(value >> 31);
52}
53
54/** Given an integer and a positive (max) integer, return the value
55 *  pinned against 0 and max, inclusive.
56 *  @param value    The value we want returned pinned between [0...max]
57 *  @param max      The positive max value
58 *  @return 0 if value < 0, max if value > max, else value
59 */
60static inline int SkClampMax(int value, int max) {
61    // ensure that max is positive
62    SkASSERT(max >= 0);
63    if (value < 0) {
64        value = 0;
65    }
66    if (value > max) {
67        value = max;
68    }
69    return value;
70}
71
72/**
73 *  Returns the smallest power-of-2 that is >= the specified value. If value
74 *  is already a power of 2, then it is returned unchanged. It is undefined
75 *  if value is <= 0.
76 */
77static inline int SkNextPow2(int value) {
78    SkASSERT(value > 0);
79    return 1 << (32 - SkCLZ(value - 1));
80}
81
82/**
83 *  Returns the log2 of the specified value, were that value to be rounded up
84 *  to the next power of 2. It is undefined to pass 0. Examples:
85 *  SkNextLog2(1) -> 0
86 *  SkNextLog2(2) -> 1
87 *  SkNextLog2(3) -> 2
88 *  SkNextLog2(4) -> 2
89 *  SkNextLog2(5) -> 3
90 */
91static inline int SkNextLog2(uint32_t value) {
92    SkASSERT(value != 0);
93    return 32 - SkCLZ(value - 1);
94}
95
96/**
97 *  Returns true if value is a power of 2. Does not explicitly check for
98 *  value <= 0.
99 */
100static inline bool SkIsPow2(int value) {
101    return (value & (value - 1)) == 0;
102}
103
104///////////////////////////////////////////////////////////////////////////////
105
106/**
107 *  SkMulS16(a, b) multiplies a * b, but requires that a and b are both int16_t.
108 *  With this requirement, we can generate faster instructions on some
109 *  architectures.
110 */
111#ifdef SK_ARM_HAS_EDSP
112    static inline int32_t SkMulS16(S16CPU x, S16CPU y) {
113        SkASSERT((int16_t)x == x);
114        SkASSERT((int16_t)y == y);
115        int32_t product;
116        asm("smulbb %0, %1, %2 \n"
117            : "=r"(product)
118            : "r"(x), "r"(y)
119            );
120        return product;
121    }
122#else
123    #ifdef SK_DEBUG
124        static inline int32_t SkMulS16(S16CPU x, S16CPU y) {
125            SkASSERT((int16_t)x == x);
126            SkASSERT((int16_t)y == y);
127            return x * y;
128        }
129    #else
130        #define SkMulS16(x, y)  ((x) * (y))
131    #endif
132#endif
133
134/**
135 *  Return a*b/((1 << shift) - 1), rounding any fractional bits.
136 *  Only valid if a and b are unsigned and <= 32767 and shift is > 0 and <= 8
137 */
138static inline unsigned SkMul16ShiftRound(unsigned a, unsigned b, int shift) {
139    SkASSERT(a <= 32767);
140    SkASSERT(b <= 32767);
141    SkASSERT(shift > 0 && shift <= 8);
142    unsigned prod = SkMulS16(a, b) + (1 << (shift - 1));
143    return (prod + (prod >> shift)) >> shift;
144}
145
146/**
147 *  Return a*b/255, rounding any fractional bits. Only valid if both
148 *  a and b are 0..255
149 */
150static inline U8CPU SkMulDiv255Round(U8CPU a, U8CPU b) {
151    SkASSERT((uint8_t)a == a);
152    SkASSERT((uint8_t)b == b);
153    unsigned prod = SkMulS16(a, b) + 128;
154    return (prod + (prod >> 8)) >> 8;
155}
156
157#endif
158
159